The risks seem to be greatest for lone mothers in England, the US, Denmark and Sweden, the findings indicate.
The researchers base their findings on the responses of more than 25,000 women aged 50+ to questions about childbearing and marital status; any limitations on their capacity for routine daily activities (ADL), such as personal hygiene and getting dressed, and instrumental daily activities (IADL), such as driving and shopping. They were also asked to rate their own health.
All the women had taken part in one of three biennial nationally representative surveys: the Health and Retirement Study (HRS) in the US; the English Longitudinal Study of Ageing (ELSA in England; or the Survey of Health, Ageing and Retirement in Europe (SHARE).
Thirteen of the 21 countries represented by SHARE (Denmark, Sweden, Austria, France, Germany, Switzerland, Belgium, The Netherlands, Italy, Spain, Greece, Poland, Czech Republic) had collected relevant data.
The researchers wanted to know if single motherhood before the age of 50 was associated with poorer health, and whether going it alone is worse in countries with relatively weak 'social [support] safety nets.'
Single motherhood was classified as having a child under the age of 18 and not being married rather than living with a partner.
One in three of the US mums surveyed had been a single mother before the age of 50, compared with around one in five (22%) in England and Western European countries, around four out of 10 (38%) in Denmark and Sweden, and one in 10 in Southern Europe.
Single mums in every country studied tended to be younger, less well off, and less likely to be married than women who had stayed married throughout their parenthood. In the US and England single mothers also tended to be less well educated.
Analysis of the responses indicated that any period of single motherhood was linked to a greater risk of some level of physical disability and poor health in later life than dual parenthood.
But the associations were stronger for single mums in England, the US, Denmark and Sweden. Single motherhood was less consistently associated with health in Western, Eastern, and Southern European countries.
The analysis indicated that women who became single mothers before the age of 20, or as the result of divorce, or who parented alone for 8 or more years, or who had two or more children, were at particular risk of disability and poor health in later life.
The researchers point out that the findings may reflect 'selection and causation in cycles of disadvantage.' In other words, poverty may increase the risk of single motherhood, perhaps indicating earlier health disadvantages. And lone parenthood may hamper a women's ability to get qualifications, have a career, and earn enough money, which may itself lead to poorer health.
Similarly, social support may partially explain the associations between single motherhood and health, they suggest, noting that in Southern European countries, which have a strong family culture, single motherhood was not linked to increased health risks.
"The findings add to the growing recognition that single motherhood may have long term health effects on mothers. As lone motherhood is on the rise in many countries, policies addressing health disadvantages of lone mothers may be essential to improving women's health and reducing disparities," they write.
And they suggest that adequate access to contraception and policies that help single mums to stay in the workforce and help them balance the demands of work and family, may be very helpful.