The study, published in the U.S. journal JAMA, showed that women who work more than 10 years of rotating night shifts have a 15 to 18 percent increased risk of developing coronary heart disease (CHD), the most common type of heart disease.
There are a number of known CHD risk factors, such as smoking, poor diet, lack of physical activity, and elevated body mass index.
“However, even after controlling for these risk factors, we still saw an increased risk of CHD associated with rotating shift work,” lead author Celine Vetter of the U.S. Brigham and Women’s Hospital said in a statement.
The researchers examined the association between rotating night shift work and CHD, using data from the long-running Nurses’ Health Study I and II, which has followed 240,000 female nurses over a 24-year period.
About 189,000 nurses, who reported their lifetime exposure to rotating night shift work, defined as working at least three night shifts per month in addition to morning and evening shifts, were included in the analysis.
These women also reported on their coronary health, indicating whether they had an angiogram that confirmed CHD-related chest pain, a heart attack, or cardiovascular procedures such as angioplasty, coronary artery bypass graft surgery or stents.
In the case of a self-reported heart attack, or death, information was confirmed by medical records and death certificates to ensure that the event was related to CHD.
Questionnaires also collected data on known risk factors of CHD every two to four years throughout the study period.
Over the 24 year period, more than 10,000 newly developed cases of CHD occurred.
Their analysis indicated that increasing years of rotating night shift work was associated with “a statistically significant but small absolute increase” in CHD risk.
In addition, the researchers also found that recent shift work might be most relevant for CHD risk and that longer time since stopping shift work was associated with decreased CHD risk.
“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,” Vetter said. “We believe that the results from our study underline the need for future research.”