"... more than 20 percent of the adult population in America admits to struggling with loneliness. That's more people than have diabetes in our country. That's more than adults that smoke ...."

Former U.S. Surgeon General Vivek Murthy

As everyone knows, the best way to stay healthy and live to a ripe old age is to pick your parents well — it's all about good genes. After that, you're on the right track if you don't smoke, avoid alcoholism and obesity, skip red meat and take your Omega-3s. Everyone knows ... and everyone's wrong. The very best thing you can do for your health is to have happy relationships while avoiding social isolation and loneliness.

That's what a raft of studies concludes, some of which have been tracking literally millions of people from every walk of life for decades. Take the ongoing Harvard Study of Adult Development, begun in 1938, whose original participants included John F. Kennedy and longtime Washington Post editor Ben Bradlee. The study showed, for instance, that the role of genetics and long-lived ancestors was less important to longevity than one's level of satisfaction with relationships in midlife.

In 2015, fourth and current director of the study, Professor Robert Waldinger of the Harvard Medical School, gave a TED talk, "What Makes a Good Life? Lessons from the Longest Study on Happiness," that's been viewed more than 13 million times. "The people who were the most satisfied in their relationships at age 50 were the healthiest at age 80," he said. "When we gathered together everything we knew about them about at age 50, it wasn't their middle-age cholesterol levels that predicted how they were going to grow old." Waldinger's bottom line: "Loneliness kills. It's as powerful as smoking or alcoholism."

Another study, a meta-analysis published in 2015 by Brigham Young University researchers, confirmed the Harvard study. After examining the health records of over three million participants going back to 1980, they wrote, "Across studies that statistically controlled for a variety of possible confounds, the ... average effect sizes for social isolation ... loneliness ... and living alone [corresponded] to an average of 29percent, 26 percent and 32 percent increased likelihood of mortality, respectively."

It's not hard to see why isolation and loneliness have such a powerful effect on health. We're innately social creatures. Our hunter-gatherer ancestors lived in tribes and if you were separated from your tribe back then, you were at risk of starving or being eaten by a predator. Today, our Stone Age genes respond to loneliness and isolation by causing our bodies to enter a chronic stress state, causing inflammation that leads to high blood pressure, susceptibility to infection and poor immune functioning. Think heart attacks strokes, and vulnerability to viruses such as influenza and COVID-19.

Of course, we're don't all react the same. Some of us may be surrounded by many people but still feel alone, while others may simply isolate themselves, preferring their own company to that of other people. Oddly, though, the BYU study found the negative effect on longevity is about the same for those two scenarios.

One third of people older than 65 live alone and the situation isn't getting any better. As study co-author Tim Smith explained, "Not only are we at the highest recorded rate of living alone across the entire century, but we're at the highest recorded rates ever on the planet. With loneliness on the rise, we are predicting a possible loneliness epidemic in the future."