A large ongoing study into the health of African-American women has found those who work night shifts are significantly more likely to develop type 2 diabetes than those who never work at night.
In addition, the more years working the night shift resulted in a higher risk and was also more pronounced in younger women than older women.
Previous studies have investigated the link between night shift work and diabetes, including the US Nurses’ Health Study, which largely involve white women.
“Shift work is associated with disrupted circadian rhythms and reduced total duration of sleep”
In the Black Women’s Health Study, 28,041 people provided information in 2005 about working night shift and were followed for the next eight years. During the follow-up period, there were 1,786 incident diabetes cases.
Compared to never having worked the night shift, the increased risk of developing diabetes was 17% for one to two years night shift work, 23% for three to nine years, and 42% for 10 or more years.
After adjustment for lifestyle factors, the association between increasing years of night shift work and increasing diabetes risk remained statistically significant, said the study authors.
Meanwhile, working night shifts for 10 or more years relative to never working the night shift was associated with a 39% higher risk of diabetes among women aged less than 50 years compared with 17% higher risk in women aged 50 years or over.
The authors said: “Even though lifestyle factors and BMI explained a major part of the association of shift work with incident diabetes, women with a long duration of shift work had an increased risk of diabetes after control for those factors, suggesting the presence of additional causal pathways.
“Shift work is associated with disrupted circadian rhythms and reduced total duration of sleep,” they said. “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,” they said.
“In animal models, circadian disruption in susceptible rats led to more rapid loss of beta cell function and increased beta cell death, resulting in decreased beta cell mass, decreased glucose-stimulated insulin secretion and accelerated development of diabetes.”
The study, published in the journal Diabetologia, was carried out by researchers from the Edith Nourse Rogers Memorial Veterans Affairs Medical Center and the Slone Epidemiology Center, both in Massachusetts.