A team including two Howard University professors teased out the peculiar result from responses to one of the nation’s largest health surveys.
Add this to the perils of being black in America: Too little shut eye may not only leave you irritable and groggy—it might also give you high cholesterol. According to a new study led by Girardin Jean-Louis of New York University’s Langone Medical Center, African Americans who habitually sleep less than six hours a day are about 12% more likely to have high cholesterol than those who sleep the recommended seven to eight hours. Curiously, the same study found that sleep deficiency had no such effect on whites.
Jean-Louis collaborated on the study with Chimene Castor and Jenna Gibilaro of Howard University and researchers from the University of South Alabama and the State University of New York’s Downstate Medical Center. The team analyzed the responses of more than 40,000 participants in the 2008-09 US National Health Interview Survey, conducted by the Centers for Disease Control’s National Center for Health Statistics.
The study isn’t the first to tie irregular sleep to hypercholesterolemia, an excess of cholesterol in the blood. Previous studies, however, only linked high cholesterol with oversleeping. Indeed, the new study reinforces that notion, finding that respondents who sleep more than eight hours a day—regardless of ethnicity—are about 30% more likely to report high cholesterol levels than those who sleep seven to eight hours.
But until now the link between inadequate sleep and cholesterol had gone largely unnoticed. The new analysis hints at a reason why: The group didn’t see any correlation between sleep deficiency and cholesterol when they looked at the entire sample group as a whole. Rather, a trend emerged only when they isolated the black respondents. Three years ago, researchers at the West Virginia University School of Medicine found a similar sleep-cholesterol correlation among minorities, but that study lumped all nonwhites into a single category—“Other”—so the correlation couldn’t be tied to any one ethnicity.
The new finding is all the more relevant considering that blacks often don’t get enough sleep. A 2008 study at City College New York found that blacks were 30% more likely than whites to go with five or fewer hours of sleep per day. (To be fair, sleep irregularities appeared to cut both ways: The same study found that African Americans were also more likely than their white counterparts to sleep more than 10 hours per day.)
Given the National Health Interview Survey’s massive scale, the new results are unlikely to be a mere statistical fluke. Participants included adults from all 50 states, of all ages and health profiles, and from the entire spectrum of socioeconomic backgrounds. According to the study’s reported p-value—a rough measure of statistical strength—the odds are less than 1 in 1000 that their results could have occurred by random chance.
Why would sleep shortages cause high cholesterol? It would be premature to assume that they do. It might just as well be that high cholesterol leads to sleep shortages, or that both are a consequence of some third, as yet unknown factor. That said, the researchers note previous studies linking short sleep to increased inflammation, and still other studies linking inflammation to increased levels of the molecules that transport fat and cholesterol through the bloodstream. Lifestyle could also play a part: Participants with high cholesterol were more likely to have hypertension, diabetes, drinking and smoking habits, and other conditions that could hamper sleep.
Either way, one thing’s clear: You shouldn’t sleep on the value of getting a good night’s rest—especially if you’re black.