People who feel lonely are much more likely than those who do not to develop dementia in old age, according to new research suggesting that loneliness is a risk factor for the condition.

Those who suffer from loneliness have a 64% greater risk of dementia, according to a Dutch study that appears in the Journal of Neurology, Neurosurgery and Psychiatry. But the authors stress that the risk depends on having those feelings and not simply the fact that someone lives alone or is socially isolated.

"Individuals with feelings of loneliness remained 1.64 times more likely to develop clinical dementia than persons who did not feel lonely. In contrast, objective aspects of social isolation no longer showed such an association," concluded the authors of the Amsterdam Study of the Elderly (Amstel), led by Dr Tjalling Jan Holwerda from VU University Medical Centre in Amsterdam.

"These results suggest that feelings of loneliness independently contribute to the risk of dementia in later life. Interestingly, the fact that 'feeling lonely' rather than 'being alone' was associated with dementia onset suggests that it is not the objective situation but, rather, the perceived absence of social attachments that increases the risk of cognitive decline," the authors say.

They studied risk factors for depression, dementia and high death rates among 2,173 Dutch people aged 65 or over who did not have dementia, then examined their health again three years later.

"We hypothesise that feelings of loneliness may ... be considered a manifestation of the deteriorating social skills that are seen as part of the personality change accompanying the process of dementia," they conclude. Feeling lonely can be considered "a major risk factor" for dementia, regardless of whether someone has vascular disease or depression, they add.

But British experts in Alzheimer's reacted cautiously to the study. Dr Simon Ridley, head of research at Alzheimer's Research UK, said someone's age was still the biggest factor in the development of dementia. "But this study links feelings of loneliness to a slightly higher risk of the condition. While such a finding could have important consequences for society, it is hard to determine cause and effect at this stage. Feelings of loneliness could be a consequence of the early stages of dementia rather than a contributing factor."

Jessica Smith, research officer at the Alzheimer's Society, said that while "as this study suggests, feeling lonely could have close links to dementia", more research was needed to ascertain if it was a risk factor or an early symptom of the disease.