According to the longest and most extensive longitudinal study of human development, looking at 85 years of data at this point, scientists have concluded the true X factor in avoiding a myriad of negative health outcomes, as well as the key driver of happiness.

Is it diet/obesity risk? No.

Is it getting enough exercise? No.

Is it smoking? No.

Is it wealth/class/professional success? No.

Is it race? No.

Is it gender? No.

These are all very important factors in long-term health. But not the most important factor, according to the Harvard Study of Adult Development.

Put simply, the most important thing you can do to live longer and be happier? Make a friend.

RELATED: How To Make Friends As An Adult, According To 22 Experts

The steady decline in social connections

For a while now I have been on a soap box about male mortality being six years shorter than women because of the health risks associated with loneliness and isolation (See Jed Diamond, who is the expert on this topic, speak here). Men have massively higher rates of suicide, booze and drug deaths, and many others.

Last night I was talking to my old friend Andrea Miller, the founder and CEO of YourTango (yes, the website you're reading right now). She calls her site a "purpose-driven publisher focused on love, relationships, emotional wellness, and self-empowerment". Right underneath that tagline is supporting readers in their search for meaning and connection.

Then, this morning I was scrolling through my most recent podcast episodes as I headed out for my morning run. I hit a head-scratcher. Five Thirty Eight, the political data analytics team founded by Nate Silver, had an episode with a Zen priest on loneliness. I rarely listen to anything political, as I find our extremist world too upsetting. But I had to check this out.

In 51 minutes, Robert Waldinger wove together many of the strands of my current thinking. Waldinger is the Zen priest, Harvard psychiatrist and director of the Harvard Study of Adult Development currently housed at MGH. 

Waldinger talks about the steady decline in social connections starting in 1950. By 2021, more than one-third of Americans report experiencing "serious loneliness."

RELATED: 19 New Things To Try When You'd Rather Stay In Bed Than Make New Friends

How 'real' connection is defined

Waldinger defines real connection, and isolation, by the number of "secure attachments" a person has. How many friends could you call in the middle of the night if you were sick or scared? The percentage of people reporting zero such people (including many who are married) rose from three percent in 1990 to 12 percent in 2021. The percentage with 10 or more such close friends dropped from 33 percent in 1990 to 13 percent in 2021.

Waldinger explains the statistical methodology used to correlate isolation to diseases as varied as heart disease and Type 1 diabetes. They also now run study participants through tests that measure their ability to withstand stressful situations and come back to normal levels of blood pressure, heart rate, and heart rate variability. Resilience under stress, it turns out, is directly correlated to a social network (lonely people react more strongly to stress and take a lot longer to come back to calm).

RELATED: 13 Things The Most Popular People Do When They Want To Make New Friends

The loneliness factor

The "loneliness factor," he explains, has evolutionary routes. Natural selection chooses those ancestors who lived in groups. Whenever these socially connected ancestors found themselves alone they went into hyper-stimulated mode looking for danger and trying to get back to their tribe. It was hard-wired into them. And is still hard-wired into us.

That hyper-stimulation of the brain and body when we are chronically alone is what causes not just bad mental health outcomes (suicide), or death by addiction (OD or just destruction of the body over time), but pretty much every other major disease category from cancer to heart disease. There are many other important risk factors that are highly correlated with these diseases.

But chronic isolation, when examined head-to-head with every other risk factor, is the most important according to Waldinger when looking at this 85 years of data.

RELATED: 7 Subtle Signs You're Suffering From Chronic Loneliness

Vulnerability is the answer

I recently wrote about how we as men too often find ourselves dominated by our Reptilian Brain resulting in negative and self-destructive patterns of behavior. And how for us as men, vulnerability is the answer.

Waldinger is talking about exactly the same thing. When we are alone we are hyper-aroused spending all our time in the primitive reptilian brain which, it turns out, not only causes us to do all kinds of stupid things but also, science proves, will kill us. The answer is to be vulnerable, to connect. In the recovery world, we say that our disease "wants us alone and dead." I guess that is true of all of us. Men and women, addicted or not.

Social media, Waldinger points out, has been an accelerator of isolation. Even in academic circles, thought leaders bully and troll each other. We all have FOMO and are susceptible to those tiny dopamine hits Zuckerman and all the rest of them have master-minded. Waldinger confesses that when he and his wife get up in the morning and drink their coffee, they are both glued to their phones like the rest of the country.

RELATED: Why You Need To Be Grateful For All Of Your Friendships

How to find your calm center — and get out of your own head

Recently I have been exploring breathwork with an old friend from the gym Iona who has devoted her life to teaching the practice. I have found it very powerful. Equally powerful has been her suggestion to go for extended periods of technology detox.

I have been experimenting with going from 5 a.m. to 3 p.m. on weekends turning everything off (phone, computer, internet, etc.). The moment I did it the first time, I felt enormous relief. My nervous system calmed right down. I was safe in a way that I hadn't been in a long time.

Waldinger is talking about getting out of our heads and into our hearts. Iona talks about the body as the bridge to the soul. I do crazy things like swim in Boston harbor when it's 40 degrees because it allows me to get out of my head and into my body. Turn off that over-stimulated flight or fight response.

Waldinger's solutions are pretty simple. He is in favor of some kind of national service for young people that would allow them to connect with a diverse group of peers. He encourages us to think of one person we miss every day and call or text that person.

He favors architecture and workplaces that promote casual interaction with other humans. And he asks us to think of our "social" fitness as even more important than our athletic fitness. It's a muscle that needs work every day.

And if you are lonely never, ever feel like you are the only one. The whole country is lonely. We just need to start talking about it a whole lot more.

RELATED: How To Avoid Forced Friendships And Let Things Develop Naturally

Tom Matlack has been depressed, a drunk, anorexic...and yet at 58 he has never been happier. He adores his wife and three kids. His mission is to help men. He writes daily at Substack. 

This article was originally published at LinkedIn. Reprinted with permission from the author.