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Night-shift work increased type 2 diabetes incidence in black women over time
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Black women who worked night shift over an extended period of time were at elevated risk for type 2 diabetes, with lifestyle factors and BMI only partly explaining the relationship, according to findings published in Diabetologia.
“The fact that the association remained, though attenuated, after adjustment for lifestyle factors and BMI suggests that additional pathways, such as disruption of the circadian system, may be playing a role,” the researchers wrote.
Varsha G. Vimalananda, MD, MPH, of the Center for Health Organization and Implementation Research, Edith Nourse Rogers Memorial Veterans Affairs Medical Center, Bedford, Massachusetts, and colleagues followed 28,041 participants from the ongoing prospective Black Women’s Health Study between 2005 and 2013 to assess shift work in relation to incident type 2 diabetes.
At baseline, the participants answered questions about having worked night shift. The researchers used Cox proportional hazards models to estimate incident diabetes. Age, time period, family history of diabetes, education and socioeconomic status were included in the basic multivariable model; further models controlled for lifestyle and BMI.
Over 8 years, 1,786 incident type 2 diabetes cases occurred. Compared with never having worked the night shift, HR increased along with duration from 1.17 (95% CI, 1.04-1.31) for 1 to 2 years of night shift work, to 1.23 (95% CI, 1.06-1.41) for 3 to 9 years and 1.42 (95% CI, 1.19-1.7) for ≥10 years.
The association remained after multivariable adjustment (P-trend=.02), did not vary based on obesity status and was greater in women aged >50 years.
“Shift work is associated with disrupted circadian rhythms and reduced total duration of sleep,” the researchers wrote. “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.”
Circadian rhythms do not adjust to a shifted sleep-wake cycle even after many years, according to the researchers; further, the metabolic effects over time likely influence and strengthen the described association.
The researchers highlighted the public health implications and need for further investigation, with non-Hispanic black and non-Hispanic white shift workers accounting for 35% and 28%, respectively, of all US workers.
“There is a need for continued research into facilitating circadian adaptation to shift work and consideration of avoiding shift work in favor of other work arrangements when possible,” the researchers wrote.
Disclosure: This work was supported by grants from the National Institute on Minority Health and Health Disparities and the National Cancer Institute. One researcher reports support from the American Heart Association. The material is based on work, or supported in part by, the Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development.
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