Shift Work and 11-year Progression of Carotid Atherosclerosis in Middle-Aged Finnish Men

INTRODUCTION:  Inconsistent associations between shift work and cardiovascular disease (CVD) as reported in the literature might be partly due to health-related selection out of certain work schedules. We, therefore, studied the relationship between different work schedules and progression of carotid atherosclerosis, an asymptomatic early indicator of CVD.

METHODS:  We studied 621 men, aged 42-60 years, in the prospective Kuopio Ischemic Heart Disease Risk Factor Study cohort. Using multiple linear regression models adjusting for 21 covariates, we evaluated the associations of baseline work schedules with 11-year progression of ultrasonographically assessed carotid intima-media thickness (IMT) and how these associations varied by preexisting CVD status.

RESULTS:  Standard daytime work, daytime work including weekends, evening/night/rotating shifts, or other shifts were associated with 31%, 38%, 32%, or 34% 11-year increases in IMT, respectively. Compared to standard daytime workers, daytime workers who also worked during weekends (worked more than 5 days per week) experienced a faster progression of carotid atherosclerosis [relative change ratio (RCR)=1.06, 95% CI: 1.01-1.10, P=0.008)]. This association was higher among men who had prior ischemic heart disease (RCR=1.13, 95% CI: 1.02-1.24, P=0.016). Men with preexisting carotid artery stenosis also experienced a higher IMT progression (RCR=1.10, 95% CI: 1.02-1.19, p=0.017).

CONCLUSIONS:  Daytime work including weekends appears to accelerate the progression of carotid atherosclerosis compared to standard daytime work among middle-aged Finnish men, especially among those with pre-existing CVD. We could neither demonstrate nor rule out any association between other work schedules and progression of carotid atherosclerosis.