Recent studies have linked inadequate amounts of sleep to weight gain, obesity, and an increased risk of developing diabetes. In the past, I have not been impressed with reports that found such an association between inadequate sleep and weight gain — but it's hard for me to ignore the similar findings in several recent studies.

A 2005 report, for example, involving about 25,000 men and women enrolled in the National Health and Nutrition Examination Surveys (NHANES) found higher body mass indexes (BMIs) and more obesity in those subjects who averaged less than 7 hours sleep a night. And a 2007 analysis of NHANES data found a nearly 50-percent increase in the risk of diabetes among those participants averaging less than 5 hours of sleep daily. About 1 in 10 of the men and women surveyed slept less than 6 hours a day, while a comparable number slept for more than nine hours a day.

Both of these studies found that sleeping for 9 hours or more did not lead to weight gain or to a greater incidence of obesity.

Finally, results of a huge door-to-door survey of 87,000 American adults conducted by the National Center for Health Statistics (NCHS, part of the Centers for Disease Control and Prevention), revealed that obesity was greater in those people who slept either less than or more than 7 or 8 hours a day. Obesity rates were 33 percent among those who slept less than 6 hours a night; 26 percent in those getting 9 hours; and 22 percent in those getting 7 to 8 hours of sleep.

The NCHS survey also found that cigarette smoking was more common among those sleeping less than 6 hours (31 percent of this group smoked) or more than 9 hours (26 percent), compared with 18 percent of those who slept 7 to 8 hours. A summary of the results of this study is available from the NCHS.

And other evidence from experimental studies showed that sleep deprivation raised blood levels of hunger-producing hormones and considerably increased appetite. The sleep-deprived subjects especially craved sweets, starches, and salty snacks.

So it begins to look like, besides recommending fewer calories and more exercise to keep off the extra pounds, we should probably also start prescribing more hours of sleep. (In my own case, I have also learned that earlier bedtimes allow me to cut way back on my midnight snacking.)