A shorter sleep duration is associated with an increased risk of obesity, type 2 diabetes and cardiovascular disease. The data shows that this association is particularly strong between disrupted sleep and obesity. The reasons for this association are not clear but one theory suggests that stress is the common factor. Stress is a known risk factor for Western lifestyle diseases because it increases the risk of overeating, particularly low quality carbohydrate foods. Such foods are often regarded as comfort foods, and evidence suggests that the biochemical response they cause with regard to increases in serotonin production, may be useful as a short-term protective mechanisms against stress. Stress if chronic in nature can also disrupt hormonal balance by depleting the body of adrenaline and other catecholamines. Studies in metabolic wards have shown that sleep deprivation causes overeating and results in a switch to more carbohydrate based sugary foods.
A recent study investigated the association between habitual sleep duration with measures of energy balance in order to determine if sleep deprivation increases the risk of overeating1. To these ends, the researchers asked subjects to record their mean sleep duration per day over the past year. The researchers defined a short sleep duration to be less than 6 hours of sleep per day. The energy total energy intake of the subjects was then objectively measured using radiolabelled water, and this was used to estimate the physical activity of the subjects (by subtracting the resting metabolic rate). The results of this study showed that subject who slept for 8 hours were significantly less likely to be obese than subjects who slept for less than 6 hours. However, the association with sleep and obesity was not linear, suggesting that the relationship may be complex. Getting more than 8 hours of sleep for example did not provide greater benefits to body mass indices compared to obtaining 8 hours of sleep.
The results of this study also showed that there was an inverse association between sleep duration and physical activity. Those who slept more had lower levels of physical activity. The authors estimated that those subjects who slept for 8 hours expended 113 kcals less in physical activity per day than those who slept for 6 hours or less. Some of this may have been due to the longer duration of wakefulness experienced by those on less than 6 hours sleep, something that gave them more opportunity to perform physical activity. However, the increased physical activity was accompanied by an increase in energy intake that was greater than the amount of energy expended in physical activity. For example, subject obtaining less than 6 hours sleep per day had an energy intake of around 240 kcal greater than those obtaining 8 hours of sleep (but extra physical activity accounted for only 113 kcals per day). If these extra calories were of low quality, they may therefore contribute to obesity.
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