Shift work plus unhealthy lifestyle add up to high diabetes risk
medwireNews: The total diabetes risk associated with the combination of rotating shift work and an unhealthy lifestyle is greater than that of the two added together, shows an analysis of the Nurses’ Health Studies (NHS).
“Our findings suggest that most cases of type 2 diabetes could be prevented by adherence to a healthy lifestyle, and the benefits would be larger in rotating night shift workers,” the researchers write in The BMJ.
However, Zhilei Shan (Harvard TH Chan School of Public Health, Boston, Massachusetts, USA) and team caution that their findings from female nurses, who were almost all White, do not necessarily apply to men and other racial groups.
There were 55,324 participants in the original NHS and 88,086 in the follow-up study. The nurses provided data in 1988 and 1991, respectively, about their working patterns, and a respective 5474 and 5441 nurses developed type 2 diabetes during follow-up.
Having an unhealthy lifestyle had the largest effect on diabetes risk; women with at least three unhealthy lifestyle factors (eg, overweight, smoking, low physical activity) had a more than fivefold increased risk relative to those with none.
But the rate of diabetes also rose with longer duration of shift-working. In the original NHS cohort rates per 100,000 person–years were 440 among those who had never worked shifts compared with 679 among those who had done so for 10 years or more. The corresponding rates per 100,000 person–years in the follow-up study were 251 and 509.
In the two cohorts combined this equated to a significant 16% increased risk for diabetes in nurses with at least 10 years of shift-working relative to those with none, after accounting for factors including age, family history of diabetes, lifestyle, and BMI. The combination of shift-working with an unhealthy lifestyle raised diabetes risk more than sevenfold.
The increased risk associated with these two factors in combination was 71.2% accounted for by unhealthy lifestyle, and 17.1% accounted for by shift work. But the final 11.3% was accounted for by an additive effect of the two.
Shan and team note, however, that this statistical additive interaction may not equate to a causal effect.
And they stress: “From a public health standpoint, because 71% of the joint effect could be attributed to an unhealthy lifestyle, our findings underscore the importance of maintaining a healthy lifestyle.”
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