Image caption There are many ways in which friends can boost health and wellbeing

Having a good network of friends and neighbours boosts survival chances by 50%, US researchers believe.

The Brigham Young University team came to this figure by number-crunching data from nearly 150 studies looking at survival odds and social networks.

And they calculate that having few friends is as damaging to survival as smoking 15 cigarettes a day or being alcoholic, PLoS Medicine reports.

They believe caring about others makes us take better care of ourselves.

But they warn that in today's modern world social networks are deteriorating as we struggle to juggle careers and families and find a happy work-life balance.

Relationships sustain us and help our mental health and wellbeing Christine Northam, Relate counsellor

Losing this social support, they say, cuts survival odds far more than being obese or not exercising.

Lead researcher Julianne Holt-Lundstad says there are many ways in which friends, colleagues and family can boost health and wellbeing.

"When someone is connected to a group and feels responsibility for other people, that sense of purpose and meaning translates to taking better care of themselves and taking fewer risks."

In their study, which looked at over 300,000 people from four continents over a period of seven years, those with the strongest social networks fared best in terms of health outcomes and lifespan. They were nearly twice (1.5 times) as likely to be alive at any given age than those who were lonely.

The study included people of all ages and backgrounds, yet the findings remained the same and regardless of initial health status.

Co-researcher Timothy Smith said: "The effect is not isolated to older adults. Relationships provide a level of protection across all ages."

But he warned that modern conveniences and technology can lead some people to think that face-to-face social networks are not necessary.

Social networking

"We take relationships for granted as humans - we're like fish that don't notice the water. That constant interaction is not only beneficial psychologically but directly to our physical health."

Christine Northam, a counsellor for Relate, said friendship was essential to human survival.

"We are designed to live and work in groups. It starts in childhood with our family, then school widens our social network.

"Relationships sustain us and help our mental health and wellbeing. Isolation, on the other hand, is linked with mental illness, anxiety and ill health."

Michelle Mitchell of Age UK said illness could be a barrier to maintaining social networks.

"It's well known that social relationships are extremely important to older people's wellbeing, yet sadly one-in-10 over-65s say they always or often feel lonely.

"Many people in later life struggle to maintain social networks due to mobility difficulties, access to transport or following the death of a spouse. The isolation and loneliness many face can also lead to symptoms of depression, affecting one-in-four older people.

She said Age Concerns across the country offer older people a place to socialise and meet new people. "We run a range of activities such as lunch clubs, computer courses and exercise classes, as well as one-to-one befriending schemes for people who need extra support."

Professor Sally Macintyre, director of the Medical Research Council's Social and Public Health Sciences Unit, said: "Policymakers and health care staff should note this important finding, and we need to build on it to find out how we can use social relationships to reduce the risk of death."