Marcia Trenholm doesn't need a scientific study to understand why volunteering is good for her.
Two days a week, the retired insurance company auditor gives her time to the University of Massachusetts Boston Pension Action Center, helping clients track down lost benefits. Other times, she can be found at a local senior center, serving as a certified guide for people who are new to Medicare.
Volunteering, she said, leaves her feeling engaged and energized. It connects her with other people and gives her a sense of purpose.
"I get a lot out of it actually," said Trenholm, 68, of Belmont. "I'm able to give, but I'm also able to get."
An increasing amount of research on the mental and physical health benefits of volunteering says she's exactly right.
For decades, researchers have seen a link between better health and volunteering, said Jeffrey Burr, a professor of gerontology at UMass Boston. Evidence, including from several studies Burr led or co-wrote, has grown exponentially.
"We're convinced that volunteering does have positive ramifications for well-being," Burr said.
Researchers can't explain all the connections yet. But some are clearer than others, such as the link to mental health.
"Compared to non-volunteers, volunteers have less depression, less anxiety, higher self-esteem, higher life satisfaction, greater happiness and greater sense of meaning in life," Burr said.
Burr also has examined how volunteering affects heart health. In a study published in The Gerontologist in 2015, middle-aged volunteers were less likely to have abdominal fat and high blood glucose than non-volunteers. They also had healthier levels of "good" HDL cholesterol. Older volunteers were less likely to have high blood pressure than their non-volunteer counterparts.
Other studies have had similar findings. One, published in JAMA Pediatrics in 2013, found that high school students who were asked to volunteer had better markers for heart disease risk than high schoolers who were told to wait for a semester.
Eric Kim, an assistant professor of psychology at the University of British Columbia in Vancouver, Canada, co-wrote a study that looked at relationships between volunteering and health in nearly 13,000 U.S. adults over 50. Echoing earlier work, this study, published in 2020 in the American Journal of Preventive Medicine, found that people who volunteered at least 100 hours per year had a reduced risk of dying over a four-year follow-up period compared with non-volunteers.
Kim's work, however, did not link volunteering with benefits to specific health conditions such as high blood pressure. Such contrasts with other research highlight why experts are still working to answer the question of why, exactly, volunteering is healthy.
"That's really sort of the cutting edge right now," Burr said.
Part of it may be stress reduction. Chronic stress is a risk factor for poor health, and volunteering seems to alleviate its harm.
Research has linked volunteering with increased physical activity and reduced loneliness, Kim said. "Loneliness actually has a pretty large negative impact on physical health," he said.
Volunteering can help build stronger social networks in a way that probably differs from simply hanging out with friends, Kim said. Volunteering, he said, has an "overarching, outward-focused, pro-social motivation," making it more "soul-nourishing."
There might be an evolutionary basis for that, Kim said. Some scientists theorize that early humans would have benefited from helping one another, which means we might be hard-wired to feel rewarded by generous activity. Kim noted a 2011 study in Health Psychology that suggested people who volunteered for altruistic reasons were at lower risk of dying four years later than non-volunteers, while those volunteering for self-centered purposes saw no benefit.
It's unclear how specific volunteer work might affect people, Kim said. "That is another important factor that has just not been examined particularly well."
But it's easy to envision possible connections, he said. For example, a volunteer in a health care setting might learn more about health resources, which might lead them to make more preventive care visits.
Burr speculated that volunteers who do work such as Trenholm's at the pension center – which she likened to "a detective job" – would be mentally stimulated, which might help explain benefits to cognitive health. A volunteer who packs crates at a food pantry would get more exercise.
Several studies, including Kim's, have found that about two hours a week seems to be the minimum for seeing a health benefit.
According to a survey released earlier this year by AmeriCorps and the U.S. Census Bureau, more than 60.7 million people formally volunteered with organizations between September 2020 and 2021. Opportunities abound for joining their ranks, Burr said. "There's a lot more demand than supply."
Kim said a good place to start is by typing the words "core values list" into a search engine. That will provide a list of adjectives such as "kindness," "integrity" or "spirituality." Zero in on a value that matters to you, he said, then find an organization that embodies it.
Kim volunteers his own skills to help nonprofits with statistical analysis. "It reminds me of why I do things," he said. "Academia can be quite difficult a lot of the time, and it really grounds me."
He said it also honors the spirit of his grandfather, who ran an orphanage in South Korea. (Burr notes that some researchers have suggested interest in volunteering is passed down intergenerationally.)
Trenholm said she spends about 17 hours a week on her two volunteer jobs. With each, "I'm always learning something new." At the senior center, she enjoys getting to meet people face-to-face. The pension research, which she does from home, "keeps me stimulated and active," she said.
And the fact that she gets that while helping others overcome sometimes significant problems makes it even more rewarding, she said. "I feel very grateful that I can make such a difference in somebody's life."