In a pair of studies involving nearly 280 000 people, William Chopik of Michigan State University in the US found that friendships become increasingly important to one's happiness and health across one's lifespan.
"Friendships become even more important as we age," said Chopik.
For the first study, Chopik analysed survey information about relationships and self-rated health and happiness from 271 053 participants of all ages from nearly 100 countries.
The second study looked at data from a separate survey about relationship support/strain and chronic illness from 7481 older adults in the US.
According to the first study, both family and friend relationships were linked to better health and happiness overall, but only friendships became a stronger predictor of health and happiness at advanced ages.
The second study also showed that friendships were very influential – when friends were the source of strain, participants reported more chronic illnesses and when friends were the source of support, participants were happier.
That may be because of the optional nature of relationships – over time, we keep the friends we like and who make us feel good and discard the rest, according to the findings published online in the journal Personal Relationships.
Friends also can provide a source of support for people who do not have spouses or for those who do not lean on family in times of need.
Friends can also help prevent loneliness in older adults who may experience bereavement and often rediscover their social lives after they retire.
Family relationships are often enjoyable too, Chopik said, but sometimes they involve serious, negative and monotonous interactions.
"There are now a few studies starting to show just how important friendships can be for older adults. Summaries of these studies show that friendships predict day-to-day happiness more and ultimately how long we'll live more so than spousal and family relationships," he said.