Women who live alone with their children are 70% more likely to suffer premature death, they found.

The study of more than 700,000 women in Sweden suggested suicides, violence and alcohol-related death were the biggest causes of increased risk to lone mothers.

The number of single mums has increased significantly over the past few decades - in Sweden, 20% of families are now headed by a lone parent.

The excess risk of death remained after adjusting the findings taking into consideration economic status and previous medical records.

Though financial, social and health disadvantages played a part, there was a risk of death independent of these factors, said Gunilla Ringback Weitoft of the National Board of Health and Welfare in Stockholm, who led the research.

Lone mothers were six times more likely to receive social welfare and two times more likely to receive unemployment benefit than mothers who lived with a partner.

Lone mothers were more likely to work full-time and on average worked longer hours, increasing the stresses on them, Weitoft said in the Lancet medical journal.

Risk of suicide

Their risk of suicide was four times higher and their risk of being a victim of domestic violence was five times higher.

Weitoft said: "Psychological stress, stigma and financial difficulties associated with lone parenthood have adverse health consequences.

"For previously married people, the stress suffered during marital breakdown also contributes."

But she added that getting out of a failing or abusive marriage may sometimes be in the woman's best interest.

"An intact marriage is no guarantee of an emotionally healthy, well-supervised home environment," she said.

Francis McGlone, a senior research officer at the Family Policy Studies Centre, an independent charity based in London, said the study's findings did not surprise him.

He said: "For lone parents and their children, negative outcomes are associated with that sort of family environment.

"As much as half of that may be due to poverty. Living in that poverty will increase their chances of early death."

The stresses of being a lone parent were bad for both mothers and their children, he added.

"We know that being married is an amazing protector."