The prevalence of mental ill health was also halved in couples who became adoptive parents, the study shows.

This is not the first time that childlessness has been linked with higher than expected death rates, say the authors.

But the link has traditionally been attributed to unhealthy behaviours and poor mental and physical health, and few studies have differentiated between voluntary and involuntary childlessness, they say.

The researchers base their findings on data obtained from various population registers in Denmark on births and deaths, assisted conception (IVF) procedures, hospital admissions, psychiatric service contacts, plus labour market statistics for the period from 1994 up to 2008.

Between 1994 and 2005, 21,276 childless couples were registered for IVF treatment; 15,210 children were born and 1564 adopted.

During the same period, a total of 96 women and 200 men died, corresponding to a death rate of 51 and 117 per 100, 000 person years, respectively. And 710 women and 553 men were diagnosed with a mental health problem, corresponding to rates of 385 and 299 per 100,000 person years, respectively.

Having a child cut the risk of early death, particularly among women, the analysis showed.

The early death rate from circulatory disease, cancers, and accidents among childless women was four times as high as that among those who gave birth to their own child, and 50% lower among women who adopted.

Similarly, rates of death were around twice as high among men who did not become parents, either biologically or through adoption.

Rates of mental ill health were similar between couples with and without children of their own, with the exception of those with drug and alcohol problems.

But the prevalence of mental illness in couples who adopted kids was around half that of other parents.

Taking account of influential factors, such as age, educational attainment, income and underlying illness had only a marginal impact on the findings.

"Mindful that association is not [the same thing as] causation, our results suggest that the mortality rates are higher in the childless," write the authors. "Rates of psychiatric illness do not appear to vary with childlessness, but the rate of psychiatric illness in parents who adopt is decreased," they add.