People over 50 who suffer from negative emotions and disruption when they lose their partners have the highest risk of developing Alzheimer’s disease, according to a study published in the British Medical Journal.

Being widowed or divorced in mid-life carries three times the risk, while singles have double the risk of getting dementia than people who are married or cohabiting, according to a study from researchers in Sweden and Finland.

“Supportive intervention for individuals who have lost a partner might be a promising strategy in preventive health care,” lead researcher Krister Hakansson from Vaxjo University and the Karolinska Institute in Stockholm wrote in the study.

The number of dementia sufferers is forecast to increase to more than 80 million in 2040 from about 25 million in 2005, the researchers wrote. Higher education levels, physical exercise, mentally demanding work, top jobs and leisure and intellectual activities have been shown to protect against dementia, they said.

The researchers followed 1,449 people aged 65 to 79 years living in the Kuopio and Joensuu regions in eastern Finland for an average of 21 years to see whether their marital status affected the development of dementia later in life.

The dementia and Alzheimer’s disease risk increased if people lost their partners or got divorced, Hakansson found. The highest risk occurred in people who lost their partners or got divorced and also had a known genetic risk factor that’s associated with the development of Alzheimer’s disease.

These results add to a growing body of evidence that social factors may help sustain healthy brain functioning, Hakansson said. The development of cognitive impairment and dementia is a long process that’s affected by various factors throughout life, epidemiologist Catherine Helmer said in an editorial.

Research should now focus on the stress caused by separation and satisfaction with relationships, Helmer said. “Unmarried, especially widowed, people could then be targeted for preventive strategies that encourage them to increase their social engagement by taking part in cultural, social and sporting activities.”

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