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January 27, 2009

Sleep More, Lower Your BP

The more people sleep, the better the condition of their arteries. The effect seen was equivalent to a 17-point drop in systolic blood pressure.
Sleep is good for you. Even one hour of extra sleep helps prevent coronary artery calcification, according to a recent study. The effect seen was equivalent to a 17 point drop in systolic blood pressure.

Five years after the conclusion of the study, 27% of the participants who slept less than five hours a night had developed coronary artery calcification.

People don't get enough sleep. Everyone knows this. A team at the Chicago Medical Center set out to specifically assess the effects of sleep on calcification of the arteries, a predictor of future coronary heart disease. To their surprise, they found that the more people slept, the better the condition of their arteries was. Five years after the conclusion of the study, 27% of the participants who slept less than five hours a night had developed coronary artery calcification. This figure dropped to 11% for those who slept five to seven hours a night and continued to fall to 6% for those who slept more than seven hours a night. The study also suggested a slightly stronger benefit of sleep for women than for men.

Other recent studies have suggested that sleep deprivation may be a risk factor for many common medical problems, including weight gain, diabetes and hypertension. The exact reason for this is not known. Diane Lauderdale, director of this study and associate professor of health studies at Chicago University Medical Center, agrees that the reason for the observed benefits of sleep on calcification is indeed a mystery. She speculates that the fact that people's blood pressure decreases while sleeping and that production of the stress hormone cortisol declines in those who get more sleep may somehow be involved. She also allows that it is just as likely that some as yet unidentified factor is responsible for the effect.

The moral of the story? If you're not one of those lucky people who are able to sleep on the job, it's in your best interests to figure out a way to get an additional hour of sleep at home. Dr. Lauderdale recommends at least six hours of sleep a night. Although this correlational study does not prove that short sleep leads to coronary artery disease, it certainly hints at it.

The research focused on 495 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study, which was begun in 1985. The sleep study itself began in 2001; participants were 35-47 years old. Each subject's sleep duration was measured using wrist actigraphy, a motion sensor worn like a wristwatch, to estimate sleep duration over six nights. Unlike older methods of sleep measurement, wrist actigraphy does not appear to alter sleep behavior. Participants also kept sleep logs and filled out sleep questionnaires. Buildup of arterial calcium was measured using electron beam computed topography scans. Two scans were taken, one at the study's start and a second five years later. All results were adjusted for age, sex, race, education, smoking and apnea risk.

The results were published in the December 24/31, 2008 issue of the Journal of the American Medical Association (JAMA).

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