Black Americans don’t sleep as well as white Americans. That’s a problem.

Bad sleep may fuel health disparities in America.

In America, you can find inequality between white and black people just about everywhere you look. Stark disparities exist in education, in health, in income. And they creep into underappreciated parts of daily life too, like sleep.

Research shows black Americans on average simply don’t sleep as well white Americans do. They don’t sleep as long, they don’t sleep through the night as often, and they suffer more heavily from sleep apnea, a potentially life-threatening disorder. Other minority groups, such as Latinos and Asian Americans, also sleep more poorly than white Americans. But the differences are starkest in black communities.

The sleep gap is essential to understand. It’s a disparity that is both caused by social inequalities and likely to perpetuate them. And that means it could be a ripe target for an intervention that could radically improve millions of American lives. Here are the most important things to know about the black-white sleep gap in America.

Studies consistently find black Americans sleep more poorly than white Americans

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The Centers for Disease Control and Prevention recommends most adults get around seven hours of sleep or more per night. And in a nationally representative study in 2014, the CDC found 33 percent of white Americans reported getting less than that. For black Americans, that figure jumped to 46 percent reporting poor sleep. To put it more simply: Around half of black Americas don’t get enough sleep.

The CDC survey simply had people report how much sleep they were getting. But researchers have also conducted studies where participants have their sleep tracked by Fitbit-like devices called actigraphy bands.

Some of these studies, which track a large number of participants over the course of a week or more, find as much as an hour difference in the average time spent asleep between black and white Americans.

Poor sleep contributes to a vicious cycle of poor health and inequality

Not only do black Americans sleep fewer hours, there’s evidence that the sleep they get is of poorer quality: waking up more frequently and spending less time in the most restful stages of sleep. Black Americans are also more likely to develop sleep apnea, a breathing disorder that can have a serious impact on sleep and health.

When studies control for various socioeconomic factors (like education level), the sleep gap narrows, but it doesn’t disappear completely.

Poor sleep both reflects disparities in America and also likely contributes to them. Living in a poorer, noisier neighborhood with a higher rate of crime is associated with poorer sleep. As is having to work multiple jobs or in overnight shifts (another burden overrepresented in poorer communities).

In turn, it’s suspected that poor sleep can contribute to heart disease, diabetes, and obesity, which also disproportionally affect black Americans.

In the academic literature, short sleep has been associated with higher blood pressure, body mass index, and increased calcification of the coronary artery. In lab experiments, people who slept only five hours a night for one week became less sensitive to insulin, which makes it harder to maintain blood sugar levels. In an overnight sleep study of 1,024 individuals, poor sleep was associated with the misregulation of the hunger hormones leptin and ghrelin, which would explain another finding: that when people are denied sleep, they have increased appetite.

Poor sleep may play a role in a vicious cycle. Poorer health outcomes then negatively impact the economic prospects of black Americans.

This will be a tough problem to solve

The answers here aren’t simple. It’s not yet conclusively known if helping people sleep better would reduce the prevalence of conditions like obesity, diabetes, and heart disease. Poor sleep contributes to and is a risk factor for these conditions, but that doesn’t necessarily mean good sleep would lessen them.

And even if better sleep is the ticket, it’s a huge challenge to get millions to sleep better.

You may have heard experts tout the benefits of good sleep hygiene. For instance, we should put our phones away an hour before bed because their bright light (particularly the blue light) can keep us awake. That’s a useful tip, but stashing away the phone won’t make up for a noisy neighborhood or a house with poor temperature controls. It doesn’t lift the stress of discrimination, which researchers find also plays a role in keeping people up at night. It doesn’t alleviate the jet lag induced by working odd-hour shifts, which can also lead to averse health outcomes.

Education helps too. In 2015, I (Brian) followed a group of NYU researchers who were going out into black communities in New York to screen residents for sleep apnea and encouraging them to get sleep treatment. They would teach community members that even small fixes, like alleviating snoring, can help people sleep more soundly through the night.

But for now, it’s important to recognize that sleep is an indicator of a community’s health, wealth, and overall well-being. And if sleep is disrupted on such a wide scale, it’s indicative of greater disruptions elsewhere.