HEALTH problems which run in families are not just due to shared genes - but shared lifestyles and surroundings, according to Scottish research.

Living in the same home and adopting the same habits play a major part in the risk of contracting the same diseases as parents and siblings, say the Edinburgh scientists.

The finding, which raises questions about the importance attached to genetic make-up, is based on the examination of the medical histories of more than 500,000 people and their families.

Records of both blood relations and adopted children were included in the study.

The researchers based at Edinburgh University's Roslin Institute and MRC Human Genetics Unit looked at incidence of 12 common diseases including high blood pressure, heart disease, several cancers and dementia in volunteers who belong to the UK Biobank.

They conclude that by failing to account for shared environmental factors, scientists may overestimate the importance of genetic variation in health issues by an average of 47 per cent.

Experts say their findings will help to provide realistic expectations of the value of genetic testing for identifying people at risk of disease in future.

The research, published in the journal Nature Genetics, also underlines the need to identify different disease triggers and investigate how to address them to prevent ill health.

Professor Chris Haley, of the MRC Human Genetics Unit, said while some factors may be well known - such as choice of diet and exercise habits - there may be other factors which see members of one family afflicted with the same health issues which have not been considered. Exposure to the same viruses is one possibility.

He said: "With some diseases the environmental factors are more important than the genetic factors in terms of generating similarity with family members... Some of the things we know from other studies are important like diet and exercise in heart disease. But there may be things in there we do not yet know about and it will spur further research about what those factors are and what we can do to alleviate them."

For lung cancer, he said, genes appeared to play a very small role - about 10 per cent. For other conditions such as dementia, stroke and Parkinson’s disease the family environment appeared to be of limited importance.

Professor Haley added: “The huge UK Biobank study allowed us to obtain very precise estimates of the role of genetics in these important diseases."

The study was supported by the Biotechnology and Biological Sciences Research Council and the Medical Research Council.