Moleendo Stewart can’t say for sure what’s caused his lifelong sleeping problems. But he has his suspicions.
There’s the childhood spent in loud, restless neighborhoods in Miami. “You hear people shooting guns all night, dealing drugs,” said Mr. Stewart, 41, who lives in the East Flatbush section of Brooklyn. He also cites his weight, 260 pounds, down from a peak of 310.
Sleep experts would point to another factor working against Mr. Stewart: He is a black man.
The idea that race or ethnicity might help determine how well people sleep is relatively new among sleep 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 Dr. Michael A. 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 ofhigh blood pressure, obesity and diabetes. Helping poor or immigrant populations to get more solid sleep, they say, could also help break the cycle of poverty and disadvantage.
“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 Dr. Mercedes R. Carnethon, associate professor of preventive medicine at Northwestern University Feinberg School of Medicine. “It’s a self-perpetuating cycle.”
The latest evidence that race and ethnicity can affect sleep came in June at the annual meeting of the Associated Professional Sleep Societies, held in Boston. In one of two studies on the topic presented there, white participants from the Chicago area were found to get an average of 7.4 hours of sleep per night; Hispanics and Asians averaged 6.9 hours and blacks 6.8 hours. Sleep quality — defined as ease in falling asleep and length of uninterrupted sleep — was also higher for whites than for blacks.
While those findings are consistent with earlier studies, this one, led by Dr. Carnethon, 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 and more disruptive sleep than whites.
One obvious remaining culprit, says Dr. Carnethon, is socioeconomics.
Because Chicago is still a fairly segregated city, “the blacks and Hispanics in our study were generally living in neighborhoods that are closer to freeways, so you have freeway noise, there’s more business noise at night, and there’s potentially more crime, which is stressful to people,” Dr. Carnethon said. People in lower-income neighborhoods are also more likely to have multiple jobs or to work odd hours, which can interfere with sleep.
The idea that differences in work and living conditions can explain the racial sleep disparities is a popular one among sleep experts. But studies that have accounted for those factors suggest a more complex reality.
One such study from 2005 — also taking place in Chicago — measured sleep among 669 participants while adjusting for education, income and employment status. In the end, black men on average still slept 82 minutes less per night than white women, who were found to sleep the best of anyone in the study.
Of course, isolating the real-life effects of social inequality can be tricky. “There are more subtle differences” among people than income and education, said Dr. Kristen Knutson, assistant professor of medicine at the University of Chicago and an author of the study. “We had no way to control for stress, and there are social stresses an African-American man might feel that a white man with the same income and education level wouldn’t.”
Mr. Stewart, the Brooklyn resident, 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 Mr. Stewart, an administrator for a program that exposes students in racial minorities to careers in science and math. “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 Dr. Lauren Hale, associate professor of preventive medicine at Stony Brook University on Long Island, referring to a study she conducted in 2009. “That’s part of the cycle not just for blacks and minorities, but other disadvantaged populations.”
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. Asian women lacking in education were more likely to report sleep problems than similarly educated white women. And men of all races who were in relationships slept better than single men, regardless of relationship quality; for women, the quality of the relationship was more likely to affect sleep.
“There’s an effect of socioeconomics,” said Dr. Grandner, a lead author of the study, “but it’s not really the economic. It’s more about the socio.”
It may also be the culture. Black and Hispanic children in America are far less likely to have regularly enforced bedtimes than white children, according to a 2010 study conducted by Dr. Hale for the National Institutes of Health. White children were also more likely to have “language-based” bedtime routines — those that involve reading or storytelling — both of which are associated with a wide range of cognitive and behavioral advantages.
These routines establish patterns that can last a lifetime, Dr. Hale said. “If routines are absent, especially these language-based routines, then children may be missing out on opportunities to develop and sleep optimally,” she said.
And some researchers aren’t ready to discount biology. In a forthcoming study, Dr. Grandner found that short sleepers are more likely to have elevated levels of C-Reactive protein, but how much depended on race. C-Reative Protein is produced by the body when inflammation is present and has previously been implicated in sleep problems.
The consequences of chronic sleep deprivation for all races include a higher risk of obesity, heart disease, kidney disease, stroke and high blood pressure. Other insidious threats — like depression, mood swings and decreased learning capacity — have all been linked to lack of sleep, both as consequences and causes. In order to break the cycle, researchers say, patients need to make sleep a priority.
“There’s this idea in this country that sleep might not be the most important thing, that we have to get things done and sleep can be de-prioritized,” said Dr. Grandner, comparing America with European countries that carve out midday periods for sleep. “We need to be thinking about sleep the same way we think about diet and exercise.”