Not getting enough sleep has been increasingly associated with a higher risk of chronic conditions like heart disease, diabetes, obesity and certain cancers.

Even worse, new research seems to indicate that how much we sleep could be linked to our ethnicity.

In a recent study, researchers found blacks and Asians don’t sleep as much as whites do. On average, scientists found that white people sleep 7.4 hours per night, Asians and Hispanics sleep 6.9 hours, and black people sleep 6.8 hours.

What’s more, those differences persisted even after sleep-interfering health factors — such as weight and high blood pressure — were accounted for. So what’s going on?

Scientists think environmental and geographical factors are to blame, rather than genes or physical characteristics like variations in facial structure that could interfere with breathing and sleep.

Study researcher Mercedes Carnethon, an associate professor of preventive medicine at Northwestern University, pointed out that blacks and Hispanics tend to live in areas with higher pollution, more city noise and higher crimes rates than whites do, and those can lead to stress-related sleep disturbances.

[Time]