The study, involving more than 175,000 nurses, found that those who worked night shifts three or more times a month were more likely to develop type 2 diabetes over 20 years compared with people who didn’t work night shifts. Those who worked night shifts for one to two years had nearly no increased risk, while those who did them for three to nine years had a 20 percent greater risk of diabetes, with risks continuing to rise with more years of night shift work. Those who worked nights for more than 20 years had a nearly 60 percent greater risk of diabetes, according to the research published in the journal PLoS Medicine .

Night shift work has long been associated with a string of health problems such as sleep disorders and an increased risk of obesity, diabetes, and heart disease. In a new study, Harvard School of Public Health researchers quantified just how much rotating shift work contributes to the risk of diabetes -- which occurs in 1 in 12 American adults -- and it’s pretty significant.


While the new study doesn’t prove that night shift work actually causes diabetes, other research has shown that those who come off a night shift tend to have higher insulin levels and higher levels of inflammation -- both involved in diabetes -- possibly due to a disruption in the body’s delicate circadian rhythms. These internal body clocks time the release of various hormones to rev us up in the morning and help us wind down at night.

Night shift workers also had higher obesity rates, which is an independent risk factor for diabetes. “We found these body weight differences explained 50 percent of variation, while night shift work explained the rest,” said study leader An Pan, a research fellow at the Harvard School of Public Health.


But it’s hard to tease one from the other since night shift work, itself, could contribute to obesity by causing sleep deprivation, which increases appetite and leads to overeating. (About one-third of night shift workers reported sleeping fewer than six hours a night compared with one-quarter of those who never worked nights.)

“I think rotating shift work tends to lead to an unhappy lifestyle,” said Pan, “with more smoking, not a lot of time for physical activity, and inadequate sleep time.”

That said, Pan acknowledges that some people -- doctors, engineers, and air traffic controllers alike -- must take on night shift work at some point during their careers. Here’s what he recommends to minimize risks of night shift work:

1. Make adequate sleep a priority. If you know you have to work a night shift during the week, make sure to get 9 or 10 hours of sleep on the two previous nights. Stocking up on extra sleep can minimize the effects of sleep deprivation.

If you work the graveyard shift every night, make a plan to sleep seven to eight hours in a quiet darkened room when you get home in the morning. That may mean calling on family members for support with scheduled errands or carpools.

2. Commit yourself to daily exercise. That will help you maintain a healthy weight over time and will help you sleep better during nights you don’t have shift work.

3. Minimize caffeine. Drinking energy drinks or caffeinated coffee to get you through the night shift can take its toll by interfering with your sleep after work. Try to avoid all caffeine within eight hours of your scheduled bedtime.


Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.