Becoming parents lengthens people's lives as it makes them behave more responsibly, take fewer risks and follow healthier lifestyles, a study suggests.

The study of 21,000 couples treated at IVF clinics in Denmark found the death rate from cancer, heart disease and accidents was four times higher among childless women than among those who had children.

Among men, death rates were twice as high among those who did not become parents. The findings are published in the Journal of Epidemiology.