Long relationships - not necessarily marriage - are a key to good health, according to new research conducted on New Zealanders.
Men and women who are in relationships for longer than five years are less likely to be depressed, to consider or attempt suicide, or to be dependent on alcohol or drugs, Otago University researchers found.
"Marriage is known to be associated with improved mental health, but little research has examined whether the duration of a cohabiting relationship is associated with mental health," said Sheree Gibb, who led a team which examined the associations between relationship duration and mental health problems in a group of 1000 30-year-olds tracked since their birth in Dunedin.
Dr Gibb said the study found the legal status of the relationship did not make a difference: it was the length of the relationship that had a positive effect on people's mental health - and it did not matter if the couple was married or simply living together.
This was a contrast to previous studies, which had reported lower rates of mental health problems among people in legal marriages than in cohabiting relationships.
The study, published in the British Journal of Psychiatry, found that longer relationships were associated with lower rates of mental health problems, the Telegraph newspaper in Britain reported.
"Our study suggests that partner relationships are protective for mental health, with the protective effect increasing as the length of the relationship increases," Dr Gibb said.
"This could be because emotional support and financial stability tends to increase over the course of a relationship."
At the age of 30, 16 per cent of people who were not in a relationship showed symptoms of depression along with 23 per cent of people who had been in a relationship for less than two years.
The rate was less than 10 per cent among people who had been in a relationship for between two and four years and was 9 per cent among people who had been in a relationship lasting more than five years. The researchers relied on the participants reporting their own mental health and relationship status.
The study also found that the rate of alcohol abuse or dependence was 12 per cent among 30-year-olds who were not in a relationship and 13.5 per cent for people who had been in a relationship for less than two years.
In comparison, only 4 per cent of those who had been in a relationship for between two and four years had alcohol problems and less than 3 per cent for those who had been in a relationship for more than five years.
The researchers found that this association remained after they controlled for other factors, such as family background and previous mental health problems.
"People who are at high risk of developing mental health problems may benefit from efforts to improve the stability and duration of their partner relationships, such as improved access to relationship-counselling services," Dr Gibb said.