Researchers conducted an interview for 2,000 people with average age of 50.4 years, selected randomly in the Kuopio and Joensuu regions of eastern Finland in the 1970s and 80s.

Out of all, 1,409 volunteers were then re-examined when their age was between 65-79 years in 1998 for cognitive impairment.

Total 57 volunteers were diagnosed with Alzheimer’s disease or other forms of dementia; 82 suffered from mild cognitive impairment; the remaining 1,270 were healthy though.

People living without a partner at mid-life had around twice the risk of developing cognitive impairment in later life compared with people living with a partner, the study found.

People who were widowed or divorced in mid-life and who were not living in partnership in later life were at almost thrice the risk.

Variables that are known to affect cognitive impairment like education, smoking habits and others were all taken into account.

The investigators found that the difference was more between men and women.

In men who lived alone in mid-life, the cognitive impairment later in life was 2.5 times more compared to co-habitants, and in women the risk was 1.87 times.

The researchers identified a major association of Alzheimer’s, living alone and a variant of a gene called apolipoprotein E-e4 which makes a protein associated with this disorder.

Living with a partner might imply cognitive and social challenges that help shield against dementia, but why this could be so has to be explained, the authors say.