Just one extra hour of sleep a day appears to lower the risk of developing calcium deposits in the arteries, a precursor to heart disease, U.S. researchers said on Tuesday.
The finding adds to a growing list of health consequences — including weight gain, diabetes, high blood pressure — linked to getting too little sleep.
"We found that people who on average slept longer were at reduced risk of developing new coronary artery calcifications over five years," said Diane Lauderdale of the University of Chicago Medical Center, whose study appears in the Journal of the American Medical Association.
"It was surprisingly strong," Lauderdale said in a telephone interview.
Calcium deposits in the coronary arteries are considered a precursor of future heart disease. "It's a very early marker of future risk," she said.
Unlike other studies looking at the risks of getting too little sleep, which use people's own estimates of their sleep patterns, Lauderdale's team set out to measure actual sleep patterns.
They fitted 495 people aged 35 to 47 with sophisticated wrist bands that tracked subtle body movements. Information from these recorders was fed into a computer program that was able to detect actual sleep patterns.
The team used special computed tomography, or CT, scans to assess the buildup of calcium inside heart arteries, performing one scan at the start of the study and one five years later.
After accounting for other differences such as age, gender, race, education, smoking and risk for sleep apnea, the team found sleep duration appeared to play a significant role in the development of coronary artery calcification.
About 12 percent of the people in the study developed artery calcification during the five-year study period. Among those who had slept less than five hours a night, 27 percent had developed artery calcification.
That dropped to 11 percent among those who slept five to seven hours, and to 6 percent among those who slept more than seven hours a night.
Lauderdale said it is not clear why this difference occurred in people who slept less, but they had some theories. Because blood pressure tends to fall off during sleep, it could be that people who slept longer had lower blood pressure over a 24-hour period.
Or, it could be related to reduced exposure to the stress hormone cortisol, which is decreased during sleep.
Or it may be some unidentified process.
"It's something of a mystery," Lauderdale said.
Kathy Parker, a sleep researcher from the University of Rochester's School of Nursing in New York, said the study underscores the role sleep plays in health.
"People think that sleep doesn't matter but clearly it does. Sleep deprivation is a public health problem and studies such as this show how increasing sleep duration can have tremendously positive effects," Parker, who was not involved in the research, said in a statement.
Lauderdale said her findings should be confirmed by others, but said many studies point to the need for at least six hours of sleep a night.
