Lonely people are more likely to suffer high blood pressure than others, according to a study published by University of Chicago researchers Louise Hawkley and John Cacioppo.

“Quite a few studies have shown social support as a moderator and predictor of physiological measures of health,” Hawkley said. “The size of the effect was pretty phenomenal. It was on par with the kinds of things we see with smoking and obesity.”

As far back as the late 1980s, researchers found significantly higher mortality rates among people who were objectively isolated—those who had few connections with family or friends, who rarely went to church, and who had little or no social network.

Results like these prompted researchers to ask broader questions about the relationship between socialization and health.

“We realized that it wasn’t necessarily just objective isolation that was important,” Hawkley said. “People’s perception of their social situation might have an effect.”

Researchers linked loneliness to health, which was measured as the disparity between what a person wants from their social environment and what they are actually getting.

Hawkley and Cacioppo studied 229 people between the ages of 50 and 68, selected randomly from a larger study on aging. The subjects were asked for reactions to statements revealing satisfaction with their social life, such as “I have a lot in common with the people around me” and “I can find companionship when I want it.” Based on their responses, researchers categorized subjects as lonely or non-lonely. Loneliness was associated with a 30-point rise in systolic blood pressure.

Hawkley emphasized that the study simply shows association. “We can’t make a causal statement…yet,” she said.

Hawkley said stricter evidence of a causal relationship might not come for several years.

“If something is going on making patients lonelier, we can watch to see if and how blood pressure changes as well.”