Marriage can help protect people from heart diseases or strokes, as well as reduce the risk of death from these conditions, a study claims.

Published in the journal Heart, the study is the largest to date, with the age and ethnicity of the participants strengthening the wider applicability of the findings, researchers said.

Previous research on the impact of marital status have yielded somewhat mixed results. In a bid to clarify the issues, scientists trawled research databases for relevant published studies.

About 80 per cent of cardiovascular diseases can be attributed to well-known risk factors like age, sex, high blood pressure, high cholesterol, smoking and diabetes. However, it is not clear what influences the remaining 20 per cent.

Researchers from Keele University in the UK drew on past research that involved more than 2 million people aged between 42 and 77 from Europe, Scandinavia, North America, the Middle East, and Asia.

Pooled analysis of the data revealed that those who were widowed, divorced or never married were at heightened risk of developing cardiovascular disease and coronary artery heart disease.

Not being married was also associated with a heightened risk of dying from both coronary heart disease and stroke.

When the data was further broken down, the analysis showed that divorce was associated with a 35 per cent higher risk of developing heart disease for both men and women, while widowers of both sexes were 16 per cent more likely to have a stroke.

While there was no difference in the risk of death following a stroke between the married and the unmarried, this was not the case after a heart attack, the risk of which was significantly higher, around 42 per cent, among those who had never married.

Researchers cautioned that the methods used and adjustments made for potentially influential factors varied considerably across all the studies, which may have affected the results of their analysis.

There was no information on same-sex partnerships or the quality of marriage. The potential role of living with someone, as opposed to being married to them, was not explored either.

There are various theories as to why marriage may be protective, researchers said.

These include earlier recognition of, and response to, health problems; better adherence to medication, better financial security, enhanced wellbeing, and better friendship networks.

"Future research should focus around whether marital status is a surrogate marker for other adverse health behaviour or cardiovascular risk profiles that underlies our reported findings or whether marital status should be considered as a risk factor by itself," researchers said.