At Decoding keys to a healthy life | Harvard Gazette they say,
according to Robert Waldinger, director of the Harvard Study of Adult Development, "We used to think that if you had relatives who lived to a ripe old age, that was the best predictor" of a long life. It turns out that the lifestyle choices people make in midlife are a more important predictor of how long you live."

In Waldiner's Ted Talk he says.

Good Relationships are the most important thing in happiness, health and longevity.:
The quality of relationships is more important than the number.
You can argue and fight, but if you know you can rely on each other,
that is what counts.

20% of people describe themselves as lonely