Good relationships.

In fact, good relationships are significant enough that if we had to take all eighty-four years of the Harvard Study and boil it down to a single principle for living, one life investment that is supported by similar findings across a wide variety of other studies, it would be this:

Good relationships keep us healthier and happier. Period. So if you’re going to make that one choice, that single decision that could best ensure your own health and happiness, science tells us that your choice should be to cultivate warm relationships.

Instead, it is the quality of your relationships that matters. Simply put, living in the midst of warm relationships is protective of both mind and body.

This is an important concept, the concept of protection. Life is hard, and sometimes it comes at you in full attack mode. Warm, connected relationships protect against the slings and arrows of life and of getting old.

Once we had followed the people in the Harvard Study all the way into their 80s, we wanted to look back at them at midlife to see if we could predict who was going to grow into a happy, healthy octogenarian and who wasn’t.

2: Why Relationships Matter

“These feelings, big and small, are connected to biological processes. Just as our brain responds to the presence of food in our bellies by rewarding us with pleasure sensations, so does it respond to positive contact with others. The brain effectively says to us: Yes, more of this, please. Positive interaction tells our bodies that we are safe, reducing our physical arousal and increasing our sense of well-being. By contrast, negative experiences and interactions create a sense that we are in danger and stimulate us to produce stress hormones like adrenaline and cortisol. These hormones are part of a cascade of physical reactions that raise alertness and help us respond to situations of critical importance—the “fight or flight” response. They are a big part of what gives us that feeling of stress.

If we accept the wisdom—and more recently the scientific evidence—that our relationships really are among our most valuable tools for sustaining health and happiness, then choosing to invest time and energy in them becomes vitally important. And an investment in our social fitness isn’t only an investment in our lives as they are now. It is an investment that will affect everything about how we live in the future.

Every workday is an important personal experience, and to the extent we can enrich each one with relationships, we benefit. Work, too, is life.