Married couples appear to live longer than singles, according to US research.
After studying almost 5000 people born in the 1940s, researchers from the Duke University Medical Centre found people who never married had twice the risk of dying early than those who had been married most of their adult life.
The researchers took personality and risky behaviour into consideration, but still found being married or having a stable long-term partner was the greatest protector against early death.
Losing a partner and not re-marrying also increased the risk of early death during middle age.
"Our results suggest that attention to non-marital patterns of partnership is likely to become more important for these baby boomers," author Dr Ilene Siegler and her colleagues wrote.
"These patterns appear to provide different levels of emotional and functional social support, which has been shown to be related to mortality. Social ties during midlife are important to help us understand premature mortality."
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Previous research has found people who have been in relationships for more than five years are less likely to suffer depression, attempt suicide or have drug and alcohol problems.
Dr Christina Bryant, from the School of Psychological Sciences at the University of Melbourne, told ninemsn positive relationships have long been known to be good for our health.
"Within marriage or a stable intimate partnership, it probably works partly through the emotional confiding, but also practical support and practical incentives for the up-take of healthy behaviours," she said.
"It possibly motivates you to eat healthily and there is an external control on your drinking and your exercise. People may also undertake healthy behaviours together."
Dr Bryant said strong relationships also help people deal with stress.
"When you have support it acts as a buffer between you and stress," she said.
However she pointed out that there are a lot of other factors that influence our health.
"When you look at the literature on good general health, there are all sorts of factors that are important, ranging from professional employment through to smoking, diet and physical activity," she said.
Past studies have found that strong friendships can also increase longevity in women.
"Having more emotionally confiding relationships with female friends also seems to be very good for your health," she said.
"It's important to be emotionally connected."
The research was published in the journal Annals of Behavioral Medicine.