Background: 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.
Aims: To examine the associations between relationship duration and mental health problems in a birth cohort of 30-year-olds.
Method: Associations between relationship duration and mental health were examined using a generalised estimating equation approach. Associations were adjusted for covariates, including prior mental health problems.
Results: Longer relationship duration was significantly associated with lower rates of depression, suicidal behaviour and substance abuse/dependence, even after adjustment for covariates. In most cases the associations did not vary with gender. Legal relationship status (legally or de facto married) was not significantly related to mental health once due allowance was made for relationship duration.
Conclusions: Increasing relationship duration, but not legal relationship status, has a protective effect on mental health for men and women.