Case fatality of myocardial infarction among shift workers

Shift work has been associated with an excess risk of cardiovascular disease (CVD) and more specifically myocardial infarction (MI). The majority of the studies that found a positive association between shift work and CVD have been based on incidence data. The results from studies on cardiovascular-related mortality among shift workers have shown little or no elevated mortality associated with shift work. None of the previous studies have analysed short-term mortality (case fatality) after MI. Therefore, we investigated whether shift work is associated with increased case fatality after MI compared with day workers.

Data on incident cases with first MI were obtained from case-control study conducted in two geographical sites in Sweden (Stockholm Heart Epidemiology Program and Västernorrland Heart Epidemiology Program), including 1,542 cases (1,147 men and 395 women) of MI with complete working time information and 65 years or younger. Case fatality was defined as death within 28 days of onset of MI. Risk estimates were calculated using logistic regression.

The crude odds ratios for case fatality among male shift workers were 1.63 [95 % confidence interval (CI) 1.12, 2.38] and 0.56 (95 % CI 0.26, 1.18) for female shift workers compared with day workers. Adjustments for established cardiovascular risk factors such as diabetes type II and socio-economic status did not alter the results.

Shift work was associated with increased risk of case fatality among male shift workers after the first MI.