In this study, the men averaged 11.2 percent of slow-wave sleep, she said. Those in the lowest of the four groups averaged only 4 percent or less. Other studies have shown that slow-wave sleep is lower in older men than in women.
While the study found an association between slow-wave sleep and high blood pressure, it did not prove a cause-and-effect.
The new research adds to information about the importance of sleep, said Dr. Alberto Ramos, co-director of the University of Miami Sleep Disorders Center.
Experts agree, he said, that not enough sleep, over time, can boost the risk of high blood pressure.
The new study, he noted, goes further by suggesting that "the quality of your sleep, specifically the amount of deep sleep, is as important in your overall health -- or at least in developing high blood pressure -- as the actual amount of time you sleep."
Exactly why this is so is not known for sure, according to Redline and Ramos.
"When you go to sleep, blood pressure normally falls," Redline said. "A lot of that fall occurs during slow-wave sleep." When that typical drop in night-time pressure is affected by a lack of deep sleep, "it may set you up for daytime elevations," she added.
Ramos agreed that might explain the link.
Adults can take measures to try to increase slow-wave sleep, Redline said. "Anything that wakes you up repeatedly will disrupt your slow-wave sleep," she noted.
Getting treated for underlying disorders that can wake you up -- such as sleep apnea -- could help, she said.
The take-home message, Ramos said, is to pay attention to sleep quality, not just the length of your sleeping hours. Even though the link between low deep sleep and high blood pressure held after taking weight into account, Ramos noticed those in the lowest deep-sleep groups also tended to be heavier than the others. Avoiding obesity would be a good idea, he said.
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