Loneliness has been linked to poor health, but it’s been unclear why. Lianne Kurina of the University of Chicago and her team tested the theory that poorer sleep might be what predisposes lonely people to high blood pressure, heart disease and even earlier death.

The researchers examined 95 people from a close-knit religious community in South Dakota centered around farming. The subjects did interviews, and then wore a special sensor called a wrist actigraph for a week to measure their sleep.

“Our study population in general was not very lonely” says Kurina, an assistant professor of health studies at the University of Chicago. “So it was surprising to find that even subtle differences seemed to translate into differences in sleep patterns.”

Specifically, the lonelier subjects slept just as long, but tossed and turned more and had more frequent wakings. The subjects did not seem aware of the difference in sleep quality, as there was no difference in the subjective reports people gave of their sleep.

The results match up with an earlier study of college students, a much more diverse group with widely varying senses of loneliness. Kurina says the consistency of results across these two very different groups suggests it might be a wide-reaching effect. The authors of the study, which appears in the journal Sleep, speculate it might have to do with a basic need to feel connected and secure in order to sleep soundly.