The evidence continues to mount on the health benefits of adequate sleep. A new study published this week in the Journal of the American Medical Association finds that sleeping less than seven and a half hours a day may be associated with a greater risk for heart disease, particularly for those whose blood pressure spikes overnight.
"Sleep habits have a huge impact on human health," says the study's lead author, Dr. Kazuo Eguchi of Jichi Medical University in Tochigi, Japan. Past studies have linked improper sleep habits sleeping either too little or too much to disorders such as obesity and diabetes as well as a higher risk of heart attacks and premature death. (See TIME's A-Z Health Guide.)
Eguchi's study examined the connection between sleep and heart disease among elderly people. Over a 50-month period, researchers monitored 1,225 people with an average age of 70 and a history of hypertension. For the duration of the study, participants recorded their nightly sleep habits in a sleep diary; their blood pressure was monitored all day and night, using an ambulatory blood pressure monitor, a small halter-like device that takes readings every 30 minutes 24 hours a day. Cardiovascular events including stroke, heart attack and sudden cardiac death were tracked among the participants.
The study found that 99 cardiovascular events occurred among all volunteers. The incidence rate was about 33% higher among people who slept less than seven and a half hours a night and had elevated overnight blood pressure the so-called "riser pattern" compared with longer sleepers. But those who slept less than seven and a half hours a night yet experienced no overnight hypertension showed no increased cardiac risk; their rate of heart disease was the same as that of the long sleepers. Particularly when it comes to elderly patients, the authors write that "physicians should inquire about sleep duration in the risk assessment of patients with hypertension."
"Sleep is important [for everyone], from children to the elderly," Eguchi says. "But it is more important when someone has some cardiovascular risk factors like hypertension."
Normally, blood pressure drops during sleep, but if people don't get enough shut-eye, it can exacerbate hypertension or even cause it and lead to depression and weakened immunity, according to previous research. Longer sleep is, therefore, especially vital for patients who already have high blood pressure. Maintaining a consistent sleep pattern is also important tampering with the body's circadian rhythm is associated with a variety of hormonal, metabolic and cardiovascular problems. In late October, Swedish researchers reported that the rate of heart attacks jumped following daylight savings time shifts in the spring and fall. "Our data suggest that vulnerable people might benefit from avoiding sudden changes in their biologic rhythms," Dr. Imre Janszky of the Karolinska Institute in Stockholm wrote.
Research generally suggests that seven to eight hours sleep a night is optimal for adults. Eguchi says his study underscores the special need for elderly, hyptertensive patients to get a good night's sleep. "It's a very important issue in their health," Eguchi says, adding that still more studies need to be done to differentiate between "good" and "bad" sleep. The participants in his study recorded the duration of sleep, but not the quality for instance, whether they experienced disturbances or nocturnia, the medical term for the need to get up and urinate at night, a common condition among the elderly.
Probing further into the nature of sleep, say researchers, may help determine the precise benefits of sleep largely still a mystery regardless of age or medical condition.