MONDAY, March 2 -- Working the night shift might lead to hormonal and metabolic changes that raise risks for obesity, diabetes and heart disease, researchers say.

"In the long run, the physiological impact of shift work on several markers involved in the regulation of body weight -- leptin, insulin, cortisol -- seems to contribute to the increased risk for the development of diabetes, cardiovascular disease and obesity," said study author Frank Scheer, an instructor of medicine in the division of sleep medicine at Brigham and Women's Hospital and Harvard Medical School, in Boston.

Scheer and his team report the findings in the March 2 online issue of the Proceedings of the National Academy of Sciences.

The authors point out that about 8.6 million Americans perform shift work, which the National Sleep Foundation defines as any type of schedule that falls outside the standard nine-to-five norm for business hours. In the United States, factory workers, hospital staff, policemen, firefighters, pilots, road crews and truck drivers are some of the positions that commonly entail some degree of shift work.

This type of work has been previously associated with gastrointestinal problems, fatigue and poor sleep, the researchers noted. Such complications are thought to arise from a chronic disconnect between the waking and eating habits the work demands and the body's innate 24-hour sleep/wake clock, commonly known as the circadian rhythm.

To explore how such a misalignment might raise the risk for developing serious health issues, Scheer and his colleagues conducted a laboratory test designed to mimic the acute effects of jet lag and/or the chronic impact of regular shift work.

In the experiment, the bodily responses of five men and five women were tracked as they stuck to an ever-changing sleep/eat schedule for 10 days.

By the study's conclusion, all the volunteers had eaten and slept across all phases of the circadian cycle, as they followed a daily schedule artificially fashioned along 28-hour blocks.

The results: circadian misalignment provoked a drop in levels of the weight-regulating hormone leptin. Plummeting leptin levels could hasten the onset of obesity and heart disease by prompting increases in appetite and decreases in activity, the researchers said.