From where in the body might kindness flow? Folklore and belief systems far and wide point to the heart. Ancient Egyptian mythology, for example, maintained that the leap to the afterlife required a test. Before the deceased could enter, their heart had to be weighed, placed on a balance under the watchful eyes of the gods.
The dead person’s heart wasn’t beating, but it wasn’t considered dead weight; it held proof of virtue. If the person had lived a life of goodness, their heart would be light as a feather — and the gates to the afterlife would swing open. But if their life had been filled with greed, their heart would be heavy. For this person, there would be no welcome to the afterlife; instead, their heart was fed to Ammit, a soul-devouring goddess with the forequarters of a lion, the hindquarters of a hippo, and the head of a crocodile.
This ancient tale is just one example of the heart’s symbolic link to goodness. Christian art depicts Jesus’s heart aglow, sacred and filled with benevolence. Hindu and Buddhist traditions consider the heart chakra the center of compassion.
And in Dr. Seuss’s tale, the Grinch’s heart is two sizes too small.
With advances in our understanding of anatomy and physiology over the past few centuries, science has shifted the focus for our actions and emotions from the heart to the brain. Yet, in a sense, the ancient Egyptians may have been on to something. Emerging evidence suggests that good deeds can become etched into our bodies, including the cardiovascular system — and that our hearts and our health benefit when we are kind to others.
The chemistry of kindness
In his book The Healing Power of Doing Good, nonprofit leader Allan Luks quoted survey respondents attempting to articulate the feelings they experienced when doing volunteer work. “It makes you explode with energy,” one said. Others described “a relaxation of muscles that I didn’t even realize had been tensed” and a “euphoric” feeling of being “zapped by an energy bolt.” Luks coined the term “helper’s high” to describe these feelings.
Dopamine is released when we give to others. Scientists have actually witnessed this in the lab.
This sensation has physiological origins. Gregory Fricchione, the Mind/Body Medical Institute Professor of Psychiatry at HMS and director of the Benson-Henry Institute for Mind Body Medicine at Massachusetts General Hospital, describes it as a release of “chemical juice.” When we help others, he says, neurotransmitters flow up in a tight bundle of axons called the medial forebrain bundle through the subcortex with “exit ramps to many of the important structures of the brain” — the fear-conditioning amygdala, the memory-forming hippocampus, and the motivation-moderating medial prefrontal cortex.
Among these neurotransmitters is dopamine. This feel-good chemical is linked to the brain’s reward center. And it’s released when we give to others. Scientists have actually witnessed this in the lab. A few years ago, a small study from an international research collaboration that included scientists from the National Institutes of Health used magnetic resonance imaging to measure brain activity associated with making a charitable donation. The findings, reported in PNAS, suggested that this action engages the mesolimbic system of the brain, triggering a euphoric rush of dopamine in much the same way that anticipating a reward, like money, does.
Numerous other processes may be implicated in the helper’s high, says Fricchione: pain-reducing endogenous opioids, endorphins, and perhaps even the neuromodulating chemicals that make up the endocannabinoid system. Then there’s oxytocin, the so-called affiliation hormone, which has plentiful receptors in the amygdala, where it helps suppress fear and anxiety.
Best known for its role in inducing contractions during childbirth and in mother-infant bonding, oxytocin is closely linked to empathy and altruistic behavior.
Oxytocin receptors are found throughout the cardiovascular system, including in the heart. The hormone can cause blood vessels to widen, encouraging blood flow and lowering blood pressure. And it’s been shown to counteract oxidative stress and inflammation, both of which can contribute to atherosclerosis, heart attack, and stroke — a hint of how the transient mood boost one gets from helping others may relate to longer-term health.
Survival of the selfish?
The molecules rewarding good deeds with good feelings are linked to ancient, deep-rooted instincts. Perhaps their release is an evolutionary nod that whatever we are doing — including giving — is good for us. But this possibility raises a paradox that has irked evolutionary theorists dating back to Darwin: If the natural world has been shaped by cutthroat competition, what explains our drive to share limited resources with others?
When Stephen Post was a high school student in the late 1960s, there was a focus on the brutishness of human nature. Trendy books like Lord of the Flies and The Territorial Imperative emphasized people’s more selfish and violent tendencies. “There was a bias toward cynicism that I feel was unfounded,” recalls Post, who, in addition to directing the Center for Medical Humanities, Compassionate Care, and Bioethics at Stony Brook University, heads the board of directors for the Institute for Research on Unlimited Love, a nonprofit that disseminates research on the health benefits of kind giving. “To be kind was to be deluded. The thinking was, as the French philosopher Sartre argued, if anybody looks at you with kindness, watch out, because they’re after your wallet. But you really can’t explain an awful lot of human behavior with that model in mind.”
Since then, Post says, science has helped “rewrite the story” by highlighting the ubiquity of altruism across cultures throughout human history. For example, researchers have identified an intrinsic propensity in toddlers as young as fourteen months to help others with tasks without being influenced by rewards, encouragement, or threats.
Fricchione sees altruistic pro-social behavior as a logical extension of fundamental mammalian behaviors — the drive to nurture offspring and attach to caregivers. “It would be strange if evolution only provided us with a brain reward-motivation circuitry that supported ‘gimme, gimme,’” he says. “Of course, we know individuals like that, and they make us angry and frustrated, because we feel they aren’t behaving as good mammals. Evolution has provided us with the structures and functions that remind us that we survive better by cooperating as a group — not only when we’re seeking social support, but when we’re giving it.”
Post agrees that the key is in community. “Group selection theory says that a certain amount of our evolution occurred in groups,” he says. “So, my group is going to do better to the degree that it exhibits compassion and helping behavior.”
In 2010, Nicholas Christakis, MD ’89, a sociologist-physician who then held faculty positions at HMS and Harvard University, attempted to map out how groups could become kind. Analyzing data from a series of experiments that used a “public goods game,” in which participants could dole out money, in the form of tokens, to strangers who were also participants in the experiments, he found that those who received funds from others were more likely to give money to other strangers in a future game. An individual’s generosity caused a chain reaction that reverberated out, extending to three degrees of separation. Capturing the pay-it-forward phenomenon in the lab, these findings, published in PNAS, drew widespread interest.
“How two people treat each other in one part of the city may relate to how two other people treat each other in another part of the city,” says Christakis, who now directs the Human Nature Lab at Yale University. In other words, he says, “altruism is contagious.” The kindness of individuals cascades, ultimately creating a stronger group that is better equipped to survive.
Christakis sees kindness as one of several pro-social tendencies we’ve evolved because they are key to maintaining social cohesion, a thesis he describes at length in his 2019 book, Blueprint: The Evolutionary Origins of a Good Society. The flip side of this, he adds, is that we find it stressful to be antagonistic or to be alone. Isolation from a group “causes wear and tear on our body,” explains Christakis. Indeed, according to the American Heart Association, loneliness and social isolation are associated with a 29 percent increased risk for heart attack or premature death, while emotions like anger and hostility are also considered to be coronary disease risk factors.
To Christakis, those health threats are “the kind of inverse of evolution’s way of telling us to be kind. We have to be kind to other people so they’ll want to be in our group, and we have to support the group so that the whole is greater than its parts.”
While the health benefits of kindness are probably not incidental, Christakis adds, they are multifaceted. It’s not as straightforward as saying that kindness can completely prevent or cure a disease. “Pro-social behaviors like kindness are probably exceedingly complex physiologically, acting upon our bodies in multiple ways, not all of which are understood.”
Sense of purpose
How does this complex mix play out in the modern world? One way to find out is to examine the health outcomes of people who complete measurable acts of altruism. In a 2013 randomized controlled trial published in JAMA Pediatrics, a group of teens was assigned to complete volunteer work. After two months of weekly volunteering, the young people displayed significant decreases in risk factors for cardiovascular disease — systemic inflammation, total cholesterol levels, and BMI — compared to their non-volunteering peers.
Other research has found lower risk of early death among those who volunteer. A 2020 American Journal of Preventive Medicine study of nearly thirteen thousand volunteers over age 50 who were assessed over a four-year period revealed that those who spent more than a hundred hours per year volunteering had a 44 percent lower risk of mortality compared to those who did not volunteer, even after controlling for factors like stress, health behaviors, and personality traits.
One of the authors of that study is Eric Kim, an affiliate scientist at the Lee Kum Sheung Center for Health and Happiness at the Harvard T. H. Chan School of Public Health. Kim acknowledges that the physiological mechanisms linked to the helper’s high could drive health benefits, but he also highlights additional drivers. Volunteers tend to get more exercise, use preventive health services more often, and experience better social cohesion, for example.
Kim, who is also an assistant professor of psychology at the University of British Columbia, argues that one of the most important effects of volunteering is that it contributes to a person’s sense of purpose. “If you have a will to live, that will to live will help push you past all kinds of barriers that emerge when you’re trying to enact positive health behaviors,” he says.
In a study of nearly fourteen thousand retired adults published in 2020 in Preventive Medicine, Kim and colleagues found that those with a higher sense of purpose in life had a lower likelihood of becoming physically inactive, having sleep problems, or developing an unhealthy BMI. Similarly, a 2016 meta-analysis in Psychosomatic Medicine described a lower relative risk for cardiovascular events among people with a higher sense of purpose, even after controlling for variables like conventional cardiovascular risk factors and psychological distress.
“People often ask me how they might increase their sense of purpose,” says Kim. “The answer is, it’s very difficult. But one of the most scalable ways, that is kind of on the easier side, is volunteering.”
Giving from the heart
Yet even if it’s relatively easy to get into volunteering, it’s not just about going through the motions. Kim points to a 2012 study in Health Psychology that found a lower risk for premature mortality among volunteers — but there was a caveat. Surveying participants about their motivations, researchers found that those who volunteered for self-oriented reasons had a similar mortality risk as those who didn’t volunteer at all. And in the JAMA Pediatrics paper on teen volunteers, the cardiovascular benefits of volunteering were greater among those individuals whose survey responses displayed an uptick in empathy, defined as caring about what happens to other people.
Acts of altruism can also burden the body. Caregiving, for example, can become an immense stressor contributing to myriad health issues. That’s why Post doesn’t think that altruism itself is the best medicine. “Altruism really conveys an action; it can be habitual, routinized, or externalized,” he says. “It doesn’t get to the kindness. It doesn’t get to the heart.” Rather, intentional acts of kindness that do not become a burden are key. Post describes what he calls “kind giving” or “kind altruism,” an idea related to the Buddhist concept of loving-kindness that meditation works to finesse. “It’s not how much you do for others, but the kindness you pour into it,” he adds.
Researchers found that those who volunteered for self-oriented reasons had a similar mortality risk to those who didn’t volunteer at all.
Christakis points out that a propensity for kindness, like any evolved tendency, varies between individuals. But there are ways to cultivate it. He remembers a radio interview he listened to during a drive from Cambridge to the Longwood campus thirty-five years ago. The interviewee, a Buddhist monk, was asked how he might maintain his state of Zen instead of succumbing to road rage if a driver cut him off on the streets of Boston.
“I recall that, without missing a beat, the monk said he would imagine that in that car, there’s a woman in the back, and the man is driving desperately because she’s pregnant and going into labor,” says Christakis. “So, the monk had trained himself to reframe what was happening around him in the most positive and favorable light.”
Post echoes the importance of cultivating a kind disposition that pervades one’s life — whether you’re donating money, volunteering, or just stuck in a traffic jam. “The science bears this out. It’s how you can actually de-stress. It’s how you can be visionary. And it’s how you can experience joy and happiness,” he says.
“It’s actually pretty simple,” Post adds with a shrug. “I mean, you can just be kind.”
Molly McDonough is the associate editor of Harvard Medicine magazine.
Images: The Trustees of the British Museum (papyrus); John Soares (Fricchione); Evan Mann (Christakis)