What is the relationship between sleep deprivation and obesity? More than one-third of American adults are now obese. This epidemic has been worsening over the past several decades. There are a number of contributing factors, including: excessive caloric intake, decreased physical activity, the interaction between genes and environment, and cultural influences. Over this same period of time, Americans have been sleeping less, and some researchers have begun investigating whether sleep deprivation might contribute to obesity.
We sleep as much as one-quarter less than our ancestors did, with average total sleep time decreasing from 9 hours in 1900 to less than 7 hours over the past 10 years. In 2001, researchers found that sleeping less than 6 hours per night and remaining awake past midnight increased the likelihood of obesity. In 2002, a study of 1.1 million people found that increasing body mass index (BMI) occurred when habitual sleep amounts fell below 7 to 8 hours.
A study done in Virginia in 2005 showed that overweight and obese individuals slept less than subjects of normal weight. Another study in Wisconsin in 2004 showed that when sleeping less than 8 hours, the increase in BMI was proportional to the amount of decreased sleep.
Since 1992, 13 studies of more than 45,000 children have supported the inverse relationship between hours of sleep and risk of obesity. As children sleep less, they are more at risk of becoming obese. In an interesting 2005 study, Reilly reported in the British Medical Journal that short sleep duration at age 30 months predicts obesity at age 7 years, suggesting that poor sleep may have a permanent impact on part of the brain called the hypothalamus that regulates both appetite and energy expenditure.
Laboratory studies tend to support the data from all these population studies. As early as 1999, Spiegel examined sleep restriction and the effect on metabolism by sleep restricting subjects to 4 hours per night for one week. This led to impaired glucose tolerance (a marker of insulin resistance and diabetes) and changes in hormones related to weight gain and hypertension. The changes were reversible with normal sleep times.
In 2004, Spiegel examined the effect of sleep restriction on hormones related to hunger and appetite. It was found that sleep restriction reduced the hormone leptin, which suppresses appetite, by 18%. It also increased the hormone ghrelin, which increases appetite, by 28%. For comparison, 3 days of underfeeding by 900 calories per day causes leptin to decrease by 22%. Moreover, subjects showed subjectively increased appetite for calorie-dense foods with high carbohydrate content.
How might disruption of the body’s natural clock, called the circadian rhythm, through sleep deprivation affect metabolic hormones that regulate appetite? This is the cutting edge of the current research, and a question that has yet to be answered.
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