Coughs and sneezes spread diseases - but not among friends

The workaholic, the lonely widow and the social misfit share a common weakness, researchers have found. Their lack of social ties makes them more vulnerable to the common cold.

People with a wide range of social relationships are less likely to catch colds and suffer fewer symptoms than those whose social life is more narrowly based, a study has shown.

However, friends alone are not enough to confer protection. Scientists at Carnegie Mellon University in Pittsburgh, US, who administered cold viruses to 276 healthy volunteers aged 18 to 55, found it was the diversity of social ties, rather than their quantity, that mattered. Those with a range of different relationships - with family, friends, community groups and work colleagues - were less susceptible to colds, produced less mucous and shed less virus than those whose lives were focused on one type, such as home or work.

Dr Sheldon Cohen, who led the study, said 12 social roles were defined, including spouse, parent, child, parent-in-law, and member of work, school or religious group. Friends were defined as someone in contact at least once every two weeks.

"Whether you have one friend or 20 makes no difference, that is only one kind of social tie. It is not the number of relationships but their diversity that counts," he said.

Those who said they had between one and three types of relationship had more than four times the risk of contracting colds, compared with those who said they had six or more types of relationships, the researchers report in the Journal of the American Medical Association. The difference in risk remained even after smoking, drinking and consumption of vitamin C were taken into account.

Dr Sheldon said the findings supported other evidence suggesting people with more kinds of social tie live longer. In Britain, life expectancy for men aged 25 to 39 has fallen for the first time this century. The rising divorce rate, family break-ups and loneliness are thought to be partly to blame.

The authors say people with broader social contacts may have a greater sense of responsibility and self-worth which encourages them to take more care of their health and makes them less prone to anxiety and depression. There are also hormonal effects that may strengthen the immune system.

Dr Sheldon said: "If your life is work and you have no family or friends and something goes wrong at work, your whole concept of yourself is blown. But if your work is just a part of your life and you have family and friends, go to a bowling group or to church, of course you will be upset if something goes wrong at work but it doesn't destroy your world."

"It has to do with how people view the world and the impact things going wrong in any part of it have on them."