The growing phenomenon of loneliness, which international experts have described as a global epidemic, may be responsible for as many deaths as obesity, according to the results of two meta-analyses presented at the annual convention of the American Psychological Association in Washington.

To examine the impact of social isolation and solitude on the risk of premature mortality, researchers conducted an initial meta-analysis of 148 studies that involved 300,000 participants.

The results confirmed the longevity benefits of a rich social life: a greater social connection is associated with a 50 per cent reduction in the risk of premature mortality.

A second meta-analysis that brought together data from 70 studies involving some 3.4 million individuals, mainly in North America, but also in Europe, Asia and Australia, highlighted the same conclusions and drew attention to a major cause for concern: social isolation and solitude constitute risk factors that are at least as significant as others that have been previously identified, like obesity.

"With an increasing aging population, the effect on public health [of social isolation] is only anticipated to increase," explains the lead author of the analysis, Dr Julianne Holt-Lunstad, Professor of Psychology at Brigham Young University, Utah.

Previous studies have shown that social isolation is not good for the heart or arteries. In 2016, researchers at the University of York in England found that people living alone faced a 29 per cent greater risk of heart attack and angina, and a 32 per cent greater risk of stroke.

Researchers have demonstrated that loneliness has an impact on lifestyle including on high blood pressure, high cholesterol counts, and diabetes. People who live alone tend to exercise less, smoke more, and eat a less well-balanced diet.

Social involvement in activities, like in the pursuit of hobbies or spending time with family and friends, is one of the keys to good health and psychological wellbeing.

The researchers recommended that people should prepare for retirement socially as well as financially, as for many people, the workplace is their biggest source of companionship.

In the United States, the most recent census found that more than a quarter of the population lives alone.

In France, a 2016 study conducted by Crédoc for the Fondation de France found that social isolation affects one person in 10.