“You can choose your friends, but you can’t choose your family.” That line comes from American writer Harper Lee’s book “To Kill a Mockingbird.”

Now compare her words to another famous expression: "Blood is thicker than water." This means that family will always be with you while other people -- with no blood connection -- may come and go.

Having strong ties to family and friends has long been identified as an important part of being happy and healthy. People need people.

However, if forced to choose which is more important, American researchers now say friendship is more important than family. Their new study suggests that friends may be more important than family members, especially as we age.

The study comes from researchers at Michigan State University. They found the importance of friendship on health and happiness grows as people get older.

William Chopik is an assistant professor of psychology at Michigan State and was one of the lead researchers in this study. He says, “friendships become even more important as we age.”

He adds that “keeping a few really good friends around can make a world of difference for our health and well-being."

Chopik notes that we need to think of friendships as an investment in our future happiness.

The Michigan State researchers considered information from two separate surveys. The first involved just over 271,000 subjects. They participated in a study on health and happiness.

The second survey had nearly 7,500 participants. Its purpose was to study “relationship support” in older adults suffering from chronic, or long-term, conditions.

In the first group, both family and friendships influenced overall health and happiness.

However, in the second, researchers said that friendships “became a stronger predictor of health and happiness” as people get older. Also in the second group, unhealthy friendships led to increased chronic conditions. But with supportive friends, Chopik noted, participants reported being happier.

One reason: people can keep the friendships that make them feel good and move on from the ones that don't. Family, on the other hand, will always be with you. They can be helpful and enjoyable, but can also cause troubles.

Chopik explained that “there are now a few studies starting to show just how important friendships can be for older adults.”

In general, he said, they show that friendships affect our day-to-day happiness and how long we live more so than relationships with spouses and family.

Friendships, he added, keep us from being lonely. But keeping a friendship for a long time takes work.

“If a friendship has survived the test of time,” he said, "you know it must be a good one, a person you turn to for help and advice” and a person you want in your life.

This may be good news for people who don't have strong ties with family members. Not all of us are born into the families we need. But we all have the ability to make the friendships that we need.