Renee Onque

An 87-year-long Harvard study found that social fitness — maintaining your personal relationships and keeping them in good shape — was the No. 1 thing the happiest, longest-living people have in common.

"Invest in relationships, invest in connections and invest in the things you find meaningful," Dr. Robert Waldinger, the director of the Harvard Study of Adult Development, said during an interview at the New York Times Well Festival.

"If you're doing more of that, you're more likely to be happy more of the time. You won't be happy all the time. But happiness is likely to find you more often."

To prove that pouring into your connections doesn't have to be a heavy lift, Waldinger offered up a simple way that the audience at the festival could receive a "dopamine hit" and connect with someone in their lives immediately.

"When I talk about investing in relationships, most people think, 'You know, I am so busy. I have so much going on in my life. How do I make time for this?'"

Here's how you can improve a relationship that you value in just three steps:

1. Take out your phone.
2. Think of somebody who you haven't seen in some time or that you'd like to connect with more.
3. Send that person a text or email, saying, "Hi, I was just thinking about you, and I wanted to connect."

"One of the things we found about people who were what we call socially fit is that they did these small things over and over again. You know, daily, multiple times a day," Waldinger said.

During their commute, they'd call someone, or they'd schedule their workouts at the gym with a friend, he explained. They found ways to intertwine the repetitive tasks in their daily life with social connection.

"When people did that, they stayed more current with more people in their lives. And that built this bedrock of social wellbeing."

CNBC