"Loneliness as big a killer as obesity and as dangerous as heavy smoking," the Daily Express reports. Researchers pooled the results of previous studies, estimating that loneliness can increase the risk of premature death by around 30%.

The headline follows a new analysis of more than 3.4 million participants, which showed evidence that people who feel, or are, socially isolated or live alone are at about a 30% higher risk of early death.

The study has many strengths: its large sample size, adjustment for initial health status, and use of prospective studies being the main three. This provided some evidence that the isolation was causing ill health, rather than the other way round, but we can't be certain.

Causation bias could still be a factor in some cases – in other words, people with a chronic disease are less likely to socialise with others. This makes it difficult to nail down cause and effect.

The results of this study remind us that health has a strong social element and is not merely physical. Connecting with others can improve both mental and physical wellbeing.

Where did the story come from?

The study was carried out by researchers from Brigham Young University in the US and was funded by grants from the same university.

It was published in the peer-reviewed journal, Association for Psychological Science.

The UK media generally covered the study accurately. Many news sources based their reporting on an assertion made by the lead author, Julianne Holt-Lunstad, who said the harmful effects of loneliness are akin to the harm caused by smoking, obesity or alcohol misuse.

Professor Holt-Lunstad was quoted in the Daily Mail as saying that, "The effect is comparable to obesity, something that public health takes very seriously ... we need to start taking our social relationships more seriously."

This assertion appears to be based on a previous study carried out by Professor Holt-Lunstad published in 2010. We were not able to appraise this study, so we cannot comment on the accuracy of this comparison. The 2010 research was published in the online journal PLOS One.

What kind of research was this?

This was a systematic review and meta-analysis investigating whether loneliness, social isolation, or living alone affects your chances of dying early.

The researchers say there are many lifestyle and environmental factors that increase our risk of dying early, such as smoking, being inactive and air pollution.

However, they say much less attention is paid to social factors, despite evidence they may carry an equal or greater influence on early death.

This study wanted to be the first to quantify the influence of loneliness and social isolation on early death.

What did the research involve?

The researchers searched online databases for studies reporting numerical data on deaths affected by loneliness, social isolation, or living alone. They then pooled all the studies to calculate the overall effect.

The literature search included relevant studies published between January 1980 and February 2014. These were identified using the online databases MEDLINE, CINAHL, PsycINFO, Social Work Abstracts, and Google Scholar.

Loneliness and social isolation were defined objectively and subjectively:

social isolation (objective) – pervasive lack of social contact or communication, participation in social activities, or having a confidant (example measure: Social Isolation Scale or Social Network Index)

living alone (objective) – living alone versus living with others (example measure: answer to a yes/no question on living alone)

loneliness (subjective) – feelings of isolation, disconnectedness and not belonging (example measure: University of California, Los Angeles Loneliness Scale)

Some studies made no adjustment for potential confounders. Others controlled for just a few variables (partial adjustment), usually age and gender.

A final group adjusted for several factors (fully adjusted), such as measures relevant to depression, socioeconomic status, health status, physical activity, smoking, gender and age.

Sensibly, the researchers presented separate results for the different categories of adjustment to see to what extent the results were potentially influenced by the confounders.

The bigger studies counted more towards the meta-analysis than the smaller ones – a "weighted" effect size.

What were the basic results?

In total, the study analysed 70 independent prospective studies containing more than 3.4 million participants followed for an average of seven years. Overall, the researchers found social isolation resulted in a higher likelihood of death, whether measured objectively or subjectively.

Pooling the best studies – those with full adjustment for confounding – showed the increased likelihood of death was 26% for reported loneliness, 29% for social isolation, and 32% for living alone. All were statistically significant increases compared with those reporting less loneliness or social isolation.

The researchers found no differences between measures of objective and subjective social isolation, and the results remained consistent across gender, length of follow-up and world region.

However, initial health status influenced the findings, as did participant age. For example, social deficits were more predictive of death in people under the age of 65 than over 65.

How did the researchers interpret the results?

The researchers said that, "Substantial evidence now indicates that individuals lacking social connections (both objective and subjective social isolation) are at risk for premature mortality.

"The risk associated with social isolation and loneliness is comparable with well-established risk factors for mortality, including those identified by the US Department of Health and Human Services (physical activity, obesity, substance abuse, responsible sexual behaviour, mental health, injury and violence, environmental quality, immunisation, and access to health care)."

They say there is mounting evidence that social isolation and loneliness are increasing in society, so it would be prudent to add social isolation and loneliness to lists of public health concerns.

Conclusion

This meta-analysis of more than 3.4 million participants indicates social isolation, living alone and loneliness are linked with about a 30% higher risk of early death.

The study has many strengths, including its huge sample size, adjustment for initial health status, and use of prospective studies.

This provided some evidence that the isolation was causing ill health, rather than the other way round, but we can't be certain. Poor health can lead to loneliness and social isolation and vice versa, so cause and effect are tricky to nail down.

The researchers believe the study of the effects of loneliness and social isolation is currently at the stage that research into the risks of obesity was decades ago. They have identified a problem and predict it will increase in years to come.

The findings also challenge assumptions. The study team said that, "The data should make researchers call into question the assumption that social isolation among older adults places them at greater risk compared with social isolation among younger adults [who may be at risk of alcohol and drug misuse, as well as suicide].

"Using the aggregate data, we found the opposite to be the case. Middle-age adults were at greater risk of mortality when lonely or living alone than when older adults experienced those same circumstances."

The results of this study remind us all that psychosocial and emotional feelings can be just as relevant to our overall health and wellbeing as physical factors. Read more about how how connecting with others can improve wellbeing and find out how to overcome feelings of loneliness.

Analysis by Bazian

Edited by NHS Website