Risk for type 2 diabetes appears to be approximately 30% higher among people working more than 55 hours per week doing manual labor or other low socioeconomic status jobs, new data published in The Lancet Diabetes & Endocrinology suggest.

Mika Kivimäki, PhD, and colleagues conducted a systematic review and meta-analysis of four published studies and 19 studies with unpublished individual-level data on 222,120 men and women from the United States, Europe, Japan and Australia that looked at the effects of working long hours on type 2 diabetes.

Long working hours were defined as working 55 hours or more per week while standard working hours were defined as 30 to 40 hours per week.

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Study Findings

A total of 4,963 people developed diabetes during 1.7 million person-years at risk, with an incidence of 29 per 10,000 person-years, according to the study results. The researchers reported a minimally adjusted summary risk ratio of 1.07 (95% CI, 0.89-1.27), equating to a difference in incidence of three cases per 10,000 person-years, for long vs. standard working hours. Heterogeneity in study-specific estimates was significant.

When evaluated according to socioeconomic status, results revealed a significant association between working long hours at a low socioeconomic status job and diabetes (risk ratio=1.29; 95% CI, 1.06-1.57), equating to a difference in incidence of 13 per 10,000 person-years. This association, however, was not found in the high socioeconomic status group (risk ratio=1.00; 95% CI, 0.80-1.25; equating to a difference in incidence of zero per 10,000 person-years).

The researchers noted that the association held strong even after accounting for health behaviors, such as smoking and physical activity, and other risk factors, including age, sex and obesity. Excluding shift work, which has been shown to increase obesity and type 2 diabetes risk, also did not attenuate the association.