When things get busy, our friends often get short shrift. Whether we’re caught up in a positive thing (a new romantic relationship), a not-so-positive one (tending to an ill family member), or just the everyday hustle-bustle of work and family—we assume the catch-up call with a friend can wait.

Not only do the friendships suffer; we suffer, too.

That’s because friendships aren’t just nice to have; they’re a key factor in our long-term mental, physical, and emotional health. “The strength of your relationships has been found to have very concrete ramifications on health—including the health of your cardiovascular system, immune system, and levels of inflammation,” says Lydia Denworth, science journalist and author of “Friendship: The Evolution, Biology, and Extraordinary Power of Life’s Fundamental Bond.” “It also affects your quality of sleep, your risks of depression and dementia, your response to stress, and even the rate at which your cells age.”

Perhaps the clearest evidence of the power of friendships comes from the Harvard Adult Development Study, which followed the males in a Harvard undergraduate class (that included President John F. Kennedy) from their late teens all the way through their 80s. The best predictor of those men being healthy and happy at 80 wasn’t their cholesterol levels, their physical activity levels, or their wealth; it was the level of satisfaction they had with their relationships.

Keep that in mind the next time you feel too busy to reach out or don’t think you can take one more Zoom call. Here are five strategies for keeping your vital friendships robust and alive—even from a distance.

1. Take stock. 

Friendships must be reciprocal and cooperative to thrive, says Denworth. Think back to your last conversation with one of your friends. Who did most of the talking? Who usually does? Or is it a fairly even exchange? “It’s not an exact tit-for-tat accounting where I talk for 10 minutes, then you talk for 10 minutes,” Denworth says. “While you will each face crises at different times, a sense of equity over the long haul in a relationship is crucial.”

2. Be an attentive listener.

Being a good friend means offering the gift of your full attention. “We have a tendency to want to fix problems or relate what our friends are going through to our own experience,” Denworth says. “We’re often not really listening. We’re waiting to tell our own story.” Before you jump in with an opinion or solution, make it a point to ask at least three questions first—and one of them should be: “Do you just want me to just listen, or are you looking for advice?” And then, honor their wishes.

3. Be a positive force in their life.

Positivity is a critical ingredient of friendship. Find ways to express and share positive vibes regularly—whether that means telling your friends what they mean to you or sharing an article or funny video that makes you think of them. An actual gift speaks volumes. “It’s not about how much money you spend, it’s about showing someone you care about them and you’re paying attention to what they like and need.”

4. Show up.

For your friendship to thrive in the long haul, you’ve got to show up consistently, both literally and figuratively: being present for birthdays and funerals (even if that means in a socially distanced way); honoring the plans you make; and being present to them when you can’t be with them in real-time—via texts, emails, or cards (remember cards?!). Showing up in even the smallest ways counts, and they won’t forget it.

5. Clear out the gray zone. 

Research shows that about half of our social circles consist of relationships we don’t feel strongly about one way or another, Denworth says. But ambivalent connections can eat up time and energy that we’d otherwise spend on closer friendships. For those folks who fall in the gray area, ask yourself if you’re ready to invest a little time in making them more fulfilling, or let that relationship go—so you can be a better friend to the ones that matter most.