Taking a daytime nap once or twice a week, but not more often, is associated with a lower risk of cardiovascular disease “events,” such as heart attacks, heart failure and strokes, according to a study published in the journal Heart.
No association was found, however, between the length of the naps and the risk of cardiovascular disease events.
While interesting, these findings shouldn’t cause anybody to worry about not being a nap-taker. The study comes with plenty of caveats, including a great big one: It is observational, which means it can’t prove cause and effect.
Still, the study’s findings offer an interesting addition to the ongoing debate about whether napping is good for heart health. Previous research has produced conflicting results. Most of those earlier studies, however, tended to distinguish only between nappers and non-nappers. They didn’t take the frequency of napping into account. Most also examined the effect of napping only on fatal cardiovascular events.
The authors of the current study — a team of researchers led by Dr. Nadine Hausler of the University Hospital of Lausanne, Switzerland — wanted to see if they could address those and other unanswered questions.
How the study was done
For the study, the researchers analyzed data collected from 3,462 Swiss adults, aged 35 to 75, who were participating in a larger ongoing research project investigating possible risk factors for cardiovascular disease. None had a history of cardiovascular disease when they entered the study.
At the study’s start, the participants filled out a detailed health questionnaire, which included questions about how often they had napped within the previous week and how long the naps had been. More than half (58 percent) of them reported that they hadn’t napped during the previous week. One in five (19 percent) said they had taken one to two naps, while about one in 10 (12 percent) said they had taken three to five naps, and a similar proportion (11 percent) said they had taken six to seven naps.
The naps ranged in length from five minutes to an hour or more.
The participants were then followed for up to 7.8 years, with a median follow-up of 5.3 years. During that period, there were 155 fatal and non-fatal cardiovascular events.
The researchers analyzed the data for associations between the participants’ napping habits and their risk of having a cardiovascular event. They found that the people who reported napping one to two times a week were almost half as likely to have experienced a heart attack, stroke or heart failure during the study period than the non-nappers.
The analysis revealed no difference in risk between the non-nappers and those who reporting napping more than two times a week. Nor was any association found between nap length and the risk of a cardiovascular event.
Those findings held even after the researchers adjusted the data for factors known to influence the risk of cardiovascular disease, such as age, high blood pressure, depression and duration of sleep at night.
The only factors that changed the results were being older than 65 and having severe sleep apnea. Among those groups, napping one to two times a week was not associated with a lower risk of having a heart attack, stroke or heart failure.
Older people, the researchers point out, may take naps because of underlying health issues — a factor that likely weakens any role than napping has on their risk of a cardiovascular disease event.
Limitations and implications
In addition to being observational, this study relied on the participants’ self-reports on how often and how long they napped. Such reports can be inaccurate. The study also involved a relatively low number of people — a factor that may have affected the results.
Still, the study’s results are intriguing, particularly as they are in line with those of several previous studies. The explanation for such findings is unclear, however, although the current study’s authors speculate that “occasional napping might be a result of a physiological compensation allowing for a decrease in stress due to insufficient nocturnal sleep and thus could have a beneficial effect on [cardiovascular disease] events.”
But much more research is needed before we truly understand what role, if any, naps play in heart health.
In an editorial that accompanies the study, Drs. Yue Leng and Kristine Yaffee of the University of California, San Francisco, point out that this study — and other research on this topic — is hindered by a lack of a gold standard for defining and measuring naps.
“Are they planned or unplanned?” they ask. “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 night-time sleep, or do they indicate underlying ill health?”
“Until we get to the answers to some of these questions, the implications of napping cannot be fully addressed,” they stress.
FMI: You can read the study and the editorial on Heart’s website.