In 2005, research showed that less sleep and higher body mass index (BMI) are related, confirming studies from the 1980s that correlated fewer hours of sleep a night with increased incidence of being overweight. How they were related, and whether one caused the other, was uncertain. What was known is that adults who get seven or more hours of a sleep a night tend to have less body fat than those who get less sleep. Also, the more obese a person gets, the more health problems they have, including sleep disorders, diabetes and hypertension.
The theory is that, when a person is deprived of sleep, the body produces too much ghrelin and not enough leptin. These hormones are involved in the hunger response. Leptin tells the body when it has had enough, and ghrelin tells the body it needs to eat. Ghrelin is also responsible for telling the body to stop burning calories and to store them as fat. Being awake takes more energy than sleeping, throwing off metabolism. Some genetic mechanisms underlying weight gain and obesity are also thought to involve these hormones.
The theory of sleep deprivation leading to obesity
More recent research has pinpointed the cause-and-effect nature of the relationship – sleep deprivation (defined as getting less than seven hours of uninterrupted sleep a night) leads to weight gain in the majority of the population because of an almost 20 percent decrease in leptin and nearly 30 percent increase in ghrelin. Also, in addition to leptin and ghrelin imbalances, cortisol is increased in sleep deprivation. This hormone can make a person crave fatty foods and carbohydrates.
As reported in the Chicago Tribune in 2011, even with a proper diet and exercise, researchers have found that less than six hours of sleep a night can lead to obesity. The problems start immediately – healthy young volunteers who were only allowed four hours of a sleep per night for six nights showed signs of prediabetes due to effects on insulin regulation. The studies also tracked weight gain over nine years, finding that chronic sleep-deprivation has more permanent consequences.
Sleep deprivation and weight gain in children
The findings are not just significant for adults. Children who are deprived of sleep are also at risk of being obese. Children getting less than 10.5 hours of sleep per night are 50 percent more likely to be obese by age seven. A study published in Pediatrics in Jan. 2011 found that among 308 children from Kentucky between the ages of four and 10 years, those who slept the least were more than four times more likely to be obese than those who got the most sleep on average. Children are starting to develop type 2 diabetes, a life-long condition that was previously only seen in adults, and one in three children who were born in 2000 is likely to develop the disease.
Get more to weigh less
According to researchers, children up to age 10 should be getting an average of nine to 11 hours of sleep a night (10-12 hours if under age three). Adults should be getting seven to nine hours if they want to minimize sleep deprivation’s ill effects on their health and weight.
The research indicates that getting enough sleep will help prevent unwanted weight gain in conjunction with other healthy habits. The 2005 NHANES I study is available online from the journal SLEEP.