The most important thing you don't know about sleep

If you think you've heard it all in the case for getting more rest, the impact of sleep on disease may be the ultimate eye-opener.

Despite the laundry list of reasons to log more Z's, most of us are still falling short. “In our society, we don’t value sleep,” says Dr. James Maas, a sleep expert and Equinox health advisory board member. “We think it’s macho to get by on little sleep, but doing so can lead to serious health consequences.” Among them, an increased risk of certain cancers, heart disease, and diabetes, according to a range of scientific studies.

Scientists have been studying the link between lack of sleep and cancer for the last 20 years, says Maas. And while the research is still evolving, one thing is clear: Sleep—and plenty of it—may prevent certain cancers. Recently, researchers at the University of Iceland found that men with snoozing problems (like difficulty falling and staying asleep) were up to two times more likely to develop prostate cancer than those who rested easy. And the more severe their sleeping problems, the greater their cancer risk.

Women who don’t get enough shut-eye are also vulnerable. Regularly sleeping six hours or less each night can increase the risk of breast cancer by 62 percent, according to a study performed by Japanese researchers. And for women who already suffer from the disease, sleeping less than six hours per night can actually result in more aggressive breast cancer tumors, according to a recent study in the journal Breast Cancer Research and Treatment.

Although researchers are still trying to understand the relationship between sleep and cancer, most agree that the hormone melatonin plays a key role. Produced by the brain primarily at night, melatonin helps regulate sleep and wake cycles. Some research suggests that melatonin fights disease by blocking cellular processes that cause cancer growth.

Widen the lens from cancer to illness in general, and you'll find that there's more to the story still. In a study of 30,000 adults, researchers at the West Virginia University School of Medicine discovered that those who sleep less than five hours a night are twice as likely to develop heart disease—and people under the age of 60 and women are at the highest risk. The reason may be that sleep deprivation causes impaired glucose tolerance (a precursor to type 2 diabetes), reduced insulin sensitivity, and elevated blood pressure, all of which increase the risk of artery hardening.

Since not getting enough shut-eye impairs glucose metabolism, it can increase the risk of type 2 diabetes. Researchers at the University of Chicago Medical Center found that just three nights of inadequate sleep made people significantly less sensitive to insulin, which is associated with type 2 diabetes and weight gain. In fact, the decrease in insulin sensitivity was comparable to that caused by gaining 20 to 30 pounds.

Most experts agree that there’s no magic number when it comes to how much sleep you need, although the National Sleep Foundation recommends that healthy adults get between seven and nine hours per night. “Most of us overestimate how much sleep we get,” says Maas. “If you think you’re getting enough, add another hour.” For tips on getting more shut-eye, check out these stories.

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