Female registered nurses who work a rotating night shift for 5 years or more have a slightly higher risk of heart disease, according to a new study published in JAMA.
Shift work can disrupt social and biological rhythms, which may increase the risk of chronic disease.
The National Sleep Foundation list a number of conditions that people who work shifts are more likely to experience, including cancer, metabolic disease, ulcers, and obesity, not to mention depression and reduced performance due to disrupted circadian rhythms.
Previous studies have suggested an association between shift work and coronary heart disease (CHD), cancer, and metabolic disorders.
However, results from prospective studies linking shift work to CHD have been inconsistent, and they have been limited by short follow-up.
Celine Vetter, PhD, of Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, and colleagues examined the incidence of CHD in 189,158 initially healthy women.
The participants were followed up over 24 years in the Nurses’ Health Studies (NHS), carried out from 1988-2012 and 1989-2013.
The researchers determined the lifetime history of rotating night shift work, defined as three night shifts or more per month in addition to day and evening shifts.
During follow-up, there were 7,303 incidents of CHD in the first NHS and 3,519 in the second.
Results suggested that the longer a nurse carried out rotating night shift work, the higher the chance of CHD. Less than 5 years of shift work does not appear to increase the chance of CHD, but working shifts for more than 5 years is linked with a statistically significant increase.
However, the authors point out that since the risk only affected those who worked 5 years or more on rotating night shifts, and this was only 15% of all the participants, the absolute risk and public health impact of night work is relatively small.
There was evidence that the risk decreased after quitting shift work, and the longer the time lapse since quitting, the smaller the chance of CHD.
The authors also looked at whether shift work was associated with increased CHD risk in the absence of hypertension, hypercholesterolemia, and diabetes. The first NHS suggested a link but the second did not, implying that shift work entails a risk even in those without prior susceptibility.
The authors conclude:
“Further research is needed to explore whether the association is related to specific work hours and individual characteristics.”