A Complete Updated Look at Vitamin D Benefits

Taking a pill

Our society is becoming obsessed with the idea of supplements and people often take these blindly without knowing or considering what effect the nutrient or vitamin is going to have on them.

Some supplements really are important to take, but it’s important to understand why and what impact specific supplements are going to have. Perhaps the most important supplement out there is vitamin D.

Vitamin D benefits for health are highly significant and this is something that everyone should at least investigate. This vitamin has become so important because of the way that people live their lives and the patterns of society overall.

It is also an essential micronutrient for ensuring good health through a person’s life (1). As a society, we are spending increasing amounts of time indoors and in front of our computer screens, televisions and devices.

This is an issue because the chemical reaction that creates vitamin D only occurs in the sunlight.

So, as we are spending more and more time indoors, our vitamin D levels are suffering, creating what many are calling a silent epidemic (2).

Yet, the symptoms of low vitamin D are so hard to pick out that most people don’t even realize that they are deficient and certainly don’t do anything about the problem. Getting enough vitamin D is a very real issue and it continues to be overlooked by many people.

Additionally, vitamin D itself can have significant implications for health, especially if you don’t get enough of it.

Vitamin D Benefits and Health

There are a number of different areas where vitamin D has the potential to either improve health or reduce the risk of health issues. This section covers some of the key areas, of vitamin D benefits roughly organized based on the amount of evidence supporting each health claim.

Some of these have been very well studied and have been the subject of a large body of research.

Others have only been the focus of a handful of studies, making it more difficult to determine what relationship is present.

The large amount of potential benefits from vitamin D is partly connected to the fact that vitamin D regulates upwards of 1,000 human genes (3). This may also be a key reason why vitamin D deficiency is associated with so many issues.

Before we go any further, I also want to mention that vitamin D is technically a hormone​ because of the fact that it is something we produce in our bodies. This may be part of the reason that vitamin D has such widespread impacts on health and function.

The Immune System

Woman with a cold

One of the key areas where vitamin D benefits may be significant for health is in the immune system.

The immune system plays a critical role in the body, helping to protect it from a wide range of infections and diseases.

In fact, differences in the strength of the immune system are often the reason why some people get sick much more often than other people.

Some researchers argue that vitamin D supplementation may be particularly important in the winter months where people may not get sufficient vitamin D from the sunlight and are also less likely to be outside.

This may result in decreases in the strength of the immune system and may predispose individuals to some health issues, such as respiratory infections (4).

This may be part of the reason why people tend to get sick more often in the winter months and why winter is commonly associated with colds, flu and illness in general.

A growing body of research is beginning to link vitamin D to the immune system with many indications that vitamin D deficiency may result in a compromised immune system (5). For example, one study indicated that low levels of vitamin D were associated with an increased risk of postoperative infections in patients who had cardiac surgery (6).

The potential immune system role of vitamin D may also extend to vitamin D having direct effects against viruses (7). A randomized double-blind placebo-controlled study looked at supplementation with 1200 IU of vitamin D per day among schoolchildren in the winter months.

The authors of the study found that supplementation with vitamin D was able to reduce how often influenza A occurred, particularly among children who had not been taking vitamin D supplements prior to the study (8).

A meta-analysis of research into vitamin D and respiratory infections found a similar outcome.

Sick in bed

In that meta-analysis, respiratory-tract infection events were less common among the group taking vitamin D supplements than they were among those not taking vitamin D (9).

Likewise, one study found that vitamin D deficiency was high among adults hospitalized with community-acquired pneumonia (10), suggesting that the deficiency may have increased the chance of pneumonia development.

Vitamin D has also been linked to inflammatory bowel disease, with early research suggesting that treatment with vitamin D may alter the immune response to inflammatory bowel disease (11) and help people to remain in remission longer (12). There has also been some evidence that vitamin D may help to fight inflammation in general, which suggests a role in fighting a number of inflammation-based diseases (13).

Likewise, vitamin D has been linked to an improvement in respiratory diseases, including asthma, through its impact on the immune system as a whole (14).

Another example of the role of vitamin D in the immune system is the potential for vitamin D to be used as a treatment for urticaria (otherwise known as hives). Urticaria frequently occurs as an allergic reaction, but there are also many patients who experience the issue as an autoimmune reaction.

Having a vitamin D deficiency may play a key role in the development of the autoimmune version of urticaria. One study found that supplementation with vitamin D was able to help improve the symptoms of uritcaria (15).

Similar outcomes have been found for atopic dermatitis, which is a long-term skin disease also known as eczema.

A study on vitamin D and atopic dermatitis found that vitamin D supplementation resulted in a decrease of symptoms of the disease (16). Likewise, vitamin D deficiency has been linked with the presence and severity of atopic dermatitis in children (17).

One area of research into vitamin D and the immune system is a consideration of the mechanism of this action. Analyses of the genome have provided indications of key molecules involved in the pathway.

Representation of DNA

This research has also suggested that vitamin D may play a key role in both the adaptive and the innate immune responses of the human body (18).

In many cases, vitamin D plays a role in the immune system as a precursor, with latter compounds having a direct role (19).

One way that this occurs is the way that vitamin D can promote the production of a family of compounds called cathelicidins (20).

Cathelicidins play a key role in the immune system and help to protect against bacterial infections (21).

Another role of vitamin D in the immune system is helping to regulate calcium homeostasis, which involves ensuring adequate levels of calcium in the body. This is a particularly important role because calcium plays a key role in a number of different processes in the body (22).

Additionally, vitamin D has been linked to the production of peptides with antimicrobial properties and these are able to directly kill pathogens in the body (23).

Finally, vitamin D has also been linked to changes in the expression of DNA and in DNA repair. Both of these areas have the potential to improve immune system functioning (24).

Vitamin D may help to boost the immune system and may play a role in disease treatment because of this

Life Length

An extensive study into vitamin D benefits and health considered serum levels of vitamin D across a sample of 14,641 males and females living in Norfolk in the United Kingdom. Vitamin D concentrations were initially measured between 1997 and 2000 and participants were then followed up with in 2012.

Elderly woman drinking coffee or cocoa

The study authors broke the participants down into five key categories based on their baseline serum concentrations of 25(OH)D. These categories were:

  • <30 nmol/L (<12 ng/ml)
  • 30 to <50 nmol/L (12 ng/ml to <20 ng/ml)
  • 50 to <70 nmol/L (20 ng/ml to <28 ng/ml)
  • 70 to <90 nmol/L (28 ng/ml to <36 ng/ml)
  • ≥90 nmol/L (≥36 ng/ml)

The authors found that higher concentrations of 25(OH)D (a measure of vitamin D concentration) were associated with a lower overall risk of heart disease and mortality (25).

A similar study considered morality and vitamin D concentrations among a sample of 9,578 participants, 5,469 of whom participated in the follow up.

The authors found that participants that had vitamin D deficiency (<30 nmol/L) or an insufficiency of vitamin D (between 30nmol/L and 50nmol/L) had a higher risk of death than those with sufficient vitamin D.

This included an increased risk of cardiovascular mortality, an increased risk of cancer mortality and an increased risk of morality as the result of respiratory disease (26).

A meta-analysis of 159 randomized trials concerning vitamin D intake and morality found that in almost all relevant studies increased levels of vitamin D was associated with a decreased risk of morality.

The authors also noted that the observed impact was significant for vitamin D3 only, not for vitamin D2 or any active forms of vitamin D (27). Now, I've talked about the forms of vitamin D in a different post but essentially vitamin D2 is a plant-based form of vitamin D and does not appear to be used as effectively or offer the same health benefits as the form vitamin D3 in humans. 

Another study into vitamin D concentration and mortality considered the relative risk of death among 15,099 participants across a 15 year follow up period. This study confirmed the presence of a J-shaped relationship between vitamin D consumption and risk of death that was found in another study.

Vitamin D

Relationship between vitamin D level and morality rate. Data from Sempos et al., 2013

This relationship suggests that vitamin D can significantly decrease morality rate, but at higher concentrations it can potentially have negative impacts (28).

However, it is important to note that this study is observational in nature. This means that it can see a pattern but cannot work out whether there is a cause and effect relationship. For this particular study, the only level associated with a significantly higher level of mortality was 120 nmol/L. This is equivalent to around 48 ng/ml.

The idea that high levels of vitamin D can damage health is one potential explanation for the trend in the graph above. However, another possible explanation is that the people who fall under that category were ill and were using natural remedies as a form of treatment, including vitamin D supplementation.

In reality, there are many possible explanations for the higher mortality associated with this particular dose of vitamin D and most of these are not directly related to the vitamin D level itself.

In many ways, the connection between vitamin D and life length may be connected to the various vitamin D benefits. After all, there are many different factors that can help to extend life, especially in terms of reducing the risk of disease or issues like falls.  ​

Observational research suggests that having adequate vitamin D may lengthen life, although causation has not yet been shown

Reduced Risk of Falls and Fractures

For many elderly, a serious area of risk is falls.

Among this age group falls are the most common cause of both injuries and death, and the event can also lead to a fear of falling, resulting in decreased mobility (29).

Vitamin D has been linked to a decreased risk of falling, in part because of its role in strengthening bones. One study examined this topic in a randomized controlled trial involving 124 residents of a nursing home.

In this study participants received one of four doses of vitamin D (200 IU, 400 IU, 600 IU or 800 ID) or they received a placebo. The outcomes from the study can be seen in the graph below:

Vitamin D and falls

Vitamin D doses and falls in a randomized controlled trial. Data from Broe et al., 2007

Notably, the participants who took 800 IU of vitamin D had a significantly lower percentage of falls compared to the other groups.

While the results for 200, 400 and 600 IU does appear to be higher than the placebo, it’s important to note that this difference isn’t large and wasn’t statistically significant (30).

Another study found that an oral supplement of 100,000 IU vitamin D every four months was able to significantly reduce fractures in elderly living in the community without any negative health impacts (31).

However, the authors did note that a single dose may not be adequate to provide the required vitamin D throughout the year. Ideally, smaller doses of vitamin D on a more regular basis tend to be more effective as this helps keep vitamin D levels in the blood more stable.

One study also indicated that supplementation with vitamin D resulted in modest improvements in markers of quality of life and bone health (32).

A meta-analysis of studies on vitamin D supplementation and fractures found that doses of vitamin D from 700 IU to 800 IU per day significantly reduced the risk of hip and other fractures compared to calcium or a placebo.

However, doses of 400 IU were not associated with any significant benefit (33).

Research has also indicated that higher vitamin D levels may be needed in people who are active and engage in high impact activity. So, people in this category may need more vitamin D to reduce their risk of stress fractures (34).

Interestingly, there is also some evidence that vitamin D may help in repair following an injury, including in the processes of increasing mineral density in bones and strengthening skeletal muscles (35). However, research in this area is relatively limited.

Vitamin D may reduce falls and fractures, partially by strengthening bones

Cardiovascular Disease and Blood Pressure

Older woman having blood pressure measured

Some research suggests that vitamin D may play a key role in protecting against cardiovascular disease and improving heart health overall.

Furthermore, a deficiency of vitamin D may be a risk factor for cardiovascular disease.

A meta-analysis of the topic looked at the outcomes of 19 independent studies that collectively considered 65,994 participants, 6,123 of whom had cardiovascular disease.

The authors found that across the studies, higher levels of 25(OH)D were associated with a lower level of relative risk for coronary heart disease, stroke, death from cardiovascular disease and cardiovascular disease present (36).

The levels of vitamin D considered in this study ranged from 20 to 60 nmol/L (this converts to from 8 ng/ml to 24 nh/ml), suggesting that 60 nmol/L may offer significant health benefits in relation to cardiovascular disease.

The mechanism behind vitamin D and cardiovascular health has not yet been determined, but some ways that vitamin D deficiency may contribute to the risk of cardiovascular disorders include (37):

  • Developing electrolyte imbalances
  • Disrupted immune response
  • Dysfunction of β-cells
  • Activation of the RAS

Another study indicated the presence of a relationship between vitamin D deficiency and the development of hypertension.

While research on the causal nature of this relationship is still being examined it does appear likely that vitamin D deficiency is the cause of the change in hypertension risk, suggesting the benefits of vitamin D supplementation (38).

Likewise, one study found a positive associated between vitamin D deficiency and coronary artery calcification (39).

More research is needed in this area, as current research has confirmed the presence of an association between vitamin D and several different cardiovascular disorders, but the presence of a causal relationship hasn’t yet been proven (40).

Observational research has suggested that vitamin D deficiency may increase the risk of heart disease


Person with diabetes measuring blood sugar levels

Observational studies have indicated an association between low levels of vitamin D, dairy or calcium and the presence of type 2 diabetes or metabolic syndrome.

Trials with supplementation have indicated that supplementation with vitamin D and calcium may be important for improving outcomes and decreasing diabetes risk in high risk populations (41).

Additionally, this supplementation may play a key role in improving glucose metabolism (42).

A birth-cohort study examined the relationship between vitamin D and type 1 diabetes in a population of 12,231 live births. The study found that vitamin D supplementation in infancy was associated with a decreased risk of type 1 diabetes (43).

A meta-analysis of five observational studies on the topic also found similar outcomes, suggesting that supplementation with vitamin D in early childhood can act as a preventative agent for the development of type 1 diabetes (44).

Some research has also indicated that this impact extends to the development of type 1 diabetes in adolescence (45). This particular study was observational like the previous ones discussed, but also had a relatively low sample size (25 adolescents), which limits its reliability.

Additionally, the authors noted that vitamin D repletion (i.e. high levels of vitamin D) for a period of six months did not have any impacts on inflammation or glycemia, which further calls the results of the study into question.

This strongly suggests that more research is needed in this area, particularly through randomized controlled trials.

Vitamin D pills

However, some experimental studies have been conducted and these reinforce the potential vitamin D benefits for people with diabetes.

For example, one study indicated that vitamin D supplementation was beneficial for patients with a diabetic food ulcer, including a positive impact on glycemic control (46).

Another experimental study found that vitamin D supplementation was able to decrease HbA1c levels in diabetic patients (47).

A meta-analysis of randomized trials also looked at this topic. The meta-analysis found no impact of vitamin D on insulin resistance in patients with prediabetes. However, the supplementation did reduce HbA1c levels and fasting blood glucose levels (48).

Supplementation with vitamin D in infancy may decrease the risk of diabetes

Cancer Risk

One of the roles of vitamin D is as a precursor to a steroid hormone called calcitriol. This hormone is associated with a number of roles across the body.

In particular, calcitriol plays a role in the regulation of cell pathways that play a role in the risk and prognosis for cancer. As such, there is significant potential for vitamin D deficiency to increase the risk of cancer development.

Furthermore, this suggests that the use of vitamin D supplements to avoid deficiency may decrease the risk of cancer and improve the outcomes of the disease (49).

Vitamin D itself also has the potential to play a role in cancer prevention and in the outcomes of cancer. Research has indicated that vitamin D can inhibit the growth of some cell lines of prostate cancer (50).

A large cohort study also reported that participants who had 50nmol/L or more vitamin D had a decreased risk of death from cancer (51). Likewise, an observational study found that women who had lower levels of 25(OH)D had a higher risk of breast cancer tumors that had an unfavorable prognosis (52).

However, not all studies have found this conclusion.

One similarly large study found no association between vitamin D levels and decreased cancer morality (53). The varied results suggest that more examination needs to be undertaken concerning the relationship between vitamin D and cancer.

There is some indication that vitamin D may decrease cancer risk, although the research is in its early stages

Oral Health

Woman brushing teeth

It might seem a bit surprising, but higher levels of vitamin D have also been linked to improvements to oral health.

One study on this topic examined the relationship between 25(OH)D levels and dental health for 1,048 children.

After controlling for possible confounding variables, the authors found a significant relationship between a 10 nmol/L increase in 25(OH)D and a lower chance of molar-incisor hypomineralization.

Additionally, the children with higher levels of 25(OH)D had lower levels of affected teeth, suggesting an improved level of dental health overall (54).

A longitudinal study looked at the possible relationship between 25(OH)D levels and three different oral health issues. The issues in question were tooth loss, periodontis and caries (another word for cavities or tooth decay).

The study examined outcomes from 1,904 participants across a five-year period.

When all possible confounding factors were taken into account, the authors found that levels of 25(OH)D were negatively associated with tooth loss. This suggests that vitamin D may as a preventative factor and may help to prevent against tooth loss.

However, the study didn’t find any relationship between the levels of 25(OH)D and the progression of caries (55).

A similar outcome was found among an elderly population.

In this case, a randomized trial found that the use of calcium and vitamin D supplements were able to decrease the level of tooth loss in participants (56).

Vitamin D has been linked to improved oral health and reduced tooth loss, including in one randomized trial

Vitamin D and Fibromyalgia

Fibromyalgia is a chronic disease that can be devastating to people who suffer from it. It is a complex disease, with a large range of different symptoms. It is a disorder that can be particularly difficult to diagnose, because of many of the symptoms are also related to other disorders, such as depression, sleeping disorders and impacts of diet.

Fibromyalgia often presents with high levels of fatigue and significant pain, making it difficult for people to do many normal components of everyday life. For many, fibromyalgia is also accompanied by mild to severe depression, which can further hinder their ability to do things.

Tired man

In recent years, there has been a considerable focus on the potential connection between vitamin D and fibromyalgia, and many people argue that vitamin D has the potential to significantly reduce the pain that people experience.

Research has indicated that in many cases, people are inaccurately diagnosed with fibromyalgia, when in reality they suffer from vitamin D deficiency (57).

One recent study into vitamin D and fibromyalgia made use of the scientific randomized control structure, providing participants with either vitamin D supplements or placebos.

The study found that there was a significant decrease in the amount of pain experienced by the group that took vitamin D supplements compared to the group that did not.

Additionally, the participants who took vitamin D had increased physical function (58).

Another study found that vitamin D deficiency was very common in conditions that resulted in a significant amount of stress, as the pathway of vitamin D production may be influenced by stress.

The author of this study argued that chronic physical or mental stress may act to decrease the level of vitamin D, resulting in negative health impacts, including vitamin D deficiency (59).

A different study found that there was an association between vitamin D deficiency and the presence of depression and anxiety in patients with fibromyalgia (60).

These outcomes suggest that vitamin D supplementation may well play a critical role for people who experience fibromyalgia. Additionally, as vitamin D deficiency is so often misdiagnosed as fibromyalgia, there is a chance that increasing vitamin D levels will play a key role in health and recovery.

Researchers are still looking into the precise relationship between vitamin D and fibromyalgia, especially as it is not clear how these two areas interact with one another (61).

Vitamin D deficiency has many similar symptoms to fibromyalgia and vitamin D may even help with some of the symptoms of fibromyalgia

Mental Health and Brain Functioning


As I mentioned previously, a deficiency in vitamin D is associated with a higher level of depression, particularly in patients with fibromyalgia. Indeed, vitamin D deficiency has been associated with a number of psychiatric disorders (62).

An observational study compared the vitamin D levels in individuals who attempted suicide (n=59), depressed patients who were non-suicidal (n=17) and healthy individuals (n=14).

The authors found that the individuals who committed suicide had lower mean levels of vitamin D in their blood and more than half (58%) were deficient in vitamin D.

The authors suggest that these outcomes show the need to test vitamin D levels in depressed patients with suicidal symptoms and the provision of vitamin D supplements to vitamin D deficient patients (63).

Likewise, an observational study of German adolescents indicated that higher levels of vitamin D were associated with better mental well-being (64). However, a second study indicated that there was a seasonal variation to this pattern (65) and argued that this meant that vitamin D deficiency may be a consequence of poor mental health, rather than a cause.

Research has also found a link between higher levels of circulating vitamin D and self-rated health levels in men (66). This outcome suggests that vitamin D may impact how we perceive our own health, which may in turn have an impact on mood and even mental health.

Some research has found a link between vitamin D3 consumption and brain functioning. This link is thought to be particularly important for older adults, because this is a period of time where brain functioning often declines (67).

A study on maternal vitamin D levels and infant outcomes found that mothers who were deficient in vitamin D gave birth to infants with lower language development scores (68).


Autism can be a challenging disorder and young children with this disorder experience many difficulties in areas of behavior, communication and social skills.

Early research suggests that there may possibly be a relationship between low levels of vitamin D in infants and during pregnancy and the development of autism.

The theory argues that a deficiency in vitamin D may act as an environment trigger for autism for children already predisposed to the condition (69).

In one case, supplementation with vitamin D3 resulted in an improvement in some of the key symptoms associated with autism (70).

Another study found that a sample of 40 individuals with an autism spectrum disorder (ASD) had significantly lower levels of vitamin D than their siblings, their parents and than 40 age- and gender-matched individuals (71).

A similar study among Chinese children found an association between lower levels of vitamin D in the serum and higher severity of autism (72).

There are also other factors that indicate the possibility of a link between vitamin D and autism. One of these is that DNA mutations can increase the risk for autism, while vitamin D decreases the potential for DNA damage and can also play a role in repairing this damage.

Another interesting link is how dark skin acts as a risk factor for autism (73). As people with dark skin also produce less vitamin D from sunlight, this makes it possible that vitamin D deficiency plays a role in autism development (74).

The research in this area is in far too early stages for any conclusions to be drawn.

However, this research does offer an indication that there may be a relationship between vitamin D deficiency and the development of autism.

Vitamin D may play a role in brain functioning and may help with some mental health conditions 

Symptoms of Low Vitamin D


Vitamin D deficiency is a serious health issue and is much more common than most people assume. Often, people can become deficient in vitamin D because they do not get enough sun exposure and don't get enough vitamin D in their diet.

Historically, one of the major issues with vitamin D deficiency is the development of rickets. This disease results in skeletal deformities and soft bones.

However, it isn’t an issue that is seen much in the modern day because milk and other food products have been fortified with vitamin D.

Nevertheless, the disease is still present in some communities, often exacerbated by calcium deficiency (75).

The fact that milk and other products are fortified with vitamin D often leads people to assume that vitamin D deficiency is no longer a significant health issue in modern society.

This isn’t the case and there is growing recognition that vitamin D deficiency may be an unrecognized epidemic (76).

Now, vitamin D deficiency does have symptoms.

However, the catch is that these symptoms are fairly generalize, so most people don't associate them with vitamin D deficiency. In fact, in many cases, people simply attribute the symptoms to the general challenges of life. For example, some of the key symptoms of vitamin D deficiency include overall aches and pains, depression, bone weakness and fatigue.

All of these symptoms are very generic and are associated with a wide range of other health conditions. They are also things that people often take for granted in their lives, or attribute to lack of sleep or other lifestyle choices.

This is one reason why vitamin D deficiency is often misdiagnosed, normally as fibromyalgia (77). Additionally, many people feel no symptoms at all even when they are vitamin D deficient.

Yet, many of the health benefits from vitamin D come for the fact that vitamin D deficiency causes so many health issues. Because the symptoms of vitamin D deficiency are so unclear and unreliable the first thing for anyone to consider is whether they are likely to be deficient in vitamin D.

Some of the key at-risk groups are discussed below, but generally speaking the most important things to consider are how much time you spend outside in the daylight hours and how well you are covered up during that time.

If you don’t have much sun exposure, then you may well be deficient in vitamin D.

Even if you do get a decent amount of sun exposure, it may still be worth taking the time to find out your vitamin D level in case it is not what you expect.

Vitamin D deficiency is very common but has general symptoms and is largely unrecognized

At-Risk Groups

Group of friends in the sun

Anyone may potentially be vitamin D deficient, but there are some groups that are more at risk than others.

The site Inside Tracker goes into these various groups in more detail. 

If you are a member of an at risk group, you need to be paying much greater attention to your vitamin D intake and make sure that you get enough vitamin D.

Additionally, it's also possible that at-risk groups will see more vitamin D benefits, simply because they are more likely to be deficient in vitamin D.​

Dark Skinned People

The pigment melanin plays a key role in the darkness of people’s skin. This pigment also plays a role in the production of vitamin D and reduces the ability of the skin to produce vitamin D from the obtained sunlight (78).

This means that people with darker skin tend to get less vitamin D from the same level of sunlight as people with lighter skin.

People with Specific Conditions

Some health conditions can also affect the ability to synthesize vitamin D.

Inflammatory bowel disease is one example of this, as well as other conditions that cause issues with the absorption of fat. When individuals have a reduced ability to absorb fat they may need to be supplementing with vitamin D (79).

Vitamin D deficiency is related to the amount of vitamin D in the blood serum, rather than the amount of vitamin D that a person takes in.

As such, people who are obese may need higher levels of vitamin D to achieve a desirable level of vitamin D. While obesity doesn’t change the rate of vitamin D production, it does affect the release of vitamin D (80).

This issue is also significant for individuals who have had bariatric surgery (81).

Older Adults

Older adults tend to have decreased levels of vitamin D for a couple of reasons.

First, as people age their ability to synthesize vitamin D decreases.

Senior in the sun

At the same time, older adults tend to spend more time indoors, resulting in less exposure to the sun and lower levels of vitamin D intake.

Because of this, many older adults are likely to be low in vitamin D (82).

Additionally, elderly who live in facilities may be exposed to high levels of fluorescent and artificial lighting which does not help them develop vitamin D. In many cases they may also not be getting a balanced diet.

People with Limited Sun Exposure

If your sun exposure is limited for any reason, this puts you at increased risk for vitamin D deficiency.

One example of this is individuals who are homebound or who spend very little time outside of the home. This includes people who are disabled or have issues that make leaving the home difficult. This also applies to people who work from home, as they may go outside infrequently.

People who work shift work also often have limited sun exposure, particularly if they are working late into the night and sleeping during the day.

Other people with limited exposure to the sun include those who are always fully covered when they are outside, such as women who wear long robes and face coverings because of their religion.

Infants Who Are Breast Fed

Ordinarily breastfeeding is considered the healthiest approach for feeding an infant.

However, human breast milk typically contains less vitamin D than a growing infant needs unless the mother is supplementing with high levels of vitamin D (83,84).

Mothers also have to be careful when exposing children to sunlight, making sure that they wear protective clothing and are kept out of direct sunlight.

As such, the American Academy of Pediatrics recommends supplementing with 400IU of vitamin D daily, in the form of oral vitamin D drops until the child is drinking milk fortified with vitamin D.

This is something that should be prescribed by a pediatrician (85).

Research also suggests that pregnant women may also need more vitamin D to ensure their health than current guidelines recommend (86).

Dark skinned individuals, older adults, people with limited sun exposure and breast fed infants all have an increased risk of vitamin D deficiency

Vitamin D and Other Nutrients

Refreshing Healthy Milk With Calcium And Nutrition

The human body is complex and any vitamin or mineral is going to have a large number of different interactions throughout the body.

This is why there are often interactions between different medications and between medications and some nutrients.


Vitamin D and calcium are strongly related. This is actually one of the reasons that vitamin D offers so many health benefits.

For example, vitamin D has been associated with maintaining calcium in the plasma, influencing bone formation and resorption. This role varies depending on whether the level of calcium is sufficient or insufficient in the body (87).

In fact, research has even shown that serum calcium levels vary in a similar seasonal manner to vitamin D levels (88).

Indeed, vitamin D is essential for the development and maintenance of bones (89).

So if a person is trying to improve their bones by increasing calcium consumption, they also need to look at supplementing with vitamin D.

Vitamin K2

Vitamin D acts to increase the production of ostocalcin and MGP.

Osteocalcin is a protein responsible for moving protein into the bones, while MGP is responsible for removing calcium from the soft tissues (where it isn’t supposed to be) such as the arteries. Both of these proteins need to activated through carboxylation, something that vitamin D doesn’t do.

Instead, vitamin K2 acts to facilitate carboxylation (and may also be important for health).

So, if you have high levels of osteocalcin and MGP because of vitamin D, but don’t have much vitamin K2 in your body, those two proteins aren’t going to have many benefits.

Supplementing with vitamin D without also increasing vitamin K2 can even have negative health impacts, because a smaller concentration of your MGP is active. This could potentially result in an increased level of calcification of the arteries.


As such, you have to pay attention to your intake of vitamin K2, particularly when you are supplementing with vitamin D.

In fact, it’s possible that this issue has confounded some of the studies into the health benefits of vitamin D.

Osteocalcin is also important for another reason and it plays a key role in building bones and making use of calcium effectively.

This role may mean that vitamin D supplements can increase bone strength and may be why vitamin D decreases the risk of fractures and falls.


Although it is often overlooked, magnesium plays an important role in the metabolism and synthesis of vitamin D. Because of this, supplementation with both magnesium and vitamin D can help to decrease resistance to vitamin D, such as in the treatment of some forms of rickets.

The level of magnesium intake has been shown to play a role in vitamin D status.

This suggests that vitamin D may be more effective in conjunction with magnesium, particularly in cases where the individuals have low levels of magnesium (90).

Indeed, a deficit of magnesium may be a driving factor in the prevalence of vitamin D deficiency (91).

Likewise, high levels of magnesium intake are associated with lower risks of vitamin D deficiency or insufficiency (92).

Vitamin D interacts with other nutrients, including calcium, vitamin K12 and magnesium

Vitamin D Supplementation

Vitamin D supplements are not the only way to get vitamin D into your body, but they can be a very important approach.

They can be particularly relevant for people with limited sun exposure or people who need to recover from a serious deficit in vitamin D.


Woman with vitamin D bottle

Working out dosage of vitamin D can be a bit challenging for a couple of reasons.

First, there is no accepted serum level of vitamin D and there are still many debates about what vitamin D levels are desirable for vitamin D benefits.

Second, people vary a whole lot in the amount of vitamin D that they have in their system. For example, some people may be severely deficient in vitamin D, while others may already be getting enough from other sources.

How much vitamin D you have in your body plays a large role in how much you should be taking. Like most types of vitamins, vitamin D is measured in International Units (IU).

However, recommendations about how much vitamin D a person needs for optimum health varies significantly across sources.

The amount of vitamin D3 that people require is a controversial debate, as the scientific evidence is relatively limited.

The Food and Nutrition Board recommends that people under 70 years of age should be taking around 600 IUs of vitamin D3 each day, with this recommended level increasing to 800 IUs for people above 70 (93).

This difference is due to decreases in the effectiveness of the vitamin D reaction as a person ages.

Research has also indicated that 1,000 IU daily may be needed to ensure that the level of vitamin D is adequate and prevent any negative health impacts (94).

Some groups even recommend as much as 5,000 UI of vitamin D each day.

One research study considered the current information surrounding risk and benefits of vitamin D in humans and argued that the recommended level should be 10,000 IU per day, a level that is more than ten times the current recommended levels (95).

The lack of consensus about vitamin D supplements makes it difficult to determine exactly how much vitamin D a person should be getting.

Vitamin D supplements

Realistically, the value of 600 IU to 800IU that the Food and Nutrition Board is promoting simply doesn’t agree with current research, and it is concerning that the government is choosing to promote this value

This suggests the need for an in-depth study and reevaluation of current vitamin D recommendations and as research continues to focus on the topic, this need may become a reality.

In some cases, the level of vitamin D that a person consumes might be higher, depending on what they are using the vitamin D for. Additionally, people who are severely deficient in vitamin D may end up taking more concentrated supplements, as much as 50,000 UI twice a week.

However, while low levels of vitamin D supplementation are relatively safe, taking high amounts of vitamin D should involve prescription and monitoring by a physician to minimize the risk of any potential side effects.

There is a huge amount of individual variation in the way that vitamin D is produced and how the body interacts with that vitamin D, so the ideal dosage for one person might be completely ineffective for another.

The single most effective way to find out how much vitamin D you should be taking is to find out what your serum level of vitamin D is.

Your primary physician should be able to test this for you and may prescribe you the relevant amount of vitamin D. If they do not, you can test this yourself.

The Vitamin D Council site has useful tables that describe the meaning of different test results and how much supplement you should be taking to correct any issues.

Recommended dosages of vitamin D vary but the best starting point is to find out your own levels, ideally through a physician

Types of Supplement

As with any vitamin, it’s important to pay careful attention to the specific supplement you choose.

One key factor to consider is what form of vitamin D the supplement contains. As I mentioned above, vitamin D­3 is the best for health, largely because of how well it is absorbed.

Pills in hand

Most of the time, supplements will be either vitamin D2, D3 or a combination of the two.

In general, you want to be looking for a supplement that is specifically marketed as vitamin D3.

Anything that just says vitamin D is likely to contain some vitamin D2.

Another thing to consider is the form of the vitamin. Vitamin D is a fat soluble vitamin and tends to be available either as pills or as liquid gel pearls.

The gel pearls are the best option for supplementation, because they are more readily absorbed into the body. Many people also find them easier to take, particularly as they have no taste and are easy to swallow.

The liquid pearl gel variant of vitamin D tends to be absorbed well and is easy to take


It is always important to take safety into account when taking any supplement.

In the United States, the supplement industry is largely unregulated and companies are not required to prove safety or health benefits before the supplement reaches the market.

This means that you should be careful about what company you obtain supplements from and their reputation. The upper dosage for vitamin D is also something to consider.

Research has yet to determine exact upper limits of vitamin D consumption. A report by the Institute of Medicine in 2010 increased the upper limit of vitamin D from its previous level of 2,000 IU to 4,000 IU, although there are indications that more than 4,000 IU may not cause any harm (96).

However, some groups suggest that safe levels of consumption of vitamin D may possibly be as high as 10,000 IU daily without significant side effects.

Woman with question marks

This information is referring to daily doses of the supplement, although people sometimes take much higher doses less frequently to combat vitamin D deficiency.

High doses of vitamin D over extended periods of time may cause symptoms including fatigue, dry mouth, loss of appetite and nausea.

It is relatively difficult to consume toxic levels of vitamin D and because of this, very large doses are often used infrequently for treatment (such as 50,000 IU). In fact, one of the few studies to note vitamin D toxicity did so at a level of 194 ng/ml (97).

Care is always important when taking supplements, particularly in high doses, although very high doses of vitamin D are often prescribed

Medical Perspectives

The most effective and reliable way to find out your vitamin D level is to have it tested by your primary care physician. Your physician may also be able to recommend what dose of vitamin D to take and in some cases may even prescribe it.

As research continues to be conducted on vitamin D, the healthcare profession is beginning to accept the role that vitamin D can have on health.

Because of this, more and more healthcare professionals are beginning to test for levels of vitamin D and to prescribe vitamin D supplements.

As a general rule, doses above 4,000 UI should not be taken without consulting a physician, although a physician may prescribe much higher doses for short periods of time to treat specific conditions.

People who have kidney disease, sarcoidosis, lymphoma or hardening of the arteries should consult a physician prior to taking vitamin D supplements, as vitamin D supplements may act to worsen these conditions.

Consult your primary care physician before taking supplements, particularly if you are on medication or have a health condition

Key Questions and Responses

How Do You Test Vitamin D Levels?

Man and doctor

Often a medical professional will test for vitamin D levels as part of a routine health checkup, particularly if you fall into an at-risk group.

You can also request a test from your medical professional to find out what your levels are. How easy this is will really depend on your medical professional, as the importance of vitamin D is not recognized by everyone.

It is also possible to test your vitamin D levels yourself through test kits.

For example, a site known as Vitamin D Council offers test kits at $50 a piece (or four for $180) and there are other places that offer similar tests.

Personally I get my blood testing done through Life Extension and I have always found the service to be very reliable.

This is an expensive alternative and it is still better to work with your primary physician concerning your vitamin D levels. However, if you cannot do this for any reason, a vitamin D test kit may be a good alternative.

The outcome of a vitamin D test kit should give you a good idea of how much vitamin D you should be taking. Additionally, you may only need to do a few tests to work out the amount of vitamin D supplementation that you need.

However, measuring vitamin D levels is currently done through a test of the levels of 25(OH)D in the blood and this test only gives an approximation of vitamin D levels. There is also growing concern that this method of testing may be inaccurate, which indicates that approaches for testing vitamin D may change in the future (98).

Nevertheless, for the moment, vitamin D testing that looks at 25(OH)D levels is the most viable way to determine your vitamin D levels.

Does Increased Vitamin D Intake Increase Vitamin D in the Blood?


Increasing your amount of vitamin D intake does increase serum levels of 25(OH)D (and by extension vitamin D). Interestingly enough, this relationship is not linear (99).

Instead, as the amount of vitamin D consumed increases, the overall impact on the amount of vitamin D in the blood is lower. So, it takes less vitamin D to go from baseline to a serum level of 25 ng/ml than it does to go from 25 ng/ml to 50 ng/ml.

Body mass index also has an impact on serum levels of 25(OH)D (100), with obese individuals responding slower and less significantly to vitamin D supplementation (101).

As discussed earlier, this also means that obese people are likely to have lower vitamin D than non-obese people. This makes it more likely for obese people to be deficient in vitamin D.

What Level of 25(OH)D is Desirable?

Some research suggests that a level of 40 nmol/L to 50 nmol/L (16 to 20 ng/ml) is consistent with the health requirements of the population (102).

However, other research argues that this level is inadequate for overall levels of health and bone health – instead arguing that you should have a level above 50 nmol/L (20 ng/ml) (103).

Some researchers argue that optimal levels of vitamin D may be as high as 100 nmol/L (40 ng/ml) (104). I have touched on other levels of 25(OH)D throughout this article also.

For example, populations near the equator had levels of 25(OH)D that went up to almost 70 ng/ml. In reality, the desired level of 25(OH)D is one of many areas within this field that is still being heavily debated, and as such there is no clear answer.

I personally feel that aiming for around 45 to 50 ng/ml is a good level, as there are many studies associating this with health benefits. This is also the level that I use myself and I feel that it has improved my health significantly.

Many of the low recommendations for 25(OH)D come from people being overly cautious and from an underestimation of the positive benefits of vitamin D. For example, some research focuses on vitamin D as a supplement only for benefitting the bones – completing ignoring the other health benefits of the vitamin.

The following table shows some of the key guidelines for 25(OH)D levels from a number of locations. As you can see, there are quite a range of values out there, and many more that aren’t included in the table.

Vitamin D levels

Vitamin D guidelines. Data from Vitamin D Council

The National Institutes of Health​ also has other a set of recommendations for vitamin D levels. At present, these are:

  • Deficient: <12 ng/mg
  • Insufficient: 12-20 ng/ml
  • ≥20 ng/ml: Sufficient
  • ≥ 50 ng/ml: Potentially dangerously high (particularly above 60 ng/ml)

Is It Possible to Get Too Much Vitamin D from the Sun?

While many people don’t get enough sunlight, there certainly are people in the opposite camp.

Thankfully, there are control mechanisms involved in the production of vitamin D that prevent excess vitamin D from being created – so this isn’t something that you need to be concerned about.

Final Thoughts

From a research perspective, interest in vitamin D continues to grow, as scientists try to understand more about this vitamin’s mechanisms in the body and the many different vitamin D benefits.

While much still needs to be learned about the vitamin, it is clear that there is much potential for health benefits from having sufficient vitamin D and few associated risks.

Indeed, at this point in time the prevalence of vitamin D deficiency is widely recognized.

Yet at the same time, the healthcare industry has been slow to catch onto the potential of this vitamin.

This is just one example of a time where growing knowledge and research has not been turned into improved solutions and health.

The best solution for just about everybody is to take the time and talk to your primary physician about your vitamin D levels. They are able to test this for you and prescribe you vitamin D based on your needs.

Supplementing with vitamin D is also becoming a common approach, particularly for people who feel that they do not get enough sunlight.

There are now many different brands that offer vitamin D, most frequently in liquid softgel form or as tablets. Even if you aren’t big on taking vitamins, vitamin D is one that you should very seriously consider, even if it is just in the winter months when you aren’t outside very much.

Realistically though, most people will find that they need to supplement with vitamin D every day, even in the summer months - and may need a higher dose in the winter. After all, getting outside in the daylight hours is often difficult for those of us who work full-time, and some of the vitamin D levels that researchers suggest probably aren't attainable by small amounts of daily sun exposure. ​

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