'Loneliness can be a killer': Why lonely people are at risk of serious health conditions

A team led by scientists at the University of Cambridge, Britain, and Fudan University, China, examined the suite of proteins in blood samples donated by 42,000 adults aged 40-69 who are taking part in the UK Biobank. 

They saw which proteins were present in higher levels among people who were socially isolated or lonely, and how these proteins were connected to poorer health.

When they analysed the proteins and adjusted for factors like age, sex and socioeconomic background, the team found 175 proteins associated with social isolation and 26 associated with loneliness (there was substantial overlap, with about 85% of the proteins associated with loneliness also linked with social isolation).

Many of these proteins are produced in response to inflammation, viral infection, and as part of our immune responses, as well as having been linked to cardiovascular disease, type 2 diabetes, stroke, and early death.

The team explored the causal relationship between social isolation and loneliness, and the proteins. They identified five proteins whose abundance was caused by loneliness. 

Higher levels of one of the proteins, ADM, are linked to increased risk of early death, while another protein, ASGR1, is associated with higher cholesterol and an increased risk of cardiovascular disease.

Other proteins play roles in the development of conditions such as insulin resistance, atherosclerosis (furring of the arteries), and cancer progression.

Dr Chun Shen, from the Department of Clinical Neurosciences at University of Cambridge and the Institute of Science and Technology for Brain-Inspired Intelligence at Fudan University, said: “We know social isolation and loneliness are linked to poorer health, but we’ve never understood why. Our work highlights a number of proteins that appear to play a key role in this relationship, with levels of some proteins in particular increasing as a direct consequence of loneliness.”

Rose Anne Kenny, regius professor of medicine at Trinity College Dublin, welcomes the robust study. Pointing to proteins as the fundamental building block of all our body’s organs — and they are also involved in producing energy in cells — she says: “If things go wrong with proteins, you get diseases within cells, and eventually death of cells.”

Loneliness, says Kenny, is well known to cause heart attacks and stroke, diabetes and early death, as well as dementia. 

“Many, many studies have confirmed that loneliness is strongly linked to these diseases, but we’ve never been entirely sure as to why or how. And what this study has done is take a deep dive in to our very fundamental biology and find the specific proteins most commonly associated with loneliness and social isolation.

“What’s fascinating is that these proteins are also associated with the common diseases we see in loneliness.”

The research, she says, confirms that loneliness leaves a biological footprint, which is toxic. “It confirms a strong biological reason for why loneliness can be a killer.”

The types of loneliness

Dr Joanna McHugh Power, associate professor in psychology at Maynooth University, says the study is progress in loneliness research, but that the quest for a biological explanation for how loneliness and social isolation drive physical ill-health is not new.

McHugh Power says: “We’ve known for a while that loneliness is linked to cardiovascular functioning, blood pressure, hormonal activity, immune function, and how well our genes work in the body. The best theory we currently have comes from the late neuroscientist and social psychologist, John Cacioppo, who was big in to loneliness and how it impacts our bodies. He proposed eight pathways through which loneliness might impact health, including health behaviours, sleep, impaired immunity, and stress.

“For example, in terms of behaviours, if you’re lonely you might drink or smoke more. You might sleep less or have lower-quality sleep. And loneliness can be a stressor, which we know has all these negative, very physical effects,” says McHugh Power, adding that it has also previously been suggested that our genes might drive loneliness and link it with ill-health.

The Cambridge/Fudan University study defined social isolation and loneliness in terms of “impoverished social relationships” and the researchers calculated individual scores for loneliness and social isolation based on whether they lived alone, how frequently they had contact with others socially, and whether they took part in social activities. They also measured whether they ‘felt’ lonely. But this, says McHugh Power, is a “very bare bones” measure of loneliness.

“There’s a lot more to loneliness than just social relationships. We can feel lonely because of a problem in our relationships with other people, if we don’t have enough relationships, or if we’re not finding our relationships satisfying. But we can also feel lonely for a place, for a time, and we can even feel lonely in response to thinking about our own mortality —existential loneliness.”

Additionally, she says seeing the “really important distinction” between social and emotional loneliness is critical. “They are completely different experiences and have different solutions. Social loneliness is more about the need to have a sense of belonging, a social context, a group. Whereas emotional loneliness could be, for example, around the loss of a partner, and you don’t feel you have anybody close to you.

“So we need to properly define loneliness, because otherwise we haven’t a chance of measuring it properly.”

Societal change needed

In November 2023, the World Health Organisation announced a new commission on social connection to address loneliness as a pressing health threat.

Here in Ireland, a June 2024 study, commissioned by Laya Healthcare found that 93% of people believe loneliness is a problem, with 60% feeling lonely at least monthly.

Loneliness disproportionately affects younger people: Those under 44 report feeling lonelier than older demographics, and close to 20% of young adults experience severe loneliness. 

This vulnerability arises from various factors: 44% feel disconnected from those around them, 42% lack sufficient friends and family, and 39% lack social activities.

The study findings did have a ray of hope, though: The Laya Healthcare campaign aims to raise awareness and promote sport, specifically rugby, as a way to help. And, asked whether sport can combat loneliness, 85% of respondents agreed it could.

McHugh Power, who is chair of the Loneliness Taskforce Research Network is concerned about the messaging around loneliness and its health impacts. 

“I have a worry about making people feel responsible for their feelings of loneliness. Saying ‘loneliness is bad for your health, as bad as smoking 15 cigarettes a day’, may cause [affected] people to feel ashamed and shame is not a good driver of positive health change.

“We don’t want people to feel unnecessary shame or anxiety about their loneliness as a result of a message that ‘loneliness is killing you’. Because they may feel stuck and not able to change it — for example, if they’ve poor mobility and are unable to leave the house.”

McHugh Power believes a better approach is to encourage people to be mindful about checking in on those in our lives who might be at higher risk of feeling lonely and also checking in with ourselves as to whether we feel lonely, and if there is anything we can do about it.

“Especially if we have something in our life that might put us at risk. There are all these crunch times in our lives that can [make us more vulnerable], such as being in the postpartum phase, after retirement, or after illness.”

Loneliness is often a driver of increased visits to the GP among older people, and McHugh Power cites the All-Ireland Social Prescribing Network as a really helpful initiative. 

The HSE says this recognises that health is heavily determined by social factors like poverty, isolation, and loneliness: “Social prescribing offers GPs and other health professionals a means of referring people to a range of non-clinical community supports that can have significant benefits for their overall health and wellbeing.”

Kenny, who is the founding principal investigator of the ‘Irish Longitudinal Study on Ageing’, believes a whole-government approach to loneliness is needed, and that any changes made in policy must be checked against their impact on the community, on community living, and community engagement.

“For example, in many villages and towns in Ireland, the post office was the hub of the community. Because it served a number of different functions, it crossed different cohorts in the community: It was where you could meet people.

“And yet, when they [took] post offices out of local communities, no detailed exercise was ever done on the contribution the post office was making to that community. The decision was predicated on finances alone.”

Decisions like these should be made with a whole-government approach, “with responsible government agencies, involved in community and social engagement, being part of any infrastructural change”.

Loneliness is pervasive, and we are making people lonely by creating community-eroding infrastructure.

Kenny says: “I don’t want to accept it anymore. We need to stand up and say, ‘This is not good for our people’. Because we know now we have a disease that’s causing a lot of disability and [adverse] change to our [physical] systems: Like heart disease, stroke, diabetes, dementia.

“And this can be prevented by getting rid of loneliness and social isolation.

“The solution isn’t a drug, but a simple societal change.”