What Loneliness Actually Does to Your Health
- 4 days ago
- 17 min read
Updated: 4 hours ago
By: 63° Editorial
August, 2026.
Loneliness is not only about being alone. You can feel it in a crowded school, a busy office, a large family, a relationship or a constantly active group chat. Scientists have spent decades studying what happens when the connection we need is missing, and some of the newest research is making the picture both more compelling and more complicated.
There is an image we tend to associate with loneliness; an older person sitting somewhere alone, perhaps living by themselves, with nobody around. That person can certainly be lonely, but loneliness can look very different. It can be the teenager surrounded by classmates who feels that nobody really knows them, the university student who has met dozens of people but has nobody they would call if something went wrong, or someone who has recently moved to a new city or country and is discovering that building a new life is not the same thing as building a new community. It can be a new parent who spends almost every minute with another human being and somehow feels more isolated than before. It can be someone working remotely from home, an older person whose social world has gradually become smaller, someone inside a large family who does not feel understood, or a person whose phone never seems to stop lighting up.
You can even feel lonely inside a friendship, family or romantic relationship.
That is because psychologists make an important distinction between loneliness and social isolation. Loneliness is subjective. It is the feeling that the relationships or connection you have are not meeting what you want or need. Social isolation is more objective and refers to having relatively few social relationships or interactions.
You can therefore spend a great deal of time alone without feeling lonely, while another person can spend almost no time alone and feel profoundly disconnected. That distinction becomes important when we look at the science because loneliness and social isolation are related, but they are not interchangeable, and researchers are increasingly finding that they may not affect health in exactly the same ways.
A major 2026 study, for example, found only a modest correlation between the two, supporting the idea that they capture overlapping but distinct experiences. So when we ask what loneliness actually does to your health, the answer is more interesting than “loneliness is bad for you.”
One of the longest studies of human life keeps coming back to relationships
Long before loneliness became a public-health headline, researchers at Harvard were following people across their lives and repeatedly finding that relationships mattered.
The Harvard Study of Adult Development began in 1938 with 724 participants from two very different groups in Boston. 268 Harvard College students and 456 young men from disadvantaged Boston neighbourhoods. The study eventually expanded to include spouses and more than 1,300 descendants and has become one of the longest-running in-depth studies of adult physical and mental wellbeing.
Researchers did not simply ask participants whether they were happy. Over decades, the project collected information about physical and mental health, work, relationships and family life as participants moved through adulthood and into old age. When researchers looked back at the participants in middle age and asked what predicted who would be doing well decades later, they found something striking. Relationships kept appearing.
The lesson was not that relationships somehow override genetics, healthcare, income, exercise, nutrition or disease. They do not. Nor should the Harvard study be treated as universally representative. Its original participants were men living in Boston, and its initial sample was considerably narrower than the populations we would expect from a modern global health study.
Its importance lies partly in how researchers were able to observe human lives over an extraordinary period of time, and relationships kept emerging as part of the story of how well those lives went. More importantly, that finding no longer stands alone.
The evidence became much bigger than Harvard
Psychologist Julianne Holt-Lunstad, now one of the world's leading researchers on social connection and health, has spent much of her career asking a related question. Across much larger populations, how strongly are our social relationships associated with physical health and survival?
One of the landmark answers arrived in 2010. Holt-Lunstad, Timothy Smith and J. Bradley Layton combined 148 studies involving 308,849 participants in a meta-analysis published in PLOS Medicine. Across those studies, people with stronger social relationships had a 50% greater likelihood of survival during the study periods than people with weaker social relationships.
That number needs careful interpretation. It does not mean that having good friends makes an individual person live 50% longer. It means that when researchers pooled evidence across hundreds of thousands of people, stronger social relationships were consistently associated with better survival.
Then came an even larger analysis. In 2023, researchers pooled 90 prospective cohort studies involving 2,205,199 people. Social isolation was associated with a 32% higher risk of death from any cause, while loneliness was associated with a 14% higher risk. Social isolation was also associated with cardiovascular mortality.
The numbers differ between studies because the populations, measurements, statistical methods and definitions differ. But the overall pattern has been difficult to ignore. Across millions of people, social disconnection repeatedly appears alongside poorer health outcomes.
But this does not mean “loneliness kills”
Most of the evidence linking loneliness and physical disease comes from observational research. Researchers observe differences between people who report greater or lesser loneliness or isolation and then follow what happens to their health.
Good observational studies adjust for many factors that might distort the relationship, but they cannot remove every possible explanation. For example, poor health can itself produce isolation. Someone living with chronic pain may leave home less often. Disability can make social participation more difficult. Depression can cause withdrawal. Financial hardship can affect both health and opportunities to socialise. Someone experiencing cognitive decline may gradually lose social contact.
The direction can therefore run both ways. This is known as reverse causation, and it is one of the reasons responsible health journalism should be careful with dramatic claims about loneliness “causing” disease. In fact, some of the newest research is forcing scientists to become even more precise about this.
The newest science is making the picture more complicated and more interesting
In July 2026, researchers published an unusually comprehensive investigation in Nature Communications designed specifically to get closer to the question of causality.
Rather than relying on one research method, they used three different approaches; conventional observational analysis, comparisons between siblings that can help account for shared family and genetic factors, and Mendelian randomisation, a method that uses genetic variants to investigate potentially causal relationships.
The scale was substantial. Depending on the analysis, the researchers used UK Biobank samples ranging from approximately 8,000 to more than 414,000 people, alongside genome-wide association data involving as many as 2.08 million participants.
What they found is important. The researchers found relatively robust evidence that loneliness and social isolation adversely affect mental health and wellbeing, and evidence that loneliness may negatively affect broader measures of general health, including multimorbidity and quality-adjusted life years.
But they did not find convincing evidence that loneliness or social isolation caused the specific physical diseases they examined. The researchers were careful to say that this does not prove there is no physical-health effect; some analyses lacked enough precision to rule one out.
Older observational studies tell us that loneliness and physical disease frequently travel together. The newest causal research asks Is loneliness actually producing those diseases, or are other factors partly responsible for the association?
Right now, the strongest answer is that the relationship with mental health and general wellbeing appears more convincing, while the causal relationship with specific physical diseases remains less certain. That does not weaken the science. It improves it.
Researchers are now looking at what might be happening in the blood
Another fascinating development came in 2025. A Nature Human Behaviour study used data from 42,062 UK Biobank participants to investigate whether social isolation and loneliness were associated with measurable differences in proteins circulating in the blood.
The researchers then followed health outcomes over a median of almost 14 years. During that period, thousands of participants developed cardiovascular disease, dementia, type 2 diabetes, depression or stroke, and more than 4,000 died. The researchers found that some of the proteins associated with social isolation or loneliness were also prospectively associated with later disease and mortality.
This is intriguing because it gives scientists possible biological pathways to investigate.
It does not mean scientists have discovered a “loneliness protein,” nor does it establish a simple chain in which loneliness changes a protein and that protein causes disease. The researchers themselves used additional genetic analyses to investigate causality, and the picture remained complex.
John Cacioppo helped make loneliness a biological question decades earlier
The idea that loneliness might become biologically embedded did not begin with proteomics.
The late psychologist and neuroscientist John Cacioppo was one of the researchers who helped transform the modern science of loneliness. Working with psychologist Louise Hawkley and others, he investigated loneliness as more than an unpleasant emotional state.
Their work proposed that perceived social isolation can increase vigilance for social threats and influence psychological and physiological processes, including stress responses and sleep. One particularly interesting piece of evidence came from a five-year longitudinal study involving middle-aged and older adults in Chicago.
Hawkley, Cacioppo and colleagues found that higher loneliness predicted greater increases in systolic blood pressureover subsequent years, even after accounting for several cardiovascular risk factors and psychological variables. Because participants were followed over time, that tells us more than a study showing simply that lonely people happened to have higher blood pressure at one moment.
It still does not prove loneliness directly caused the increase. But it helped give researchers a reason to investigate how persistent social disconnection might interact with physiological stress.
What about your heart?
Cardiovascular health has become one of the most heavily investigated physical-health areas in loneliness research. A systematic review and meta-analysis led by Nicole Valtorta examined longitudinal evidence on loneliness, social isolation, coronary heart disease and stroke. Across the included datasets, poor social relationships were associated with increased risks of both coronary heart disease and stroke.
Other prospective evidence has produced similar signals. In a study of 119,894 people across 20 high-, middle- and low-income countries, social isolation was associated with greater risks of mortality, stroke and cardiovascular disease. But here again, nuance matters.
A ten-year follow-up study of people already living with cardiovascular disease found that social isolation predicted mortality while loneliness did not after adjustment for established risk factors. That finding reinforces the notion that feeling lonely and objectively having limited social connections are related but different experiences. The cardiovascular evidence is therefore meaningful, but the mechanism is not settled.
Sometimes the relationship between connection and health is surprisingly practical
Not every explanation requires complicated neuroscience or proteins circulating in the blood.
Sometimes another person simply notices. A friend realises you have not been yourself lately. A parent notices that their teenager has stopped eating properly. Someone encourages you to get a symptom checked. A neighbour realises they have not seen an older resident for several days. A sibling takes you to an appointment. Someone helps with the children when you are exhausted. A friend persuades you to come outside for a walk, or somebody brings food when you are ill.
None of those things sounds particularly medical. They can still influence what happens around someone's health. Relationships can provide emotional support, but they can also provide information, practical help, accountability and resources. They can influence whether we exercise, seek care, cope with stress or have somebody available when something goes wrong.
This is one reason Holt-Lunstad has argued that social connection should be understood as a system, rather than as one isolated psychological variable. Our relationships exist inside families, neighbourhoods, workplaces, communities, cultures and economic conditions.
So does our health.
Loneliness and mental health can become a loop
The relationship between loneliness and mental health is particularly important because cause and effect can begin feeding each other. Loneliness can make someone feel low, while feeling low can make reaching out harder. Social anxiety can make connecting with other people difficult, while repeated exclusion can make somebody increasingly anxious about social situations.
A friendship breaks down, someone withdraws, the withdrawal deepens the loneliness, and reaching out becomes even harder. Research involving children and adolescents supports this relationship. A systematic review of 80 studies involving more than 50,000 previously healthy children and adolescents found that social isolation and loneliness were associated with depression and possibly anxiety, both at the time loneliness was measured and years later. Interestingly, the duration of loneliness appeared to matter more than its intensity.
Feeling lonely during a difficult weekend is one thing. Feeling disconnected for months or years is another. Research involving young people who already had mental-health or neurodevelopmental conditions has similarly found associations between loneliness, anxiety and depression, with evidence suggesting that the relationship may operate in both directions.
This means telling a lonely teenager simply to “go and make some friends” can completely miss what is happening. They may be experiencing bullying, depression, anxiety or exclusion. They may have changed schools. They may be neurodivergent and struggling to find relationships in which they feel understood. They may have plenty of friends and still feel unable to tell any of them what is actually going on. The useful question is whether somebody feels lonely. It is why.
New research is following loneliness from childhood into adulthood
That question is becoming even more important as researchers study loneliness earlier in life. A 2026 study using the Environmental Risk Longitudinal Twin Study, a population-representative UK cohort of 2,232 people, examined loneliness and social isolation at ages 12 and 18.
The researchers also tested an interesting theory; perhaps loneliness works partly like hunger, creating an uncomfortable signal that motivates us to reconnect.
In this adolescent cohort, however, loneliness did not appear to protect isolated children by driving successful reconnection. Children who were both isolated and lonely continued to show high levels of isolation later. That matters because young people should not simply be expected to “grow out of” persistent social disconnection. Sometimes they may need help changing the circumstances around it.
The latest meta-analysis asks what loneliness does even in otherwise healthy people
Another recent study tackled an important criticism of loneliness research. Perhaps lonely people appear less healthy simply because illness makes people lonely. Researchers Yixuan Zheng and Pamela Qualter, a psychologist known for her research on loneliness across the lifespan, attempted to reduce that problem by examining studies of otherwise healthy populations.
A large evidence base does not automatically mean every question has been answered.
The Harvard findings help explain why quality matters
After all of this research, it would be easy to conclude that everyone simply needs more people around them. That is not what the evidence says.
This is where the Harvard Study becomes particularly useful again. Waldinger has repeatedly emphasised that the number of relationships is not the only issue. What matters greatly is whether people have relationships they can rely on and whether those relationships are warm and supportive. That is a very different message from telling everyone to become more social.
A teenager does not need to be the most popular person in school. A university student does not need twenty close friends. An adult does not need dinner plans every weekend, and an older person does not need an enormous social network. Someone can know two people and feel deeply connected. Someone else can know hundreds and feel completely alone. The more useful question may therefore be whether there is anyone in your life with whom you feel safe, known and supported.
You can be lonely inside a large family
This matters particularly in cultures where strong family and community networks are sometimes assumed to protect people automatically from loneliness. They can help enormously, but being surrounded by relatives does not guarantee feeling understood.
A teenager can have loving parents and still feel there is nobody they can tell what is actually happening at school. An adult can support an entire extended family and still feel unable to tell anybody that they are struggling. Someone can live in a busy household and have no relationship in which they feel emotionally safe.
You can also occupy many social roles while feeling that nobody really knows you beyond them. You may be somebody's parent, child, guardian, sibling, partner, boss, employee, caregiver or provider and still wonder who you can talk to when you are the one who needs something.
This is precisely why loneliness cannot be measured simply by counting the number of people around someone. Connection also involves trust, support, intimacy and belonging.
Money changes the conditions around loneliness, but it does not eliminate it
Loneliness crosses income levels, but the circumstances surrounding it can be very different.
For someone with limited resources, maintaining a social life can be constrained by transport costs, long working hours, caregiving responsibilities, unsafe neighbourhoods or a lack of accessible public spaces.
A teenager may repeatedly decline outings because they cannot afford them. Someone working several jobs may simply have very little time left for relationships. At the other end of the economic spectrum, money can make social participation easier without guaranteeing intimacy. Someone can travel constantly, attend dinners, belong to exclusive spaces and meet hundreds of people while having very few relationships in which they feel genuinely known.
Money can buy access. It cannot automatically create belonging. That is why telling somebody who feels lonely simply to “put yourself out there” can be remarkably unhelpful.
Sometimes willingness is not the problem. The conditions around connection are.
Moving can disrupt the invisible infrastructure of belonging
You can be excited about moving and lonely at the same time. Someone changes schools. A student leaves home for university. A graduate relocates for work. A family moves cities. Someone emigrates and begins an entirely new life. There may be enormous opportunity in that change, but something else can disappear almost overnight; the ordinary infrastructure of belonging.
The person you used to see after class is no longer there. The neighbour who knew your family is gone. Your usual place of worship is gone. The friend whose house you could visit without planning is now several hours or several countries away. Suddenly, connection requires effort where it once happened automatically.
It can take time to rebuild what proximity used to provide for free. That does not mean the move was a mistake. It means opportunity and loss can coexist.
Social media complicates loneliness rather than simply causing it
The obvious question is whether technology is making us lonelier. The science does not support a satisfying one-word answer. Technology can preserve meaningful relationships that geography would once have weakened. Families can remain closely connected across continents, teenagers can stay friends after changing schools, and people who feel different in their immediate environment can find communities of people with similar experiences online.
A group chat can absolutely be friendship. At the same time, digital life can create an unusual kind of social proximity without closeness. You can know where everyone went, who was invited, what they wore, who is dating whom and who appears to be having the best year of their life while still sitting somewhere feeling completely outside it.
The more useful thought may therefore not be whether social media is inherently good or bad. It may be whether the way you use it helps you participate in relationships or mostly leaves you watching other people's.
Being alone is not the problem
All of this research could easily create another form of wellness anxiety. It would be a mistake to conclude that every quiet evening spent alone is somehow bad for your health.
Solitude and loneliness are not the same thing. Some people naturally need more time alone than others. You can live alone, eat alone, travel alone, spend a quiet weekend by yourself or prefer a smaller social world and still feel deeply connected. Solitude can be restorative. It can create space for reflection, creativity, rest and independence.
Loneliness is different because something feels missing. The goal is therefore not constant company. It is enough meaningful connection for you.
So what actually helps?
This is where the science becomes less neat. There is no universal loneliness solution because there is no universal loneliness. A systematic review of interventions for young people found some promising results but also highlighted small samples, short follow-up periods, differing definitions of loneliness and substantial variation between interventions.
That makes sense because the person who has just changed schools needs something different from the person experiencing depression. Someone who has moved away for university may need to deliberately build routines that involve other people rather than waiting for friendship to happen spontaneously. An older person with limited mobility may need accessible transport or community programmes. A new parent may need practical help before being told to socialise more.
Someone with many acquaintances but very little intimacy may not need another hundred people in their life. They may need to allow one or two people who are already there to know them more honestly. So instead of, “How do I get more people around me?” think, What kind of connection feels missing? The answer may point somewhere completely different.
63° Take
Loneliness is not reserved for older people, people who live alone or people who have no friends. It can happen in a school corridor, a university hall, a busy office, a family home, an expensive restaurant or a group chat that never stops. The science now stretches across decades.
The Harvard Study of Adult Development has followed human lives for more than 80 years and repeatedly found that the quality of our relationships tracks closely with happiness and health across adulthood. Julianne Holt-Lunstad's meta-analytic research has shown across hundreds of thousands, and later millions, of participants that social relationships, loneliness and social isolation are associated with survival.
John Cacioppo and Louise Hawkley's work helped scientists investigate how perceived social disconnection might interact with stress, sleep and cardiovascular physiology. Research involving children and adolescents has found links between persistent loneliness and later depression and anxiety, while new longitudinal evidence is following those relationships from childhood into young adulthood.
And now the science is entering another phase. Researchers are examining thousands of proteins in the blood, using genetic methods, comparing siblings and combining enormous datasets to ask not simply whether loneliness and disease appear together, but why they appear together and whether loneliness itself is actually causing particular health outcomes.
The answer is becoming more nuanced rather than less important. There is strong evidence that loneliness and social isolation are associated with poorer health. There is increasingly persuasive evidence around mental health, wellbeing and broader measures of health. There are plausible biological and behavioural pathways connecting social life with the body. But the newest causal research also tells us to be careful about claiming that loneliness directly causes every physical disease with which it has been associated.
A lonely season does not mean you are damaging your body, and enjoying your own company does not mean you need a larger social life. What the evidence does suggest is that meaningful social connection deserves to sit alongside sleep, movement, nutrition and mental health when we think about the conditions that help human beings live well.
For a teenager, that might mean having one person at school around whom they feel safe. For someone who has moved away from home, it may mean deliberately rebuilding the ordinary routines that place them around other people. For a parent, it might mean asking for enough practical help to have space for relationships beyond caregiving. For someone older, it may mean protecting the people, places and routines that keep them connected to everyday life. For somebody else, the answer may simply be allowing a relationship they already have to become a little more honest.
The important thing is not how many people surround you. It is whether the connection you need is actually reaching you. Being surrounded is not the same thing as belonging, and decades of science increasingly suggest that belonging is not simply pleasant to have. It is part of how human beings live better.
Sources
This article provides general information about social, physical and mental wellbeing and is not a substitute for individual medical or mental-health advice.
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