Eat, move, ... but sleep too!

18 January 2012

The time spent asleep tends to decline in modern societies. However, lack of sleep is strongly suspected to promote obesity and a number of diseases of civilization.

16% of young adults living in the United States slept less than 7 hours a day in 1960, rising to 37% in 2001. The shortening of sleep time is a general phenomenon observed for some time in a number of countries known for their "productivity", even where we note an increase in the rate of obesity and overweight. Some studies show that sleeping less than 7 hours a day may increase the body mass index (BMI) and waist circumference.

A study of families in Quebec (Quebec Family Study) shows that the most important explanatory factors of obesity are not those that directly influence energy expenditure or calorie intake. Inadequate intake of calcium, disinhibited behavior in relation to food and even more lack of sleep are predictors of obesity above all others, a much larger factor than parental obesity, excessive TV, lack of physical activity or low socio-economic status ...

Deprivation of sleep for a full night reduces energy expenditure and disrupts hormonal cycles. Other studies have estimated that insufficient sleep time could increase the calorie intake for the next day up to 550 kcal. In a regime to lose weight, it was also observed that those who slept only 5.5 hours per night ate more and lost less body fat than those who slept 8.5 hours. Thus, sleep deprivation may affect the hormones that regulate appetite. With lower leptin levels, increased ghrelin levels and cortisol, there is an increased desire to eat and a decreased glucose tolerance. Hypoglycemia related to changes in sleep time increases glucose intolerance. Hence a greater risk of developing type 2 diabetes. Sleeping less than 6 hours a night, multiplies by 2.4 the risk of overeating compared to 7-8 hours a night.

The threshold seems to be around 6 hours of sleep, with exceptions. The short sleepers in perfect health are rewarded with longevity.