Researchers find that sleep deprivation or excess in women may be associated with increased risk of coronary artery disease

Solid eight hours is great, more than nine not so fine

Monday, January 27, 2003

Researchers at Brigham and Women’s Hospital (BWH) have found that both long and short sleep durations may be independently associated with an increased risk of heart disease in women. These findings are published in the January 27, 2003 issue of the Archives of Internal Medicine.

"There have been several studies examining the impact of short duration sleep deprivation, however, our research is one of the first to hypothesize that sustained reduced sleep duration as well as an excess could negatively impact a woman’s cardiovascular health," said Najib Ayas, MD MPH, of BWH. "Our data reflects that short and long sleepers may be at a higher risk of coronary heart disease (CHD)."

Dr. Ayas and his team found that sleeping five hours or less per night was associated with a 30 percent increase in risk of CHD and sleeping six hours per night was associated with an 18 percent greater risk. Women who slept eight hours per night had the lowest recorded rate of CHD.

Chronic sleep deprivation is common in today’s society. It is reported that a third of Americans sleep six or less hours per day. Previous research has shown that the effects of short-term reduced sleep duration include increased blood pressure, heart rate variability, decreased glucose tolerance and increased cortisol levels. Yet, little is known about how the duration of sleep impacts long-term health outcomes, such as one’s risk of CHD, the number one killer of both men and women in the U.S. CHD, caused by the narrowing of the coronary arteries and a common catalyst for heart attacks, is greatly influenced by a variety of lifestyle choices, such as exercise, smoking and diet. BWH researchers have now revealed sleep may weigh into that equation, too.

In a ten-year period, 934 cases of CHD (myocardial infraction) were reported among 71,617 women participating in the BWH-based Nurses’ Health Study. The women were asked to self-report on their sleeping patterns and a variety of health and lifestyle factors.

"Our study suggests that curtailing sleep may have adverse cardiovascular consequences," said Ayas, also of Harvard Medical School. "This research sends an important message to a population that is spending more and more time working and staying up late watching television or using the internet. Adequate daily sleep should not be considered a luxury, but an important component of a healthy lifestyle."

Overall, the research establishes an important link between sleep and cardiovascular health, although more research is required to better understand the biological mechanisms underlying this correlation. With prior knowledge about the debilitating influence of short-term sleep deprivation, the association revealed between chronic sleep deprivation and increased risk of CHD was consistent with research team’s original hypothesis. However, unexpectedly, the data also showed that increased sleep duration - nine or more hours of sleep - was also associated with an increased risk of CHD. In this study, among the five percent of women who slept on average nine to 11 hours, there were 59 reported cases of CHD. These women were 38 percent more likely to suffer from CHD than women who slept eight hours a night. The reason for the positive relationship between increased sleep duration and CHD remains elusive at the present time.

"While further investigation will pinpoint the causes, we now know that the quantity of sleep women are getting - whether it is too much or too little - seems to be an important factor in maintaining a healthy heart," noted Ayas.

The Nurses Health Study (NHS) was initiated in 1976 at Brigham and Women’s Hospital. It is the longest major women’s health study ever undertaken and has resulted in hundreds of journal articles, many containing groundbreaking findings on how to prevent some of the major causes of disease and death in women.

The study was supported by grants from the American Heart Association.

BWH is a 716-bed nonprofit teaching affiliate of Harvard Medical School and a founding member of Partners HealthCare System, an integrated health care delivery network. Internationally recognized as a leading academic health care institution, BWH is committed to excellence in patient care, medical research, and the training and education of health care professionals. The hospital’s preeminence in all aspects of clinical care is coupled with its strength in medical research. A leading recipient of research grants from the National Institutes of Health, BWH conducts internationally acclaimed clinical, basic and epidemiological studies.

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