Shift workers may be prone to diabetes

LESTER HOLT, anchor: We're back with some disturbing health news for anyone working the night shift . Beyond the inconvenience and the disruption there's new evidence showing how the graveyard shift can actually make you sick. We get the story tonight from NBC 's chief science correspondent Robert Bazell .

ROBERT BAZELL reporting: Just when most Americans are getting their normal sleep, 21 million others like nurse Paula Ashy are working nights.

Ms. PAULA ASHY: I average maybe four hours a day. And even on my nights off I average maybe three and a half, four hours sleep. So I'm always tired.

BAZELL: Ashy works at Brigham and Women's Hospital in Boston where new research provides further evidence of how harmful shift work can be. Scientists put 21 healthy volunteers in the sleep lab for three weeks. By changing lights irregularly and taking away clocks and other clues about time they altered the subject's normal body clocks. Within just a few days when the volunteers ate their bodies responded differently to the food with dangerous effects.

Dr. ORFEU BUXTON (Study Author): Glucose levels went much higher and stayed that way for several hours. This was because of decreased insulin release from the pancreas and together these reflect an increased risk of diabetes.

BAZELL: Several studies have shown that shift workers are at higher risk for type 2 diabetes, heart disease and other problems. But this study is one of the first to show exactly how the body is harmed. The diabetes risk was so great that three of the healthy subjects from the study became pre-diabetic during the experiment. Nine days after returning to a regular sleep-wake cycle their metabolism became normal again. The researchers advise that when possible shift workers try to eat when their body clocks are not out of whack. For Paula Ashy and her co-workers know how difficult that can be.

Unidentified Man: It's busy so we don't go on a regular meal breaks.

Unidentified Woman #1: When you're at work you just kind of snack when you get a free minute.

Unidentified Woman #2: You tend to eat more junk.

BAZELL: The shift workers say there is seldom a time when they feel their body clocks are normal because mostly they feel exhausted. Robert Bazell , NBC News, New York.