A renowned Harvard University doctor reveals why being happy is an even better predictor of a long life than your cholesterol levels are. Plus, his most shocking scientific discovery about how to become happy—all based on 100 years of Harvard health data.
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Highlights
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Happy people don’t just feel better—they live longer, and they’re more likely to enjoy good health during those extra years. This was one of the biggest findings of the ongoing Harvard Adult Development Study, the longest-running study of adult health and happiness in the world.
The study began in 1938, with researchers following 724 men throughout their lives. It’s since expanded to more than 2,500 participants, including the children of the original group. Over the decades, researchers collected an extraordinary amount of data from medical records, in-person interviews, and questionnaires. What they’ve learned so far is detailed in The Good Life, co-authored by the current director of the study, Robert Waldinger, MD, and its assistant director, Marc Schulz, PhD.
Dr. Waldinger, who is also a psychiatrist at Massachusetts General Hospital and a professor of psychiatry at Harvard Medical School, chatted with The Healthy about the project’s results—including what really makes people happy and why it’s the most important thing you can do for your health.
He also shares the study finding that surprised him the most. (Hint: it has nothing to do with whether or not you’re ticklish—one of the stranger questions that’s been on the study questionnaire for nearly 100 years. “I still have no idea why they put it on there originally, but we’ve kept it just in case!”)
About the expert
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Before you can figure out what makes you happier, and therefore healthier, you first need to understand that many of us have been misled about the true sources of happiness, Dr. Waldinger says.
Despite the wide range of gadgets, products, entertainment, and self-help seminars touting to make you happy, the truth is that our current social structure isn’t designed with individual happiness in mind. In fact, many of our modern institutions and conveniences are quietly making us desperately unhappy.
“Life today is a haze of competing social, political, and cultural priorities, some of which have very little to do with improving people’s lives,” he says. “The modern world prioritizes many things ahead of the health and happiness of human beings.”
In a July 2025 video shared by Harvard T.H. Chan School of Public Health, Dr. Waldinger describes two “flavors” of happiness.
Hedonic well-being is the moment-to-moment feeling of pleasure, the fun, enjoyable, feel-good experiences. It’s real and valuable, but it’s often fleeting, even from one hour to the next.
Eudaimonic well-being, on the other hand, represents a deeper, long-term sense of contentment. “Even when I’m having a bad day, life is basically good,” he explains. This stable form of happiness is what’s most strongly tied to health and longevity.
Think you’ll know your happiness when you find it? When people were surveyed about what they thought would make them happy, the most common response was getting rich, followed by becoming famous, having a successful career, traveling a lot, and having an “easy” life.
In reality, none of these reliably bring happiness on their own.
This truth is shown through the lives of two study participants featured in The Good Life, John and Leo. John was a wealthy, well-known, Harvard-educated lawyer from a prominent family. Leo was a high-school art teacher from a bad neighborhood, just eking out a living. Yet John was the unhappiest man recorded in the history of the study, dying after decades of health problems. In stark contrast, Leo was identified as the happiest, staying active and healthy well into old age.
Clearly, money can’t buy health or happiness—but why, exactly? The answer surprised even Dr. Waldinger.
“In analyzing all that data, the thing that surprised me the most was finding that our relationships are the most important factor in happiness, and that how happy we are in our relationships has a powerful influence on our health,” he says. “The size of the effect was huge! The people who were the most satisfied in their relationships at age 50 were the healthiest at age 80.”
The study found that people with a range of close relationships—whether with romantic partners, family, friends, or even coworkers—were happier and healthier over time. But it wasn’t the types nor the number of relationships a person had that mattered most. It was the quality of those connections, Dr. Waldinger says.
“We found that human beings need exercise, nutrition, and a sense of purpose—but most of all, we need each other,” he says. “Taking care of your body is important, but tending to your relationships is a form of self-care too. That’s the revelation.”
According to the Harvard Adult Development Study, the single best thing you can do for your long-term health is to find, nurture, and preserve close relationships.
One of the most striking correlations the researchers discovered: people’s reported satisfaction with their relationships at age 50 was a better predictor of their physical health than their cholesterol levels. In fact, having close relationships was a stronger predictor of overall health than IQ, social class, wealth, or even genetics.
Here are just a few of the health benefits of high-quality relationships that the researchers found:
The key, Dr. Waldinger explains, is that good relationships help manage stress in a powerful way—and when your stress hormones are better regulated, inflammation in your body lowers. Because chronic inflammation contributes to a wide range of health problems, these findings suggest that strong relationships may play a meaningful role in protecting your long-term health.
Most of the book focuses on relationships—so we asked Dr. Waldinger to share the health habits he personally practices. Here’s what he revealed:
“When people hear about our research, so many people ask, ‘Is it too late for me to be happy?’ and the answer is a resounding ‘No!’,” he says. “We found that about 40% of your happiness is under your direct control. It’s never too late to choose happiness.”
Choosing is the key word here. Simply waiting for things to change in a way that makes you happy is a highway to heartbreak. Happiness isn’t about what happens to you, but how you respond to it. “The good life is forged from precisely the things that make it hard,” he concludes.
And a major part of how you deal with those hard things is through building relationships. “Living in the midst of warm relationships is protective of both mind and body.”
So if you do just one thing for your health today, he recommends the final item on his personal list: think of someone, anyone, and reach out. In person is ideal, but a phone call or even a text message counts.
In other words: science says call your mom.
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