The idea that social media can be harmful to our mental and emotional well-being is not a new one, but little has been done by researchers to directly measure the effect; surveys and correlative studies are at best suggestive. A new experimental study out of Penn State, however, directly links more social media use to worse emotional states, and less use to better.

To be clear on the terminology here, a simple survey might ask people to self-report that using Instagram makes them feel bad. A correlative study would, for example, find that people who report more social media use are more likely to also experience depression. An experimental study compares the results from an experimental group with their behavior systematically modified, and a control group that’s allowed to do whatever they want.

This study, led by Melissa Hunt at Penn State’s psychology department, is the latter — which despite intense interest in this field and phenomenon is quite rare. The researchers only identified two other experimental studies, both of which only addressed Facebook use.

One hundred and forty-three students from the school were monitored for three weeks after being assigned to either limit their social media use to about 10 minutes per app (Facebook, Snapchat and Instagram) per day or continue using it as they normally would. They were monitored for a baseline before the experimental period and assessed weekly on a variety of standard tests for depression, social support and so on. Social media usage was monitored via the iOS battery use screen, which shows app use.

The results are clear. As the paper, published in the latest Journal of Social and Clinical Psychology, puts it:

The limited use group showed significant reductions in loneliness and depression over three weeks compared to the control group. Both groups showed significant decreases in anxiety and fear of missing out over baseline, suggesting a benefit of increased self-monitoring. Our findings strongly suggest that limiting social media use to approximately 30 minutes per day may lead to significant improvement in well-being.

It’s not the final word in this, however. Some scores did not see improvement, such as self-esteem and social support. And later follow-ups to see if feelings reverted or habit changes were less than temporary were limited because most of the subjects couldn’t be compelled to return. (Psychology, often summarized as “the study of undergraduates,” relies on student volunteers who have no reason to take part except for course credit, and once that’s given, they’re out.)

That said, it’s a straightforward causal link between limiting social media use and improving some aspects of emotional and social health. The exact nature of the link, however, is something at which Hunt could only speculate:

Some of the existing literature on social media suggests there’s an enormous amount of social comparison that happens. When you look at other people’s lives, particularly on Instagram, it’s easy to conclude that everyone else’s life is cooler or better than yours. When you’re not busy getting sucked into clickbait social media, you’re actually spending more time on things that are more likely to make you feel better about your life.

The researchers acknowledge the limited nature of their study and suggest numerous directions for colleagues in the field to take it from here. A more diverse population, for instance, or including more social media platforms. Longer experimental times and comprehensive follow-ups well after the experiment would help, as well.

The 30-minute limit was chosen as a conveniently measurable one, but the team does not intend to say that it is by any means the “correct” amount. Perhaps half or twice as much time would yield similar or even better results, they suggest: “It may be that there is an optimal level of use (similar to a dose response curve) that could be determined.”

Until then, we can use common sense, Hunt suggested: “In general, I would say, put your phone down and be with the people in your life.”