When we think about taking care of ourselves, we think about eating better, sleeping, moving, getting to the doctor on time. We almost never think about who we’re going to see on Saturday, and it turns out that weighs as much as the rest, sometimes more. The people we spend our days with aren’t the backdrop of life; they’re a good part of life itself, and of how it goes for us.

There’s a Harvard study that made it pretty clear, one of the longest ever done on happiness: it began more than eighty years ago and followed the same people across their whole lives, decade after decade, into old age. When the researchers gathered everything they knew, what best predicted who would reach eighty healthy and content wasn’t cholesterol or blood pressure at fifty. It was how satisfied they were with their relationships. Good relationships, they concluded, keep us healthier and happier. As simple as that, and as easy to forget.

And it isn’t about having a ton of people around; it isn’t a matter of quantity. You can be surrounded and feel alone, or have three real people and feel at home. What sustains us isn’t the number, it’s the sense that someone truly sees you, listens without being half there, someone you can be around without having to perform. That, which sounds so basic, is one of the hardest things to find  and one of the things that holds us up the most.

It makes sense that it weighs so much on the body. Having someone to tell things to turns down the noise, calms that alarm that goes off when something’s wrong; it’s like having somewhere to lean when the day hits hard. And the reverse is true too: the relationship that keeps you on edge, the one that’s a roller coaster of very good and very bad, wears you down in a way that eventually shows. Not everything around us adds up. There’s company that rests you and company that drains you, and the body knows the difference even when the head takes a while.

The other thing we forget is that relationships don’t keep themselves. They’re like a plant: if you don’t water it, it dries up, however good it once was. And you don’t water it with grand gestures, but with the boring and constant: showing up, calling for no reason, remembering, giving time even when you arrive tired. The friendship we took for granted is one day no longer there, not from a fight, but from neglect, from letting it slide. Taking care of the people we love is less epic than it sounds and more everyday: it’s being there.

That’s why it’s worth seeing it for what it is: taking care of the people close to us is also taking care of ourselves. As much as the salad and the walk, maybe more. And the good part is that it’s never too late to water what had dried out a little, or to reach out to someone we hadn’t seen in a while. In the end, a good part of how life goes for us has the shape of the people we give our time and our attention to. Worth choosing them well, and once chosen, not letting them go.