In the United States, fewer African-Americans are able to get the recommended six to nine hours of sleep per night than people in any other racial group, and what’s more, when African-Americans do get to sleep, less of that sleep is spent in the healthiest “slow-wave sleep,” which is what promotes healing and better cognition.

The effects of this “sleep gap” are felt not only in physical health such as cardiovascular disease and diabetes but in mental health as well.

It’s a gap that goes all the way back to slavery, when sleep deprivation was encouraged by slavers, LA Times‘ Benjamin Reiss. Slaves were often chained together and forced to sleep in cramped quarters, not to mention the fact that female slaves often faced the nighttime terror of assault by white men.

Now, the “sleep gap” is furthered by things like a lack of access to safe neighborhoods, barred access to good schools and good jobs, and a police force and judicial system stacked against African Americans.

Psychologist Tiffany Yip of Fordham University has found in an ongoing study that there is a relationship between discrimination and poor sleep, with instances of discrimination against students in turn leading to poor sleep, which leads to irritability, depression, decreased self-esteem, and a host of other issues.

So discrimination isn’t just affecting our waking lives; it affects our sleeping selves.