The aim of this review was to assess the risk of cardiovascular disease (CVD) events associated with shift work and determine if there is a dose/response relationship in this association.
Electronic databases were searched for cohort or case-control study designs in any population, reporting exposure to shift work as the main contributing factor to estimate CVD risk. For each study, adjusted relative risk (RR) ratios and 95% confidence intervals were extracted and used to calculate the pooled RR using random-effect models. Metaregression analysis was conducted to explore potential heterogeneity sources. Potential nonlinear dose/response relationships were examined using fractional polynomial models.
Twenty-one studies were included with a total of 173,010 unique participants. The majority of the studies were ranked low-to-moderate risk of bias. The risk of any CVD event was 17% higher among shift workers than day workers. The risk of coronary heart disease (CHD) morbidity was 26% higher. Subgroup analysis showed an almost 20% higher risk of CVD and CHD mortality among shift workers than those who did not work shifts. After the first 5 years of shift work, there was a 7.1% increase in risk of CVD events for every additional 5 years of exposure. Heterogeneity of the pooled effect size estimates was high, and metaregression analysis showed that sample size explained 7.7% of this.
The association between shift work and CVD risk is nonlinear and seems to appear only after the first 5 years of exposure. As shift work remains crucial for meeting production and service demands across many industries, policies and initiatives are needed to reduce shift workers’ CVD risk.