New York - Researchers have found that black women working the night shift are at higher risk of diabetes.
"In view of the high prevalence of shift work among workers in the USA - 35% among non-Hispanic blacks and 28% in non-Hispanic whites - an increased diabetes risk among this group has important public health implications," wrote the study authors from Slone Epidemiology Center at Boston University.
It's important to note, however, that the study wasn't designed to prove that working the night shift can cause diabetes, only that there is an association between the two.
The new research included more than 28 000 black women in the United States who were diabetes-free in 2005. Of those women, 37% said they had worked night shifts. Five percent said they had worked night shifts for at least 10 years, the researchers noted.
Read: Have you been diagnosed with diabetes?
Over eight years of follow-up, nearly 1 800 cases of diabetes were diagnosed among the women.
Compared to never working night shifts, the risk of diabetes was 17% higher for one to two years of night shifts. After three to nine years of night shift work, the risk of diabetes jumped to 23%. The risk was 42% higher for 10 or more years of night work, according to the study.
After adjusting for body mass index (BMI - an estimate of body fat based on height and weight) and lifestyle factors such as diet and smoking, the researchers found that black women who worked night shifts for 10 or more years still had a 23% increased risk of developing diabetes. And those who had ever worked the night shift had a 12% increased risk.
The link between night shift and diabetes was stronger in younger women than in older women. Compared to never working the night shift, working night shifts for 10 or more years increased the risk of diabetes by 39% among women younger than 50 and by 17% among those 50 and older.
Read: Type 1 diabetes can shave a decade off your life
The study was published in the journal Diabetologia.
In the United States, nearly 13% of black women have diabetes, compared with 4.5% of white women, according to the study.
The researchers said finding a higher risk of diabetes even after adjusting for lifestyle factors and weight status suggests that additional factors, such as disruption of the circadian rhythm, may play a role. Circadian rhythms are the body's natural timekeepers, signaling the need for sleep or waking at a certain time.
"Shift work is associated with disrupted circadian rhythms and reduced total duration of sleep. 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," the study authors wrote.
They also said these disruptions can occur even years into a shift work schedule.
The researchers said further study is needed, especially to see if there's a way to better adapt circadian rhythms to shift work. Also, they suggested considering avoiding shift work in favor of other work arrangements whenever possible.
Read more:Why you should keep taking your diabetes medication
Poverty makes diabetes care tougher
Some blood types may raise type 2 diabetes risk