According to Swedish researchers the single life can increase some people's dementia risk
The researchers from the Karolinska Institute suggest that people who have a particular gene variation and live alone in middle-age, have a higher risk of developing dementia.
The researchers say the APOE variant 4 is the most important genetic risk factor for Alzheimer's and particularly affects those who split up or were widowed from their long-term partner before the age of 50.
As the world's aging population increases, dementia has become a growing concern - in 2005 around 25 million people had dementia, but the number is expected reach 81 million by 2040.
The researchers studied 2,000 men and women from eastern Finland aged around 50 - they looked at their marital status and also carried out genetic tests to see if they carried the gene APOE variant 4 and looked at them again 21 years later.
They found that people living alone in middle-age had twice the risk of dementia than those who were living with a partner - widows and widowers had three times the risk of dementia - but those with the APOE gene variant who had lost their partners and remained alone had the highest risk of all of developing Alzheimer's.
The team, led by Dr Krister Hakannson, say the results are important for preventing dementia and cognitive impairment and she suggest s that supportive intervention could be helpful for people who have lost a partner.
They say living in a relationship with a partner might imply cognitive and social challenges that have a protective effect against cognitive impairment in later life and the link with the APOE gene variant warrants further study but is supported by previous research.