John Gallacher, a Cardiff University academic who reviewed the European studies, said the happily married were more likely to eat healthily, have more friends and take better care of each other. ‘Marriage and other forms of partnership can be placed along a sliding scale of commitment, with greater commitment conferring greater benefit,’ he added. ‘That marriage generally indicates a deeper commitment might explain why marriage is associated with better mental health outcomes than cohabiting. Cohabiting relationships tend to be less enduring. The most widely accepted explanation is that being in a committed relationship means better social support is available. Commitment seems to provide networks of supportive and helpful relationships, beginning with the spouse or partner, leading to more healthy lifestyles and better emotional and physical health.’

Dr Gallacher warned that difficult and strained relationships were bad for mental health, and being single was better than being in a strained relationship. ‘The take home message is simple. Exclusive and supportive relationships confer substantial mental and physical health benefits that grow over time,’ he added. ‘Although failure of a relationship can harm health, that is an argument for avoiding a bad relationship rather than not getting into a relationship at all. On balance, it is probably worth making the effort,’ he said.