Napping is a common practice among students, young professionals, and older adults alike. But what are the long-term effects of napping on cardiovascular health? An editorial from the American Heart Association discusses.
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.
Medical News Today reported how the authors of a 2019 paper appearing in the journal Heart set 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.”
In a linked editorial appearing at the time, Yue Leng, Ph.D., and Dr. Kristine Yaffe of the University of California, San Francisco, commented on the findings.
They acknowledged that napping frequency has received insufficient attention from researchers and that daytime napping, in general, is “One of the most common yet understudied sleep behaviors in human beings.”
Entitled To nap or not to nap: more questions than answers, the editorial says that “it remains premature to conclude on the appropriateness of napping for maintaining optimal heart health.”
However, the authors agree that the study led by Häusler and colleagues offers “some reassurance that the answer is probably more than a simple ‘yes’ or ‘no,’ and that we have much more to learn about napping.”
The main point that the authors of the editorial make is that there is currently no “gold standard for measuring naps.”
“The biggest challenge in epidemiological studies of napping is how we define and measure naps. Are they planned or unplanned? What is the purpose of the naps? Are they taken occasionally when needed or habitually as a cultural practice? Are they taken to compensate for insufficient or poor nighttime sleep, or do they indicate underlying ill health? Is nighttime sleep quality taken into account? What is the timing, duration, and frequency of the naps? Do we count in a 5 min ‘dozing-off’ as a nap? What is the best way to measure naps?”
“Until we get to the answers to some of these questions, the implications of napping cannot be fully addressed.”
Researchers could tackle some of these insufficiencies by conducting more comprehensive forms of research, such as meta-analysis and reviews of existing studies. However, these types of research that scientists have conducted so far, also yield contradictory results.
For example, a recent article from the American Heart Association (AHA) entitled “Enjoy your nap, but be aware of the pros and cons” highlights a 2015 meta-analysis that analyzed 11 studies. It found people who nap for an hour or more each day are almost twice as likely to develop cardiovascular disease than those who do not nap.
Commenting on these results, Dr. Clete Kushida, a neurologist and professor of psychiatry and behavioral sciences at the Stanford University Medical Center in California, told the AHA: “We do not know enough about the association of naps with either optimal health or disease risk, especially cardiovascular disease,” adding, “More research needs to be conducted.”
But both Dr. Kushida and Dr. Michael Grandner, director of the Sleep and Health Research Program at the University of Arizona in Tucson, agree that the conditions in which a person takes a nap, and the reasons for it, are key for deciding whether it is beneficial or harmful.
“If you’re napping because it helps you get through the day, that’s probably a good thing,” Dr. Grandner says. “But if you’re napping because you just can’t stay awake, that’s a sign that there’s some underlying health issue. You’re either not getting enough sleep at night, or your sleep quality could be very poor.”
Otherwise, Dr. Grandner says, “A power nap, between 15–45 minutes, can improve memory and reduce fatigue for the rest of the day […] If you’re otherwise well-rested, that kind of nap can actually boost performance pretty well.”
Dr. Kushida agrees: “If an individual has significant daytime sleepiness leading to inadvertent or spontaneous naps, it usually indicates sleep quantity or sleep quality issues.” An assessment of “sleep disorders and or medical diseases” is recommended if the length of time spent sleeping at night is adequate.
In the context of the critical lack of sleep plaguing the U.S., the Centers for Disease Control and Prevention (CDC) highlight some of the health hazards that sleep deprivation can cause.
The CDC found that as many as 1 in 3 U.S. adults are not getting sufficient sleep regularly.
The adverse health outcomes associated with sleep deprivation include heart disease, diabetes, stroke, hypertension, obesity, and depression.
“We live in a culture that doesn’t necessarily value sleep,” Dr. Grandner says. “We need to stop talking about it as unproductive time, and to stop admiring people who brag about how little sleep they think they need.”
“The scientific evidence is there. Sleep is a foundational part of our biology, like diet and physical activity. We need to take care of it.”
– Dr. Michael Grandner