NEW YORK (Reuters Health) - Individuals who are overweight or obese report that they get less sleep per week than their normal-weight counterparts, investigators report.

Dr. Robert D. Vorona and colleagues at Eastern Virginia Medical School in Norfolk interviewed 924 participants, ages 18 to 91 years, who completed questionnaires asking about medical problems and sleep habits.

Three factors affected total sleep time: being a night-shift worker, being a male, and being obese, the team reports in the Archives of Internal Medicine.

Total sleep time decreased as body mass index (BMI) -- a measure of weight in relation to height -- increased except in the extremely obese group. The difference averaged 16 minutes per day between those with normal weight and the heavier participants, amounting to nearly two hours per week.

The results were similar when the investigators excluded subjects with specific sleep disorders, such as obstructive sleep apnea and insomnia.

Vorona's group suggests lost sleep may lead to metabolic and hormonal irregularities. For example, sleep restriction may reduce levels of leptin, a hormone involved in appetite regulation, thus encouraging weight gain.

Or it may simply be related to increased eating during increased time awake, they add.

Although Vorona's group cautions that their study does not establish a cause-and-effect relationship between restricted sleep and obesity, they do "suggest that an extra 20 minutes of sleep per night seems to be associated with a lower BMI."

Obesity is a component of the so-called metabolic syndrome, a cluster of disorders that also include high blood pressure and high blood sugar levels, which increases the likelihood of developing heart disease and diabetes. In a second study in the journal, a Dutch team suggests that the metabolic syndrome has its roots in the transition from adolescence to adulthood.

Dr. Coen D. A. Stehouwer and colleagues at VU University Medical Center in Amsterdam report the results of a study that started in 1977 among 13-year-olds, with a 24-year follow-up period.

By age 36, 10 percent of the participants had developed the metabolic syndrome. Over time, these subjects had shown more marked increases in total body fat, as well as pronounced decreases in fitness levels.

"These associations were independent of each other and, therefore, represent separate potential targets for the prevention of the metabolic syndrome," Stehouwer's group writes.

"It is now critical to determine the importance of a lack of sufficient sleep during the early formative years in putting our youth on a trajectory toward obesity and the metabolic syndrome -- a trajectory that could be altered if sleep loss is indeed playing a role in this epidemic," write Drs. Joseph Bass and Fred W. Turek in a related editorial. The two commentators are based at Northwestern University in Evanston, Illinois.