Studies keep finding a racial gap, but they don't explain why whites tend to sleep better.
The idea that race or ethnicity might help determine how well people sleep is relatively new among researchers. But in the few short years that epidemiologists, demographers and psychologists have been studying the link, they have repeatedly come to the same conclusion: In the United States, at least, sleep is not colorblind.
Non-Hispanic whites get more and better-quality sleep than people of other races, studies repeatedly show. Blacks are the most likely to get shorter, more restless sleep. What researchers don't yet know is why.
"We're not at a point where we can say for certain is it nature versus nurture, is it race or is it socioeconomics," said Michael Grandner, a research associate with the Center for Sleep and Neurobiology at the University of Pennsylvania. But when it comes to sleep, "there is a unique factor of race we're still trying to understand."
Whatever the cause, doctors say that unlocking the secret to racial sleep disparities could yield insights into why people in some minority groups experience higher rates of high blood pressure, obesity and diabetes.
"When people aren't sleeping as well during the night, they aren't as productive during the day, and they're not as healthy," said Mercedes Carnethon, associate professor of preventive medicine at Northwestern University Feinberg School of Medicine. "It's a self-perpetuating cycle."
Carnethon's study adjusted for risk factors like cardiovascular disease, sleep apnea and obesity. Even so, blacks and members of other minorities, who are statistically more prone to experience such problems, still got less sleep and more disrupted sleep than whites. One obvious remaining culprit, said Carnethon, is socioeconomics.
Moleendo Stewart, 41, who said he has had lifelong sleeping problems, said he did see discrimination as playing a role in his sleep problems. "As a black person in America, even if you succeed in terms of education, you still have to deal with the inherent inequality of society," said Stewart, an administrator for a program for minority students. "I don't blame it on the majority -- that's just simplistic. But in general it's not a fair thing, and you stress because of that."
Sleep experts refer to this as the "autonomy" problem, and studies have shown it has an effect on sleep. "People who feel they have control over their lives were able to feel secure at night, go to sleep, sleep well, and wake up well in the morning and do it all over again," said Lauren Hale, associate professor of preventive medicine at Stony Brook University on Long Island, referring to a study she conducted in 2009.
At least one study suggests that socioeconomic factors affecting sleep are highly specific to race and gender. For example, being divorced or widowed was particularly detrimental to the sleep of Hispanic men, while never being married was more likely to take a toll on the sleep of Asian men. And men of all races who were in relationships slept better than single men; for women, the quality of the relationship was more likely to affect sleep.
The consequences of chronic sleep deprivation for all races include a higher risk of obesity, heart disease, kidney disease, stroke and high blood pressure. "We need to be thinking about sleep the same way we think about diet and exercise," said Grandner.