Excess cardiac mortality on Monday: the importance of gender, age and hospitalisation

Background: Available evidence suggests a peak in the incidence of cardiovascular events on Mondays compared to other days of the week. The underlying mechanism may be summarised as naturally occurring rhythmic fluctuations in human physiology, and socially determined rhythms in human behaviour. Change in these rhythms may lead to attenuation of the peak on Mondays. Objective: To quantify the excess risk associated with the Monday peak in cardiovascular mortality and to explore the role of age, gender and hospitalisation. Methods: Details on time and cause of all deaths which occurred in the city of Rotterdam between November 21, 1988 and November 21, 1990 were obtained by sending a questionnaire to the physician who signed the death certificate. We studied the weekly distribution of 1828 confirmed cases of sudden cardiac death, for the group as a whole and in subgroups according to gender, age (< 65 years/65 years) and hospitalisation. Results: The odds ratio (OR) of sudden cardiac death on Monday compared to other days of the week was 1.20 (95% CI: 1.06-1.36). The excess mortality due to the Monday peak amounted to 4.9 per 1000 deaths. The Monday peak was more pronounced in non-hospitalised (OR: 1.25; 95% CI: 1.08-1.44) than in hospitalised patients (OR: 1.06; 95% CI: 0.83-1.37), in men (OR: 1.25; 95% CI: 1.06-1.48) than in women (OR: 1.14; 95% CI: 0.95-1.36), and in those younger than 65 (OR: 1.29; 95% CI: 0.95-1.74) compared to those aged 65 years or over (OR: 1.18; 95% CI: 1.03-1.35). Yet, the confidence limits overlap. Conclusion: The incidence of sudden cardiac death is markedly increased on Monday, more pronounced in non-hospitalised patients. Our results may point to the relevance of naturally occurring rhythmic fluctuations in human physiology, and socially determined rhythms in human behaviour as underlying mechanism.