People who settle down in their 20s are more likely to get a good night's sleep in middle age, according to a new study. 

Researchers at the University of Minnesota also found that they enjoyed lower levels of stress, according to the study published in the Personal Relationships journal. 

The findings may explain why marriage is also linked to a lower risk of premature death, the researchers concluded. 

They examined the quality of sleep and stress levels of 267 people born in Minnesota in 1975-76 who were asked about their romantic relationships at the ages of 23 and 32.

The study found that those who were in relationships early on in life went on to experience less anxiety after the age of 32 and benefitted from better sleep after the age of 37. 

Lead author of the study, Chloe Huelsnitz said: 'The current study is the first to demonstrate stress exposure as a mechanism linking relationship effectiveness to an important health outcome - sleep quality - over time.'

She continued: 'Although the behavioral processes linking relationships and health outcomes are not fully understood, sleep is a shared behavior in many romantic relationships, and it is a strong contender for how relationships 'get under the skin' to affect long-term health outcomes.'

She said the findings added to a growing body of literature supporting the theory that relationships are linked to the 'occurrence and severity of life stress'. 

'Given adults typically share sleeping environments with their romantic partners and given the centrality of romantic relationships in most people's lives, the patterns of behavior and experiences that characterise one's current and past romantic relationships may affect the prevalence of conditions that undermine better sleep,' she said.

She said exposure to stress just 'reduces opportunities for sleep'.

'The findings of our study suggest one way that relationships affect health behavior is through their effects on individuals' stress,' she added.