Sleep timing, shift work affect risk for type 2 diabetes

Shift workers and daytime workers may have an increased risk for type 2 diabetes if their work time interferes with sleep preference, according to research in Diabetes Care.

In a cross-sectional study that surveyed female nurses about shift work and sleeping preferences during a 20-year period, researchers found that the risk for developing type 2 diabetes increased for early chronotypes (self-described “early risers”) with an increasing duration of shift work exposure, whereas late chronotypes saw an increased risk for the disease when working daytime shifts.

Celine Vetter, MD, a researcher at Brigham and Women’s Hospital and Harvard Medical School, and colleagues analyzed data from 64,615 women participating in the Nurses’ Health Study from 2005 to 2011. Beginning in 1989, participants completed a questionnaire every few years assessing their night shift work exposure. In 2009, the cohort completed a questionnaire assessing their sleep preference; participants could categorize themselves as “definitely a morning type,” “more a morning than an evening type,” “more an evening than a morning type,” “definitely an evening type,” and “neither.” Researchers grouped responders (mean age, 54 years) into three categories: Early chronotypes (n = 22,089), intermediate (n = 33,825) and late chronotypes (n = 7,029).

Within the cohort, early chronotypes had a slightly decreased risk for type 2 diabetes after adjustment for multiple factors when compared with intermediate chronotypes (OR = 0.87; 95% CI, 0.77-0.98). Late chronotypes had a significantly increased risk for type 2 diabetes in age-adjusted models, but the risk was nonsignificant after multivariable adjustment, according to researchers.

Researchers found a significant interaction between chronotype and shift work exposure.

Women identified as late chronotypes who never worked rotating night shifts showed a significantly increased risk for type 2 diabetes (OR = 1.51; 95% CI, 1.13-2.02). Women who worked less than 10 years of rotating night shifts had reduced risk estimates for developing type 2 diabetes if they were early chronotypes (OR = 0.84; 95% CI, 0.72-0.98); the risk was less for late chronotypes (OR = 0.93; 95% CI, 0.76-1.13).

Among women who performed 10 or more years of shift work, neither early nor late chronotypes had an increased risk for type 2 diabetes compared with intermediate chronotypes.

“We consistently observed in women a significant interaction between chronotype and shift work, suggesting a slightly lower risk of type 2 diabetes among early chronotypes compared with intermediate chronotypes, which appeared to increase with increasing duration of rotating night shift work,” the researchers wrote.

In contrast, the researchers wrote, late chronotypes saw a significant increase in type 2 diabetes risk when their shift schedule did not involve night work; this link was not observed in late chronotypes who worked consistent, nonrotating night shift work.

“Future studies with more detailed information on number of night shifts worked per month in addition to years of night work may be able to further disentangle possible intensity and duration effects,” the researchers wrote. by Regina Schaffer

Disclosure: The researchers report no relevant financial disclosures.

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