A review of 21 long-term studies involving over six lakh participants worldwide has found that loneliness is a major risk factor that increases the risk of dementia by over 30 per cent, regardless of age or gender. The study was published in the journal Nature Mental Health.

Loneliness which involves one feeling dissatisfied with their social relationships was also linked with symptoms preceding the stage of being diagnosed with dementia, such as cognitive impairment or decline. Both conditions affect decision-making, memory and thought processes. However, dementia’s symptoms are severe enough to interfere with one’s daily functioning.

The psychological state of feeling disconnected from society is now widely regarded as a risk factor for ill health, even though studies have shown that loneliness cannot directly cause the disease.

Martina Luchetti, an assistant professor at Florida State University, and lead author of the study said, “Dementia is spectrum, with neuropathological changes that start decades before clinical onset. It is important to continue studying the link of loneliness with different cognitive outcomes or symptoms across this spectrum.”

Alzheimer’s Association defines dementia as “Dementia is not a single disease. It's an overall term to describe a collection of symptoms that one may experience if they are living with a variety of diseases, including Alzheimer's disease. Diseases grouped under the general term "dementia" are caused by abnormal brain changes. Dementia symptoms trigger a decline in thinking skills, also known as cognitive abilities, severe enough to impair daily life and independent function.”

Aspects of psychological well-being such as lacking purpose in life or feeling like there are fewer opportunities for personal growth were found to have noticeably declined three to six years before a diagnosis of mild cognitive impairment.

The study found that loneliness increased the overall risk of dementia by 30 per cent, the risk of Alzheimer’s disease by 39 per cent, vascular dementia by 73 per cent and cognitive impairment by 15 per cent.

Alzheimer’s disease is caused by the accumulation of proteins in the brain, which is thought to cause cell death, while vascular dementia is caused by damage to brain’s blood vessels.

Luchetti said that the findings can help identify sources of loneliness to support the well-being and cognitive health of ageing adults. The authors acknowledged that the study included subjects largely from the the western world. They called for future research to look at data from other countries, including low-income ones, where cases of ageing-related conditions are rising. Luchetti added, “We know there are rising cases of dementia in low-income countries. Future studies need to gather more data from those countries to evaluate what are the effects of loneliness in different national and cultural contexts.”

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