How glued are you to the main screen in your life? Very, if you’re like most of us; survey data suggests that Americans collectively check their phones 8 billion times each day.

All of that smartphone screen time is likely taking a toll on our sleep, according to a new study published in the journal PLOS ONE. People who used their phones more, especially around bedtime, got less and worse sleep than their peers.

That’s concerning, says Dr. Gregory Marcus, one of the study’s authors and director of clinical research for the division of cardiology at University of California, San Francisco. “There’s growing evidence that poor sleep quality is not simply associated with difficulty concentrating and being in a bad mood the next day,” he says, “but may be a really important risk factor to multiple diseases.”

For the 30-day study, 653 adults all across the country downloaded an app that ran in the background of their phones and monitored screen time. The people in the study recorded how long and how well they slept, following standardized sleep scales.

People interacted with their phones about 3.7 minutes per hour, and longer screen activation seemed to come at a detriment. “We found that overall, those who had more smartphone use tended to have reduced quality sleep,” Marcus says.

The study doesn’t prove that using screens more causes worse sleep. (In fact, it might be the other way around: “We can’t exclude the possibility that people who just can’t get to sleep for some unrelated reason happen to fill that time by using their smartphone,” Marcus says.) But other research supports the idea that screens work against slumber. Some data suggests that the blue light your phone emits suppresses melatonin, a hormone that helps the human body maintain healthy circadian rhythms. “We also know that emotional upset, or just being stimulated apart from smartphone use, can adversely affect sleep quality, and that engaging with Twitter or Facebook or email can cause that sort of stimulation,” Marcus says.

Reactions to extended screen time might vary from person to person. But if you have difficulty falling asleep or getting good sleep, look to your smartphone, Marcus says. “Because sleep quality is so important, I think it’s useful for individuals to take these data and at least give avoidance of their smartphones an hour or so before they go to bed a try to see if it helps.”

This article originally appeared on Time.com.