Losing a partner and living alone can boost a person’s risk of Alzheimer’s disease if they have a particular genetic make-up, a Swedish study has found.

Of the people with a particular gene flaw, those who had split up with or lost a partner before the age of 50 were at the highest risk.

A research team from Sweden’s Karolinska Institute pinpointed the APOE variant 4 gene as the most important genetic risk factor for dementia. The study, published in the online edition of the British Medical Journal, found that living in a relationship with a partner might imply cognitive and social challenges that had a protective effect against cognitive impairment in later life. Dementia is a growing concern amid a globally ageing population, but experts say there are many ways of reducing the risk. Around 25 million people were affected around the world in 2005; by 2040, that number is expected to leap to 81 million. The study looked at 2,000 men and women from eastern Finland aged around 50, and again when they were about 71 years old, screening the groups in advance for the APOE variant 4 gene. Marital status was also recorded. When the team revisited the participants 21 years after the first phase of the study, they found that those who had lived alone in middle age had twice the risk of dementia of those who were living with a partner. However, widows and widowers had three times the risk of those living with a partner. The group with the highest risk of developing Alzheimer’s were those whose partner had died and who remained living alone. The results are thought to be important in the prevention of dementia and cognitive impairment. According to the researchers, led by Krister Hakannson, supportive intervention could be indicated for people who had lost a partner. Experts said the biological effects of widowhood had yet to be proven, and that the link with the APOE gene still needed to be replicated in other studies.