All of these studies, as well as our own Harvard Study, bear witness to the importance of human connections. They show that people who are more connected to family, to friends, and to community, are happier and physically healthier than people who are less well connected. People who are more isolated than they want to be find their health declining sooner than people who feel connected to others. Lonely people also live shorter lives. Sadly, this sense of disconnection from others is growing across the world. About one in four Americans report feeling lonely—more than sixty million people. In China, loneliness among older adults has markedly increased in recent years, and Great Britain has appointed a minister of loneliness to address what has become a major public health challenge.

Loneliness is more pervasive than ever before, and our ancient brains, designed to seek the safety of groups, experience those negative feelings as life-threatening, which leads to stress and sickness.

The same is true for social fitness.

It’s not easy to take care of our relationships today, and in fact, we tend to think that once we establish friendships and intimate relationships, they will take care of themselves. But like muscles, neglected relationships atrophy. Our social life is a living system. And it needs exercise. You don’t have to examine scientific findings to recognize that relationships affect you physically. All you have to do is notice the invigoration you feel when you believe someone has really understood you during a good conversation, or notice the tension and distress after an argument, or the lack of sleep during a period of romantic strife.

If we feel disconnected from others at work, that means we feel lonely for the majority of our waking hours. This is a health concern. As we’ve mentioned elsewhere, loneliness increases our risk of death as much as smoking or obesity. If we find ourselves feeling lonely at work, it may be up to us to create opportunities for social connection to the extent that we can. For parents raising their kids at home, play dates or visits to a local park (which are often as much for the parents as for the kids) can be restorative. For warehouse workers, there may be opportunities to connect with people directly before a shift, or directly after.

The power of friendship isn’t just the stuff of anecdotes or philosophical observation; science has clearly shown this effect. Friends diminish our perception of hardship—making us perceive adverse events as less stressful than we might otherwise see them—and even when we do experience extreme stress, friends can diminish its impact and duration. We feel the stress, but with the help of friends we’re better able to manage it. Less stress and better stress management lead to less wear and tear on our bodies.

Friends, in short, keep us healthier.

In Chapter Two we discussed a 2010 review conducted by Julianne Holt-Lunstad and others that brought together 148 studies and a vast amount of data to analyze the effect that social connections have on health and longevity. Among those 148 studies were a number that focused specifically on friendship. Here are a few that make the point:

• A large longitudinal study in Australia found that people over 70 with the strongest network of friends were 22 percent less likely to die during the study period (ten years) than those with the weakest network of friends

• A longitudinal study of 2,835 nurses with breast cancer found that women who had ten or more friends were four times more likely to survive than women who had no close friends.

• A longitudinal study of over 17,000 men and women between the ages of 29 and 74 in Sweden found that stronger social connections decreased the risk of dying from all causes by almost a fourth over a period of six years.