Profs Probe the Science of Sleep

Part four of a four-part series.

For some people, poor sleep may lead to more than just fatigue the next day. Certain sleep disorders may be linked to high blood pressure and other cardiovascular problems.

The health effects of poor sleep are the subject of Daniel Gottlieb’s research, or at least part of it. An associate professor at the School of Medicine and director of the Boston Veterans Administration sleep disorders center, he is participating in one component of a large, long-term study examining the connections between sleep and cardiovascular disease, using data collected through the Framingham Heart Study, a National Heart, Lung, and Blood Institute (NHLBI) epidemiological study begun in 1948 and run by BU since 1971.

In particular, Gottlieb’s study is looking at the effects of the breathing disorder sleep apnea and has found a preliminary relationship between the disorder and cardiovascular disease, particularly hypertension. In the next year or so, as the data come in, Gottlieb says, “we’ll be able to look at whether sleep apnea is an independent predictor of cardiovascular disease.”

Conservative estimates suggest that 2 percent of women and 4 percent of men have the condition. But Gottlieb thinks the numbers are much higher, in the range of 9 percent of women and 25 percent of men, if judged by the nighttime breathing problems alone. “And there’s evidence that it increases with age, so that as the population grows older, there’s likely to be even more,” he says.

The disorder occurs during sleep, when the airway collapses, partially or fully, as people breathe in. The brain, sensing the greater effort to breathe, causes a brief arousal to restore normal breathing, though usually not a full awakening. This happens many times in the night, so people with obstructive sleep apnea usually complain of daytime sleepiness and fatigue, not realizing they have never really gotten into deep sleep.

The connection with higher blood pressure is fairly clear. When blood oxygen levels fall, as they do during sleep when not enough air makes it into the lungs, “there’s a dramatic increase in sympathetic nervous system activity — a surge of adrenalin — and that causes a very abrupt increase in blood pressure,” says Gottlieb. “Ordinarily, at night blood pressure falls, but people with sleep apnea tend not to have that nighttime fall in blood pressure.”

Weight plays a role, too. Fat doesn’t just go to the belly — it’s distributed throughout the body, including the muscles in the airway. That narrows the airway and makes sleep apnea more likely. The good news is that weight loss often improves the disorder. The bad news, Gottlieb says, is that “given the progressive increase in the weight of our population, it’s likely that the prevalence of sleep apnea will continue to rise.” That’s been most dramatic in children. Just as there are more cases of what were previously considered adult diseases, like type 2 diabetes, “similarly we’re seeing obesity-related sleep apnea in children.”

The consequences of sleep apnea aren’t just diseases; there’s also evidence of impairment in memory and other higher cognitive functions, Gottlieb says. “Whether those deficits are due to the impaired attention or whether they exist independent of the effects on attention is something that’s not entirely clear.”

Gottlieb is trying to resolve some of those questions. He is principal investigator at the Boston site of APPLES — the Apnea Positive Pressure Long-term Efficacy Study, sponsored by the NHLBI. Working out of a Brigham and Women’s Hospital–affiliated sleep lab, researchers are doing a randomized control trial of the primary treatment for sleep apnea, using a small machine that delivers continuous positive airway pressure through a mask worn over the nose (or nose and mouth) at night. Some patients in the experiment get the real thing, others a sham version that seems to work but doesn’t, and all take the same cognitive tests.

“There’s good reason to believe that sleepiness is reversible, at least in a significant portion of patients with sleep apnea,” Gottlieb says. “But there is evidence that some of the neurocognitive deficits may not be reversible, and if that’s the case, then that’s an argument for early diagnosis and treatment. Hopefully the study will give us some more insight into the cognitive changes and if they’re reversible with treatment.”

You don’t need to have a disorder like sleep apnea to suffer the effects of poor sleep. Ideally, we’d all get about seven and a half to eight hours a night, Gottlieb says, even though many — maybe most — people don’t. And that’s not good, he says. “There are quite a lot of observational studies suggesting that sleep times shorter than seven hours are associated with a variety of adverse health outcomes. A number of them show increased mortality in short sleepers.” He and his colleagues recently published papers showing association of short sleep time with diabetes and hypertension. “Basically,” he says, “what your grandmother told you was right — you need to get a good night’s sleep.”

Click here to read “Part one: Cracking the circadian code.” Click here to read “Part two: What dreams are made of.” Click here to read "Part three: Helping patients get their Zs."

This article originally ran in the Winter 2006–2007 edition of Bostonia.

Taylor McNeil can be reached at tmcneil@bu.edu.