Background: The siesta (afternoon nap or rest), a common traditional behaviour in tropical areas, may increase the risk of myocardial infarction (MI) since the post siesta cardiovascular response very closely resembles the period soon after waking up in the morning when the onset of acute cardiovascular events is high.

Methods: We studied 505 MI survivors and 522 randomly selected controls, matched for age, gender, and area of residence, in a population-based case-control study in Costa Rica. Participation rates were 97% for cases and 90% for controls. All subjects completed a physical activity questionnaire that included occupational and leisure time components with specific questions on siesta. Five siesta frequency categories (<1/wk, 1–4/wk, 5–6/wk, daily [≥1 h and <2 h], and daily [≥2 h and <3:30 h]) were used to calculate the odds ratio (OR) by multiple logistic regression.

Results: Compared to controls, cases were more likely to take daily siestas (44 versus 35%, P = 0.01), and spend more time per siesta (1:07 ± 0:04 versus 0:54 ± 0:04 h:min, P = 0.002). As compared to subjects with the lowest siesta frequency (<1/wk), the OR for MI among those in the highest category was 1.51 (95% CI : 1.02–2.25, P for trend = 0.006). After adjusting for risk factors, lifestyle, and health history the OR across the siesta categories were 1.0, 0.77, 1.28. 1.66, and 1.40 (P for trend = 0.02).

Conclusions: Our data suggest that the practice of daily siesta is associated with increased risk of MI.