Growing up on Long Island, New York, young Stephen Post often received an unusual prescription from his mother when he was feeling grouchy or under the weather. “She’d say, ‘Why don’t you go out and help someone?’” he recalls. “I’d go out and help Mr. Muller rake leaves or help old Bobby Lawrence fix his boat. Then, I’d come back feeling better, and feeling better about life.”

Decades later, Post—a professor of preventive medicine at New York’s Stony Brook University—is among a growing contingent of researchers exploring just how such acts of generosity and the feelings (empathy, compassion, altruism) that prompt them may actually improve our mental and physical health.

Recent studies have shown that people that volunteer live longer, suffer less chronic pain, have bolstered immune systems, are more likely to recover from addiction, and experience an in-the-moment sense of calm akin to that which people experience during and after exercise. Scientists have yet to fully understand what the physiological underpinnings are of such health benefits, but early studies credit a cascade of neurobiological changes that occur as we reach out to help a loved one, or (in some cases) even cut a check to a stranger in need.

Could generosity be the missing, often overlooked ingredient to a prescription for better health? Perhaps, says Post, author of The Hidden Gifts of Helping: How the Power of Giving, Compassion and Hope Can Get Us Through Hard Times. “This is a young science, but what we have begun to discover is that there is something going on, physiologically, in this process of helping others that seems to make people feel happier and report greater health.”

Helping Hands Live Longer

We’ve all felt it: That blush of inner-warmth we get after we bring a plate of healthful, steaming food to a sick relative, volunteer to read to kids at a local preschool or help sort donations for a shelter.

According to a 2010 survey of 4,500 Americans by United Healthcare, 68 percent of those that volunteered in the previous year reported that doing it made them feel physically healthier; 73 percent noted that it lowered their stress levels. Meanwhile, 29 percent of volunteers that suffered from a chronic illness claimed that giving of their time helped them to better manage the illness.

Other studies, by researchers at Boston College, found that when chronic pain sufferers volunteered to help others with similar conditions, they saw their own pain and depression levels decrease. At least seven studies have shown that people that regularly volunteer or give of themselves live longer—especially if they do it for genuinely altruistic reasons.

Cami Walker, 38, of Denver, has experienced firsthand the physical benefits of being generous. After one sleepless night, lying awake and, “feeling sorry for myself,” due to a flare-up of her multiple sclerosis, she decided to take the advice of a spiritual teacher that suggested she, “Give something away each day for 29 days.”

On day one, she called a sick friend to offer her support. On day two, she dropped $5 in a hat for some street performers. Another day, she treated a friend to a foot massage. By day 14, she recalls, “My body was stronger and I was able to stop walking with my cane. After months of being too sick to work, I was able to go back part-time.”

Walker subsequently wrote the bestselling 29 Gifts: How a Month of Giving Can Change Your Life. It has inspired a global giving movement, with participants blogging about their experiences at 29Gifts.org. As she recently explained to The New York Times, “It’s about stepping outside of your own story long enough to make a connection with someone else.”

The Helper’s High

University of Michigan researcher Sara Konrath, Ph.D., has found that people engaging in acts that benefit others tend to have more calming hormones like oxytocin and progesterone coursing through their bodies. If presented with a tough situation later, they are likely to react with a muted stress response, churning out fewer harmful stress hormones, such as cortisol and norepinephrine, and maintaining a calmer heart rate. Konrath is studying whether altruistic thoughts and behavior might also be associated with an anti-inflammatory effect on the body.

“Just thinking about giving seems to have a beneficial physiological impact,” says Post. For instance, a late 20th-century study by then Harvard Psychologist David McClelland found that when people watched a film about Mother Teresa’s work with orphans in Calcutta, levels of immunoglobulin A (a marker of immune strength) shot up. A more recent study found that people had higher levels of oxytocin in their blood after they had watched a moving film about an ill 4-year-old boy.

Some research further suggests that the act of giving may release natural opiates, such as endorphins, into our system. One landmark analysis of 1,700 people published in Psychology Today found that more than 68 percent experienced a “helper’s high” when physically helping another person, and 13 percent reported a decrease in aches and pains afterward. It’s a concept that’s been documented many times since.

Meanwhile, new brain-imaging research has shown that acts of giving (including making a charitable donation) stimulate “reward centers” in the brain. This includes the mesolimbic pathway by which natural dopamine is released, leaving us feeling euphoric.

On the flip side, “We found that people that are high in narcissism and low in empathy have higher cortisol levels,” advises Konrath. “They walk around with high stress reactivity, which is really hard on the body.”

One other clear example of the health benefits of helping lies in the field of addiction research. Recent studies by Maria Pagano, Ph.D., an associate professor of psychology at Case Western Reserve University School of Medicine, found that recovering addicts that volunteer to help other addicts stay sober are twice as likely to remain so themselves. That’s because narcissism and self-absorption are often at the root of addiction, and generosity is an antidote to narcissism, Pagano says.

“The founders of AA (Alcoholics Anonymous) figured it out,” Pagano continues, noting that a primary focus is on serving others. “They figured out that this selfish root is there before the illness develops, and is sustained unless you treat it. This is treatment; it is a way of continually weeding out the narcissism that made you sick.”

Born to Give

Stephanie Brown, Ph.D., an associate professor of preventive medicine at Stony Brook, is the daughter of an evolutionary psychologist and a pioneer in the study of altruism’s neurobiological roots. In sharp contrast to what she describes  as the long-held “self-interested” assumption about human nature (that we help others only to help ourselves), she suggests that humans are biologically wired to be empathetic and generous.

“It makes more sense from an evolutionary perspective for us to suppress self-interest,” for the benefit of the whole sometimes, she says. New research from the University of Washington suggests that babies as young as 15 months old exhibit fairness and empathy.

So, why don’t we always stop to help? Our anxious, busy, modern-day lives get in the way, suggests Brown. “It could be that our natural, default state is to help when we see need, but what prevents that is our stress response.”

That is, stress often gets in the way: Maybe we pass a stranded motorist on the road, but drive on by because we’re on a timetable. Perhaps our instinct is to offer a helping hand to a homeless person, but we fear that more will be asked of us than we are prepared to give. We wish to bring a meal to a dying relative, but are apprehensive about what to say when we visit.

Brown’s recent federally funded studies show that at least some of the calming hormones and quietness of heart often seen in habitual givers may actually precede and enable their acts of selflessness by interrupting their potential stress response before it stalls their helping hand. “I am suggesting that when you see helping going on, something beneficial has already happened to the giver’s body,” says Brown.

When givers perceive a need, instead of fretting and fleeing, they calmly stop to help. In the end, everyone walks away feeling a little more generous.

Lisa Marshall is a freelance health writer in Boulder, CO. Connect at LisaAnnMarshall.com.