When Friedrich Nietzsche declared "that which does not kill us makes us stronger", he probably did not have parenthood in mind.

Yet a new study suggests despite the sleepless nights, incessant worry and financial headaches that children bring, youngsters also increase longevity.

In fact, fathers can expect to live nearly two years longer than childless men, while mothers gain an extra 18 months.

Scientists believe the effect is the result of a loving support network that is crucial in later life, when something as simple as a fall can be deadly.

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People with a close-knit family are also generally encouraged by loved ones to visit the doctor, stay active and take care of themselves.

Previous studies have found that loneliness or losing a partner in later life can hasten death, but it is the first large survey to show that children have a protective effect.

Dr Karin Modig, of the institute of environmental medicine at the Karolinska Institutet, in Stockholm, which carried out the study, said: "Having children is associated with increased longevity, particularly in an absolute sense in old age. Support from adult children to ageing parents may be of importance for parental health and longevity. At old age, the stress of parenthood is likely to be lower and instead, parents can benefit from social support from their children."

To find out if parenthood might help to stave off death in later years, researchers studied the records of nearly 1.5 million people who were born as early as 1911, looking at when they died and whether they had children.

The risk of death rose with increasing age, irrespective of whether the individuals were parents or not.

But after taking account of influential factors, such as educational achievement and deprivation, life expectancy was higher among those who had children.

The findings contradict previous studies that suggest, for women at least, children shorten lifespan. In poor communities, having four or more children has been shown to shorten lifespan by 3.5 years.

The new study found that mothers lived on average to 84.6, compared with women without children whose life expectancy was 83.1.

The difference was more striking for fathers, whose life expectancy was 80.2 instead of 78.4 compared with childless men.

The gap in death risks between the two groups also rose with increasing age, and was larger for men than women.