Shift Work Ups Type 2 Diabetes Risk Among Black Women

Miriam E Tucker

January 12, 2015

Working the night shift raises the risk of developing type 2 diabetes among African American women, a new study finds.

"Our findings from the Black Women's Health Study contribute to the observational literature that consistently demonstrates a relationship between disruption of circadian rhythms and long-lasting adverse effects on metabolism, such as obesity and type 2 diabetes mellitus," lead author Dr Varsha G Vimalananda (Boston University School of Medicine, Massachusetts) told Medscape Medical News.

She advised, "Clinicians should discuss the adverse metabolic consequences of shift work and sleep disruption and sleep loss in general with patients, [who] may have some choices in their work schedules and may be able to make behavioral modifications at home that promote sufficient sleep at night."

The results, from an ongoing prospective cohort study of more than 28,000 black women, were published online January 11, 2015 in Diabetologia by Dr Vimalananda and colleagues.

The Longer the Shift Work, the Greater the Diabetes Risk

Beginning in 1995, the Black Women's Health Study examined the determinants of health and disease in 59,000 women aged 21 to 69 years at baseline.

Data are collected every 2 years via questionnaires; information on night-shift work was added starting from 2005. The current study analyzed results from 28,041 women who answered those questions and did not already have diabetes or other serious illnesses at baseline.

Of the total 28,041 women, 21% had worked night-shift jobs for 1 to 2 years, 11% had done so for 3 to 9 years, and 5% for 10 or more years. Between 2005 and 2013, a total of 1786 who were over 30 years of age reported a new diagnosis of diabetes.

After adjustment for age, questionnaire cycle, family history of diabetes, education, and neighborhood socioeconomic status — but not lifestyle factors (exercise, coffee/soda/alcohol consumption, smoking, etc) or body mass index (BMI) — the diabetes incidence increased with night-shift duration, with a hazard ratio of 1.42 for those who had worked the night shift for 10 or more years compared with those who never worked the night shift (P for trend < .0001).

The relationship was attenuated but remained significant after adjustment for lifestyle factors and BMI, with a hazard ratio of 1.23 for 10 or more years working the night shift compared with none and 1.22 for ever vs never working the night shift (P for trend = .02).

Obesity status did not affect the relationship between night-shift work and diabetes (P for interaction = .12).

However, there was a difference by age: the association between night-shift work and diabetes was stronger in younger vs older women. Among those younger than 50 years, working a night shift for 10 or more years compared with never working this way resulted in a 39% increased risk for diabetes, vs just a 17% higher risk in women aged 50 and older (P for interaction = .028).

Younger women are at lower baseline risk for diabetes and therefore the effect of shift work may be easier to detect in that group, Dr Vimalananda told Medscape Medical News.

Losing Sleep Just One Part of the Equation

Overall, these findings in US black women are similar to those observed in other groups, including the primarily white female population in the Nurses' Health Study, she said.

While the mechanism isn't entirely clear, shift work is associated with disrupted circadian rhythms and overall reduction in sleep duration, both of which can affect metabolism.

Previous studies have also linked circadian misalignment with increased insulin resistance, inflammation, decreased leptin levels, increased glucose and insulin levels, increased mean arterial pressure, and inversion of the normal diurnal cortisol-secretion pattern, the authors explain.

"The mechanisms by which shift work exerts adverse effects on metabolism are likely multifactorial and include multiple neurohormonal [processes]," Dr Vimalananda said.

She and her colleagues also note that there is a high prevalence of shift work among workers in the US; 35% of non-Hispanic blacks work shifts, and so an increased diabetes risk among this group "has important public-health implications."

"Because shift work may be unavoidable, continued research is needed that would help to facilitate circadian adaption to shift work and other sleep disruptions," Dr Vimalananda concluded. "Our group is also investigating certain genetic factors that may modify the association between risk factors such as shift work and incidence of type 2 diabetes."

The Black Women's Health Study is supported in part by the National Institute on Minority Health and Health Disparities and the National Cancer Institute. Support for this study also came from the Department of Veterans Affairs. Dr Vimalananda and coauthors report they have no relevant financial relationships .

Diabetologia. Published online January 11, 2015. Article

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