Contrary to popular myth, most Americans get plenty of sleep: More than eight hours per night on average, according to the most recent Bureau of Labor Statistics. The real problem may be the poor quality of our sleep — and the health problems that can ensue.
A recent study by sleep scientists at the University of California San Diego School of Medicine and elsewhere examined at what happens when healthy men don’t get sufficient “deep sleep.” We asked Dr. Michael Ziegler, professor of medicine and co-author of the study, for a wake-up call.
Q: Why is deep sleep important? How is it qualitatively different from other stages of sleep?
A: During deep sleep, the brain’s electrical activity changes from a rapid chaotic pattern to slow, organized waves called “slow wave sleep.” This produces deep sleep when it is most difficult to awaken someone. We seem to need this slow wave sleep, since we have more of it after sleep deprivation. Slow wave sleep is also called restorative sleep since it restores feelings of being rested and alertness the following day. It also is associated with improved learning and better recall of material we studied the prior day. Slow wave sleep decreases the amount of stress hormones we make, which could make us less likely to develop diabetes.
Q: What’s the connection between deep sleep and hypertension, a risk factor for heart failure and stroke?
A: During deep sleep, we release less adrenaline and noradrenaline so both heart rate and blood pressure decrease, giving our heart and blood vessels a needed rest. We studied patients with sleep apnea who had very disturbed sleep because they were repeatedly aroused by collapse of their airways when they slept. When they used a machine to relieve their sleep apnea, their blood pressure went down. Of course, sleep apnea also interferes with deep sleep, so we wanted to see if loss of deep sleep might cause high blood pressure.
Q: What factors influence a person’s quantity of deep sleep? Your study found that men who have sleep apnea got the least deep sleep. Is sleep apnea the big culprit? Are there other factors?
A: Old age is the most important factor associated with loss of deep sleep. As we age, we have less deep sleep. Some older people get very little deep sleep at night because of sleep apnea, because they do not exercise much, and also just because they’ve aged. We studied some older men in the nationwide MrOs study who had sleep apnea and some who just had little deep sleep, even though they did not have sleep apnea. They all had their blood pressure measured over the following three years. The lack of deep sleep led to high blood pressure much more than did sleep apnea.
Q: What about gender? Is there any reason to suspect the results might be different for women?
A: Women younger than 45 do not develop high blood pressure nearly as often as men do. After menopause, women’s blood pressure increases so that by old age they have as much high blood pressure as men. We studied older men and it is likely that older women would also be more likely to develop high blood pressure if they have too little deep sleep. Although women have less sleep apnea than men, women who do or who snore heavily also have higher blood pressure. That is one of many reasons why it’s important to watch your weight and to exercise.
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