“There are, however, many possible explanations,” said Ben Lennox Kail, a sociology and gerontology researcher at Georgia State University in Atlanta who wasn’t involved in the study.

For starters, people with few close relationships with friends or relatives may be more likely to suffer from depression or other mental health issues than individuals with expansive social networks, Kail said by email.

“People who are not particularly well socially integrated may have poorer mental health or well-being, which may lead to poorer physical health, which may make longer hospital stays and more repeat visits more necessary,” Kail said.

“That said, if this were the primary explanation, we might expect to see more regular doctor’s visit—and we don’t,” Kail added.

“Instead, it’s possible that people without friends and family to rely on might benefit more from longer hospital stays where they can get extra support from nurses,” Kail said. With strong social networks, people might also have healthier habits, more reasons to leave the house and keep active, and people in their life to remind them to eat right, exercise, and take any prescribed medicine.

For the study, Nicole Valtorta of Newcastle University in the UK and colleagues examined data from 126 studies involving a total of more than 226,000 people in 19 countries. Most were from the United States and Canada.

Only one study was a controlled experiment designed to test whether social relationships directly impacted health utilization. Most of the studies examined data collected over time on outcomes like emergency room visits, doctor checkups, and hospital admissions.

Valtorta declined to comment on the study, citing an ongoing strike over pensions at the university.

“The evidence is not quite there yet to indicate that increasing the quantity and/or quality of older adults’ social ties will reduce health care utilization,” said Christina Matz-Costa of the Boston College School of Social Work.

“That is not to say that individual or population-based interventions to strengthen social relationships and reduce loneliness do not represent important public health strategies,” Matz-Costa, who wasn’t involved in the study, said by email.

“When health issues arise, informal networks are often used to obtain advice, guidance, and support,” she said.

That help can allow them to understand their symptoms before seeking out formal care services.