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Conventional risk factors largely explain links between loneliness and first-time heart disease or stroke, but social isolation is still associated with death among those with pre-existing cardiovascular disease, according to the largest study of its kind, published in Heart. Researchers from the University of Helsinki analysed data for nearly 480 000 people aged 40–69 years who were part of the UK Biobank study between 2007 and 2010. Participants provided detailed information about their ethnic background, educational attainment, household income, lifestyle (smoking, drinking, exercise), and depressive symptoms. They were also asked a series of questions to gauge their levels of social isolation and loneliness. Height, weight, and grip strength were measured, and blood samples collected. Their health was then tracked for an average of 7 years. Nine percent of respondents were deemed to be socially isolated, 6% lonely, and 1% both. Those who were socially isolated or lonely were more likely to have long term medical conditions and to be smokers, while those who were lonely reported more depressive symptoms. Social isolation was associated with a 43% higher risk of first-time heart attack, after adjusting for age, sex, and ethnic background. But behavioural, psychological, health, and socio-economic factors accounted for most (84%) of the increased risk, and the initial association with social isolation was no longer statistically significant. Similarly, social isolation was initially associated with a 39% increased risk of a first-time stroke, but the other conventional risk factors accounted for 83% of this risk. Similar results were obtained for loneliness and risk of first-time heart attack or stroke. But this was not the case for those with pre-existing cardiovascular disease, among whom social isolation was initially associated with a 50% higher risk of death, and was still 25% higher after adjusting for the other known factors. Similarly, social isolation was associated with a 32% increased risk of death after adjusting for all the other conventional factors.