>> Saturday, October 30, 2010
I'm sure that everyone reading this blog will be familiar with the phenomenon of sleep deprivation - it is something that all of us have experienced, and for some of us, it plagues our daily lives. It turns out that the effect of sleep deprivation goes much farther than just feeling tired; it can actually have a profound effect on body weight and the risk of obesity.
Dr Jean-Phillipe Chaput, a Canadian colleague of mine who also spent time researching at the Department of Nutrition at the University of Copenhagen, Denmark, is an expert in the area of sleep research. For the scientists among you, he provides an excellent video presentation (the website is from Denmark, but Dr. Chaput's presentation is in English - just press play to watch the video. References to the data below can also be located in Dr Chaput's presentation.)
Along with the epidemic of obesity, we have seen a decrease in the overall amount of sleep we get. According to the National Sleep Foundation, the proportion of young adults getting less than 7 hours of sleep per night was 16% in the year 1960; in 2001, this number increased to 37%.
A study from Quebec showed that children with short sleep were more than 3 times more likely to be overweight, and this association was stronger than other risk factors examined such as parental obesity, television viewing time, and physical activity. Amongst adults age 18-65, the same association was found, with short sleepers (5-6 hours) being 3.8 times more likely to be obese than adults sleeping 7-8 hours per night. Again, this risk factor was stronger than the association of obesity with high fat intake in the diet or physical inactivity. It should also be noted that too much sleep is also associated with obesity; the sleep duration with the lowest body mass index in adults is at 7.7 hours per night.
One obvious factor responsible for this association is that we are simply awake for more hours where we may be inclined to eat. More hours awake equates with a longer period of time per day where we are exposed to our toxic environment that pushes food at us everywhere we look. We may also be more inclined to eat during these extra waking hours due to the activities we undertake during those late night hours - often sedentary activities such as computer time or TV, which often results in snacking on unhealthy foods.
However, the story is much more complex than simply being awake for more hours in a day.
There are several hormonal variations with decreased sleep: we see lower leptin levels (a hormone that normally tells us we feel full and also works to stimulate energy expenditure). We also see higher levels of the hunger hormone, ghrelin, in shorter sleepers, thereby increasing the sense of hunger and desire to eat. Some studies also suggest that the stress hormone, cortisol, increases with shorter sleep duration.
There is also evidence to suggest that decreased sleep may decrease basal metabolism; for example, it has been found that there is a decrease in core body temperature with acute sleep deprivation (lower body temperature being associated with a lower basal calorie burn). We also see a decrease in fidgeting and other behaviours such as our body posture when we are sleep deprived, resulting in a lower calorie burn. Think of how you sit when you are well rested - perhaps sitting in a straight backed chair while you work - versus when you are exhausted, you may be more inclined to assume a more relaxed pose on the couch. These differences may be small, but they matter! Also on the energy expenditure side of the equation, we are less likely to engage in active physical activity when we are tired.
For individuals who struggle with their weight, and also for prevention of weight gain, it is important to include a good night's sleep as part of the overall management approach. The optimum amount of sleep appears to be between 7-8 hours for an adult - be sure to set this as a lifestyle priority!
Dr Sue Pedersen www.drsue.ca © 2010 firstname.lastname@example.org
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