The Independent
LONDON: Working an occasional night shift for a prolonged period could ultimately kill you, according to a major new study.
Researchers in the US looked at the medical records of about 189 000 women over a 24-year period and found a significant link between “rotating” shift patterns, in which people alternate between night and day work, and coronary heart disease (CHD).
They suggested further work should be done to find out if shift patterns could be altered to reduce the risks.
Scientists have reported the adverse health effects of working night shifts before but the sheer size of this study underlines the extent of the problem.
Dr Celine Vetter, lead author of a paper in the Journal of the American Medical Association (Jama), said: “There are a number of known risk factors for coronary heart disease, such as smoking, poor diet, lack of physical activity and elevated body mass index.
“These are all critical factors when thinking how to prevent CHD. However, even after controlling for these risk factors, we still saw an increased risk of CHD associated with rotating shift work.”
They found that those who worked three or more night shifts a month for a decade had a 15 to 18% higher chance of getting the disease than those who did not have a rotating shift pattern – an effect they described as “modest”.
They said their findings were applicable only to women as occasional shift work might affect men differently.
“It is important to note that this is a modifiable risk factor, and changing shift schedules may have an impact on the prevention of CHD,” said Vetter, an epidemiologist at Brigham and Women’s Hospital in Boston.
“Our results are in line with other findings, yet it is possible that different schedules might carry a different risk – and we have very little information on exact schedules – as well as work start and end times.
“We believe that the results from our study underline the need for future research to further explore the relationship between shift schedules, individual characteristics and coronary health to potentially reduce CHD risk.”
The researchers used information from the US Nurses’ Health Study in which they reported everything from heart attacks to CHD-related chest pain. Fatalities from CHD were confirmed by death certificates.
Over the 24-year period of the study, more than 10 000 women developed the disease.
It has been suggested that changing shifts can disrupt people’s body clock, which operates on a rough 24-hour cycle.
“Circadian misalignment – where the (the body’s natural rhythm is out of step) with behavioural cycles of activity, sleep and food intake – may be a key mechanism linking shift work to chronic disease, including cardiovascular disease,” the researchers wrote in the Jama paper.