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Data from the multinational Prospective Urban Rural Epidemiology (PURE) cohort study support a J-shaped curve for sleep duration vs risk of death and cardiovascular events, with 6-8 hours per day appearing optimal but without a clear risk for those getting less than 6 hours.

Sleeping 9-10 hours per day was linked to significantly higher risk for a composite of all-cause mortality and major cardiovascular events (HR 1.17, 95% CI 1.09-1.25), with >10 hours of sleep per day tied to an even higher risk (HR 1.41, 95% CI 1.30-1.53), reported Salim Yusuf, MD, DPhil, of McMaster University in Hamilton, Ontario, and colleagues in the .

The researchers found a nonsignificant trend toward increased risk with daily sleep of 8-9 hours (HR 1.05, 95% CI 0.99-1.12).

But, contrary to findings of several previous studies, risk for the composite endpoint in individuals sleeping less than 6 hours per day also did not reach statistical significance in the huge study (HR 1.09, 95% CI 0.99-1.20).

The researchers assessed PURE participants (ages 35-70) in 21 countries with varying income levels. Using self-reported information, the investigators approximated the length of daily sleep and daytime naps according to the amount of time in bed and napping time.

PURE is an ambitious longitudinal study that collected wide-ranging data from more than 100,000 people, and included diet and other lifestyle factors as well as their health outcomes. Previous analyses had focused on diet -- showing, for example, that whole-fat dairy intake was associated with lower cardiovascular risk. Participants received an in-person physical and interview at baseline and were contacted at least every three years by local investigators for follow-up.

Of 116,632 participants included in the current analysis (all having at least one follow-up contact), 7,342 participants died or had major cardiovascular events, which included fatal cardiovascular incidents and non-fatal myocardial infarction, stroke, and heart failure. Specifically, there were 4,381 participant deaths and 4,365 participants that had major cardiovascular events. Median follow-up was 7.8 years.

Another finding was that daytime napping was linked with a greater risk of major cardiovascular events or death among participants who slept for >6 hours each night, but not among those who slept for <6 hours each night, researchers found.

Prior research has found that excessive sleep puts people at an increased risk of cardiovascular disease or death, while other papers have shown contradictory findings. There were meta-analyses performed, but the findings were less convincing because study types varied, there were diverse target populations, variations in reference groups, and broad definitions of sleep durations. Many of the studies were from North America, Europe, Japan, and China, the investigators emphasized.

Sleeping longer is often thought of as a healthy habit. The American Academy of Sleep Medicine and the Sleep Research Society suggests that ≥7 hours per night of sleep is ideal, noted Dominik Linz, PhD, of Royal Adelaide Hospital in Australia, and coauthors in .

"It remains unclear whether excessive sleep duration or daytime napping may expose individuals to greater risk of death and CV disease," the editorialists wrote, adding that the current study "provides important epidemiological information" but leaves much still unanswered. The details of sleep architecture and the reasons for daytime napping are important in determining the causal factors that may be at work, they suggested.

When it comes to practice, clinicians should advise their patients to "try to get 7 or more hours on average," commented Kim Eagle, MD, of the University of Michigan Samuel and Jean Frankel Cardiovascular Center in Ann Arbor, who was not involved in the study. "Nap if it feels like it invigorates. Brief power naps may help people who have restless sleep at night."

Many factors influence an individual's sleep, he said. A partial list includes heat, stress, underlying medical illnesses, nutrition, activity, and alcohol use.

"Also, as we age, our sleep generally gets to be a bit less effective. Therefore, we need more time spent sleeping to get the same revitalization that sleep provides. This age relationship to our sleep and the types of sleep is not often understood by patients and they find it frustrating," Eagle told 名媛直播.

This study has "huge limitations," he cautioned, noting that it's a difficult subject to study, especially with self-reported data.

In their editorial, Linz and colleagues wrote, "Further sleep intervention studies including objective and long-term tracking of the dynamic nature of sleep duration and napping habits are warranted to assess whether sleep patterns represent a risk marker or a modifiable CV risk factor."