Appeared in Orange Coast Voice newspaper March 2008, page 11
Shorter Sleep Adds on Pounds: Sleep More to Trim Down
by Sarah S. Mosko Ph.D.
Wrong. Recent science suggests that foregoing sleep is contributing to America’s obesity epidemic and that two hormones you have probably never heard of might play center stage.
Physicians use something called the Body Mass Index (BMI) to characterize someone’s weight. BMI is based on both height & weight and is calculated by dividing weight in kilograms by height in meters squared (kg/m2). For adults, a BMI of 18.5 – 24.9 is normal, 25 – 29 is overweight, and >30 is obese.
National health surveys have shown that the percentage of adults with a BMI >30 has more than doubled since 1960. Currently, about 1/3 of adults are obese, and obesity is way up in children too.
Body weight is thought to be under the control of a complex set of factors. That genetics conspire with poor eating habits and lack of exercise to cause a weight problem is well established. But, new findings suggest that sleeping habits are important too.
Although sleep need varies from person to person, the consensus among experts is that most adults need 7-9 hours sleep on a regular basis to feel rested and function optimally. Yet, in an age where “workaholism” has become a near virtue, tending to your sleep needs can be seen as weakness or laziness.
The “2005 Sleep in America” poll conducted by the National Sleep Foundation indicates that many of us fall appreciably short of meeting our sleep requirement. Overall, Americans report averaging only 6.9 hours sleep per night (6.8 hours on weekdays and 7.4 hours on weekends). On weekdays for example, 40% of us sleep less than seven hours, and 16% rack up fewer than six hours. Even on weekends, one in ten still averages under six hours. A full quarter of us report getting “a good night’s sleep” at most a few times a month.
Obesity is significantly more common in individuals with shorter sleep times, according to recent science. For example, in a 2004 study based at the University of Wisconsin that sampled over 1,200 adults, people who slept on average 7.7 hours had the lowest BMI, and BMI went up as sleep time went down. In another study just published in the American Journal of Epidemiology, postpartum women who were sleeping less than five hours at six months were much more likely to be still struggling with weight retention at one year.
Just how limited sleep and obesity are linked is not known. Perhaps longer hours of wakefulness simply translate into more opportunity to raid the fridge. Or, maybe energy expenditure is overall reduced because of fatigue and inactivity.
Recent research, however, has uncovered a likely mechanism involving two appetite-modulating hormones calledleptin and ghrelin. Leptin suppresses appetite, and ghrelin stimulates it. Leptin is produced by fat cells, and ghrelin is made in the stomach. These hormones send opposing messages to the brain to maintain the body’s energy balance.
Human studies have shown that when sleep is curtailed, blood concentrations of leptin fall and ghrelin increase, thus stimulating appetite. For example, when healthy men were restricted to four hours of sleep for just two nights, levels of the two hormones shifted as predicted in opposite directions, and hunger increased 24% (especially for salty, sweet and starchy foods), according to a 2004 study from the Univ. Chicago.
It seems short sleep also makes for chubby kids. Nearly 800 grade-schoolers living in both urban and rural areas were followed over time in a National Institutes of Health study published last year. Of the sixth-graders, nearly one in five was overweight, and shorter sleep was associated with increased risk for overweight.
Perhaps most disquieting is the finding that children with shorter sleep in the third grade were more likely to be overweight by the sixth grade, even if they did not yet have a weight problem. For each additional hour of habitual sleep in the third grade, the chance of being overweight in the sixth grade dropped by ~40%. Whether leptin andghrelin are party to this relationship in children has yet to be studied.
Much remains to be learned about the connection between shorter sleep and BMI in both children and adults. For example, is sleep curtailed voluntarily or as a consequence of something else like sleep apnea, a breathing disorder common in overweight individuals wherein repeated collapse of the airway during sleep causes arousals? In any case, there is already abundant evidence that sleep debt wrecks havoc on other aspects of well-being by undermining mood, cognitive abilities, driving safety, work productivity, and personal relationships. Shorter sleep is even correlated with cardiovascular disease and earlier death.
So, while scientists sort exactly how abbreviated sleep translates into higher BMI, there are solid reasons aplenty to rethink that impulse to burn the midnight oil. If you do not, Mother Nature will likely exact a toll of some sort, perhaps by adding unwanted pounds and inches.