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Longer durations of rotating night shifts linked to small increased risk of CHD
Female registered nurses who work rotating night shifts for 5 years or more may have a small increased risk for CHD, researchers reported in JAMA.
“Shift work, especially shift work that includes night shift, is thought to challenge our circadian system, which regulates physiology and behavior,” Céline Vetter, PhD, instructor in medicine at Harvard Medical School and associate epidemiologist at the Channing Division of Network Medicine, Brigham and Women’s Hospital, told Cardiology Today. “The strain to the system all together with sleep deprivation disrupts the metabolism and increases inflammation, but also puts pressure on social life.”
Vetter and colleagues analyzed data from 73,623 women from the Nurses’ Health Study and 115,535 women from the Nurses’ Health Study II to investigate whether rotating shift work, defined as 3 or more night shifts per month besides day and evening shifts, increased incidence of CHD, including MI, CHD death, angiogram-confirmed angina pectoris, CABG and PCI.
During 24 years of follow-up, 7,303 incidents of CHD occurred in Nurses’ Health Study cohort (mean age at baseline, 55 years) and 3,519 cases of CHD occurred in the Nurses’ Health Study II cohort (mean age at baseline, 35 years).
Longer duration, more risk
According to Vetter and colleagues, increased relative risks were observed after 5 years of rotating shift work or longer. In the Nurses’ Health Study, compared with women without a history of rotating shift work (incidence rates, 425.5 per 100,000 person-years), the incidence rate of CHD per 100,000 person-years for 5 to 9 years of rotating shift work was 525.7 (adjusted HR = 1.12; 95% CI, 1.02-1.22). The incidence rate for 10 years or more was 596.9 (adjusted HR = 1.18; 95% CI, 1.10-1.26; P < .001 for trend). In Nurses’ Health Study II, the incident rate for 5 to 9 years of rotating shift work was 151.6 (adjusted HR = 1.15; 95% CI, 1.01-1.32), and 10 years and more was 178 (adjusted HR = 1.12; 95% CI, 0.99-1.26; P < .001 for trend). Even after adjusting for potential confounders, the association remained in both cohorts (P =.01 for trend).
In the Nurses’ Health Study, the association between shift work and CHD were significantly stronger in the first half of the follow-up as compared with the second half, in which only those who worked shift work 10 or more years had an elevated risk (incidence rate, 556.2; adjusted HR = 1.13; 95% CI, 1.04-1.24), suggesting that recent shift work might be most relevant for CHD risk. Additionally, in the Nurses’ Health Study II, longer duration of time since shift work ended was associated with decreased risk for CHD (P < .001 for trend), suggesting that the CHD risk might wane after stopping working such schedules. This novel finding warrants replication, said Vetter.
Call for research
According to Vetter, future research should focus on two important areas: gaining a better understanding of the specific aspects of schedules that might affect our health most and identifying potential individual characteristics, such as sleep patterns, sleep quality or the individual biological rhythm, that might modify the association between shift work and CHD risk. – by Tracey Romero
Disclosure: Vetter reports no relevant financial disclosures. Please see the full study for a list of all other researchers’ relevant financial disclosures.
For more information:
Céline Vetter, PhD, can be reached at: Channing Division of Network Medicine, Brigham and Women’s Hospital, 181 Longwood Avenue, 4th floor, Boston, MA 02115; email: n2cve@channing.harvard.edu.