Midday naps and the risk of coronary artery disease: results of the Heinz Nixdorf Recall Study

Abstract

Study objectives: Several studies have assessed the association between midday nap and cardiovascular outcomes and reported heterogenous results. Concern exists that confounding might have distorted these results and contributed to discrepancies among them. This study prospectively examines the association between midday nap habits and the occurrence of coronary artery disease in a non-Mediterranean population.

Participants: The baseline examination of 4,123 participants aged 45-75 years.

Measurements: Measurements included interviews, physical examinations, laboratory tests, and electron beam computed tomography. We studied the influence of midday nap habits on risk of coronary artery disease. We adjusted for several potential confounders including measures of subclinical atherosclerosis-such as coronary calcium score and ankle brachial index-at baseline. Cardiac events during a median follow-up of 8.1 years were defined as nonfatal myocardial infarction and sudden cardiac death.

Results: Overall, 135 of 4,123 subjects (3.3%) either suffered from acute myocardial infarction (81 subjects) or died due to a sudden cardiac death (54 subjects) during follow-up. After adjustment for several confounders including measures of subclinical atherosclerosis, regular long (> 60 min) midday nap was associated with an increased hazard ratio of cardiac events (hazard ratio 2.12, 95% confidence interval 1.11-4.05).

Conclusions: As our detailed confounder analyses showed, confounding is not the sole explanation for this finding. Future research on midday naps should focus on biological mechanisms that may be responsible for increasing the risk of coronary artery disease among subjects taking regular long midday naps.

Figure 1

Frequency of midday naps and median self-reported midday naps durations among 4,123 subjects of the Heinz Nixdorf Recall Study, Germany, 2000–2003. Black bars, men; white bars, women.

Figure 2

Relative frequency of self-reported durations of midday naps among 671 subjects taking at least five midday naps per week, Heinz Nixdorf Recall Study, Germany, 2000–2003. Black bars, men; white bars, women. Subjects with sleep durations > 120 min were collapsed to group 125 min (1.5% of observation).

Figure 3

Estimated probabilities of cardiac events by categories of midday naps adjusted for potential confounders among 4,123 subjects of the Heinz Nixdorf Recall Study, Germany. Midday naps taken ≥ 5 days per week are regular midday naps; regular short midday naps (≤ 1 hour); regular long midday naps (> 1 hour).