Dying for company: Loneliness increases mortality risk, says meta-analysis

Claims that loneliness is harmful to our health regularly make media headlines. Certainly, there are plenty of studies that have found links between feeling lonely or being 'socially isolated' — an objective measure of a person's social contacts — and an increased risk of dying prematurely. A 2010 study even famously concluded that loneliness is as damaging to our health as smoking 15 cigarettes a day. 

However, some other large research efforts have not found the same links. Overall, the results to date have been inconsistent, write Yashuang Zhao and colleagues at Harbin Medical University, China, in a new paper in Nature Human Behaviour.

In a bid to get closer to the true picture, the team undertook a massive systematic review and meta-analysis of 90 prospective studies in the field. They used only results from individual analyses that had controlled for as many confounding factors as possible, such as alcohol use, depression or diabetes. 

The team concluded that, among the general population, social isolation (SI) was linked to a 32% increased risk of dying prematurely from all causes. For loneliness, the figure was 14%. They also found that SI was linked to a 24% higher chance of dying from cancer, and a 34% higher risk of dying from cardiovascular disease. Loneliness increased the risk of dying from cancer by 9%. 

The team also reports findings for specific patient groups. Socially isolated people with either breast cancer or cardiovascular disease had a higher risk of dying prematurely from all causes. Also, socially isolated participants with breast cancer were more likely to die from that cancer, compared with patients who had adequate levels of social contact. 

The 90 studies, which had a total of just over 2.2 million participants, consisted of 29 from the US and 61 from other, mostly developed, countries — including the UK. Sixty-seven investigated the risk of dying from any cause in the general population. Seventeen looked specifically at the risk of death from cardiovascular disease or circulatory system diseases, and 11 investigated the risk of dying from cancer, again in the general population. 

A further six studies looked for links between social isolation and the risk of dying from any cause among people diagnosed with either breast or colorectal cancer. A total of seven studies on patients with these cancers investigated whether was an association between social isolation and dying from that cancer, specifically. 

Various ideas have been put forward for why loneliness and social isolation may both be harmful to our health. Socially isolated people could have a poorer diet and do less exercise, for example. SI has also been linked to a higher risk of body-wide inflammation and poorer immune function. Studies have also found ties between loneliness and a higher rate of sleep disorders and immune system dysfunction. 

This new study will increase confidence in the idea that both social isolation and loneliness are indeed harmful to our health. Tackling these problems will mean developing more effective interventions, however, as those that have been tried to date have had limited success. Hopefully, these findings will boost efforts to develop programmes that really do work. 

Read the paper in full: https://doi.org/10.1038/s41562-023-01617-6