The increased risk of diabetes seen in shift workers was more pronounced in younger women than older women."Working night shifts for 10 or more years relative to never working the night shift was associated with a 39 percent higher risk of diabetes among women aged less than 50 years compared with 17 percent higher risk in women aged 50 years or over," said Varsha Vimalananda from the Centre for Health Organisation and Implementation Research (CHOIR) at Edith Nourse Rogers Memorial Veterans Affairs Medical Center, Bedford, Maryland.

Shift work is associated with disrupted circadian rhythms and reduced total duration of sleep. Similar to the effects of jet lag, which are short term, shift workers experience fatigue, sleepiness during scheduled awake periods and poor sleep during scheduled sleep periods.

These alterations in the normal sleep-wake cycle have profound effects on metabolism."Even after many years of night-shift work, circadian rhythms do not fully adjust to the shifted sleep-wake cycle. The metabolic effects of long-term shift work likely underlie a part of the association with diabetes that we and others describe and that strengthens with years of exposure to sleep disruption," Vimalananda pointed out.

In the Black Women's Health Study, 28,041 participants free of diabetes provided information in 2005 about having worked the night shift. The women were followed for incident diabetes during the next eight years.

Thirty-seven percent of the women reported having worked the night shift, with five percent having worked that shift for at least 10 years. During the eight years of follow-up, there were 1,786 incidents of diabetes. The study was published in Diabetologia, the journal of the European Association for the Study of Diabetes.

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