Women who do not have children risk dying earlier and suffering poorer health in later life, according to research to be published today.

Childless women aged 50 and over are 20% more likely to die in any given year than those of the same age who have given birth twice.

But two to four children is the optimum for a woman's health, with women who have five or more children and teenage mothers also having an increased risk of early death and poor health. In a blow to critics of late motherhood, women who delay having their first child until they are 40 or over also appear to enjoy the best health.

The findings emerged from an analysis of three population-wide studies monitoring almost 100,000 women in the UK and the US.

The largest data set covered 1% of the population of England and Wales born between 1911 and 1940 - around 85,000 women. Another British survey from the Medical Research Council provided detailed information on about 1,500 women born in 1946, while a third study, from the US, assessed changes in health, employment, income and wealth for some 5,000 women born between 1931 and 1941.

The researchers, led by Professor Emily Grundy, a gerontologist at the School of Hygiene and Tropical Medicine in London, also found that leaving less than 18 months between children was associated with poorer health, though this only occurred for the oldest women - those born between 1911 and 1920 - suggesting it may be due to poor nutrition at the time.

Mothers who had children before turning 21 were also more likely to suffer from mental illness in later life, with an 11% risk of depression at the age of 53, compared with 7% for those who had had their first child later.

But women who delayed having a baby until they were 40 or over appeared to enjoy the best health, with them being less likely to die after they were 50 and 30% less likely to suffer from long-term illness compared with younger mothers.