We all know that getting too little sleep can be a bad thing.
Some people even ask, does sleeping longer make you lose weight.
Regardless of why you're interested in it, getting enough sleep isn't all that easy.
In fact, around a third of workers in the United States get 6 hours or less of sleep per night (4).
With how busy society is that issue really isn’t surprising.
In many cases, people might be trying to work multiple jobs or attempting to juggle a busy work and family life.
For others, the causes of poor sleep might be stress or long work days.
But, there are other factors influencing our sleep patterns that aren’t as obvious.
In 2015, a large group of authors looked at (Dashti et al., 2015) other areas that might influence our sleep duration.
In particular, they were interested in BMI, macronutrient intake and variations in a specific part of the genome.
The results of the study were fascinating and show more about what influences our sleep duration.
The Study Itself
This study used a meta-analysis approach and looked at data from 9 different cohorts.
In total, this meant that the study made use of information on 14,906 individuals.
However, the information the authors were able to gather was not the same across all of the cohorts.
This resulted in some variation in the sample sizes used in the analysis.
Nevertheless, the large sample size overall meant that the study itself was still strong.
As part of this study, a range of different types of information was collected.
- Dietary habits (including percentage of fat, protein and carbohydrates consumed)
In relation to genetics, the authors were specifically looking at variations in the CLOCK gene and the regulatory genes near it.
The gene influences the period of circadian rhythms, as well as how long they persist for.
Variations in this gene might suggest that people naturally fall into different sleeping patterns and may potentially vary in the natural duration of their sleep.
The authors conducted a range of statistical analyses on the data, including a meta-analysis of other studies.
The complexity of the study meant that there were a range of different outcomes. I won’t go through all of the results in this discussion, but I’m going to highlight the most interesting ones.
The first was the relationship between BMI and sleep duration.
After controlling for other variables, the authors found a negative association between sleep duration. This meant that as the duration of sleep increased, the average BMI decreased.
This effect occurred for both genders, although it was strongest in males.
This ties back to that question of does sleeping longer make you lose weight.
The outcome suggests that sleeping longer does contribute to weight loss, but that's not the full story. I'll go into the details more further on in this discussion.
In contrast, the authors didn’t find any significant association between sleep duration and intake of macronutrients.
However, when they stratified the sample and considered age groups and genders separately they found some relationships.
For example, in younger adults more sleep was associated with significantly lower levels of macronutrients.
When considering a range of outcomes, the authors found that a higher habitual sleep duration was associated with a lower BMI and desirable dietary habits (although the habits were age- and sex-specific).
The authors found relatively few associations with variations in the CLOCK gene and there was also some regional variation in the outcomes in this area.
As a consequence, the authors suggested that more research is needed to see the links between CLOCK variations and dietary intake, and between CLOCK variations and sleep length.
Limitations of the Study
As is often the case, this study was limited by its observational nature.
That is most evident when you look at the relationship between BMI and sleep duration.
The observational nature of the study made it impossible to tell which of those factors caused the other, or whether they were interrelated within the sample.
Beyond this, the study was limited by sample choice as all participants were of European descent.
So, more research is needed to see whether similar patterns are found across different groups.
Additionally, the authors noted that some of the information gathered was self-reported.
Self-reported data can be subject to bias, especially in cases where some responses are more socially accepted than others.
Finally, this study only considered sleep duration and not sleep quality.
This was a necessary limitation, but a consideration of sleep quality could have yielded different patterns.
Implications of the Study
The relationship between sleep length and BMI is interesting, and complicated.
This is because the relationship can work in both ways.
For example, it is often argued that getting a full night of sleep can help people lose weight or make gaining weight less likely.
That makes sense too.
After all, people who get enough sleep tend to have more energy, which makes them less likely to turn to food as a substitute.
Besides, sleeping longer does mean that you physically have fewer opportunities to eat (after all, you don’t eat when you’re asleep, do you?).
So, what about BMI?
Well, people who are overweight often sleep for a shorter amount of time because of their weight.
One reason for this is sleep apnea, which involves breathing stopping repeatedly while a person sleeps.
A person with sleep apnea will wake up multiple times in a night, although they might not always be aware of it.
This can decrease the quality of sleep and potentially the length of sleep too.
The most common cause of sleep apnea is obesity (5), so this is one reason for the relationship between BMI and sleep length.
There are other possible associations too.
For example, people who are physically fit might tend to keep to a more ‘normal’ sleeping duration to help promote their health.
The study focused on the direction of the relationship between BMI and sleep duration, so it didn’t cover these complexities.
As such, the study doesn’t really answer the question 'does sleeping longer make you lose weight?'.
Nevertheless, there is still a large amount of research supporting the importance of getting a good night’s sleep.
The outcomes of the study also suggested that some groups of people followed better dietary patterns when they got enough sleep.
That also supports the idea that more sleep is desirable for health.
At the End of the Day
This study was interesting because it considered multiple different angles.
However, the clearest result that the authors found was in relation to sleep duration and BMI – an area that has been extensively studied.
The other main finding was that longer sleep duration was associated with better dietary approaches, in some populations.
Overall, the outcomes of the study didn’t provide a lot of additional information.
Nevertheless, the study did suggest some interesting directions for future research.
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Do you have problems with how long you sleep? What causes the issue for you?