Much controversy has surrounded the topic of the cardiovascular effects of napping, with various studies yielding mixed results.
For instance, a case-control study of a Greek population found that those who took a nap were at a lower risk of developing coronary heart disease than those who did not. The study appeared in 1988, and it set the tone for much of the ensuing research on napping.
Later, a large cohort study, also of a Greek population, confirmed the findings. It suggested that those who napped regularly had a 37% lower risk of death from coronary heart disease than those who did not nap.
However, studies in other parts of the world — such as Costa Rica, United States, Germany, and Japan — all found higher risks of cardiovascular disease and mortality.
Frequency of naps may be key
Medical News Today reported how the authors of a 2019 paper appearing in the journal Heartset out to settle the controversy. They suggested that not accounting for the frequency of the naps may explain these mixed results. The frequency of napping has been insufficiently studied, the authors argued.
So, they followed almost 3,500 people who had no history of cardiovascular disease over more than 5 years.
The participants reported their napping patterns over the course of a week.
After the follow-up period, 155 fatal and non-fatal cardiovascular events occurred. The analysis accounted for excessive daytime sleepiness (which may have been the result of a sleeping disorder) or obstructive sleep apnea.
The researchers also accounted for age, hypertension, other heart disease risk factors, and the important variables of overall sleep length and physical activity levels (which were missing from the other studies).
The analysis revealed that people who napped 1–2 times a week were 48% less likely to have cardiovascular problems, such as heart attack, stroke, or heart failure, after an average of 5 years follow-up than those who did not nap at all. The benefits were no longer visible for those who napped 6–7 times a week, and the duration of the nap did not seem to make a difference.
First author Nadine Häusler, Ph.D., from the department of internal medicine at Lausanne University Hospital, in Switzerland and her colleagues, concluded at the time:
“Nap frequency may help explain the discrepant findings regarding the association between napping and [cardiovascular disease] events.”