The study, led by Cambridge University, suggests that late-life depression may be linked to dementia because tests for it partially assess apathy.
The research, which was conducted over several years, analysed 450 people with cerebral small vessel disease (SVD) at hospitals in London and the Dutch city of Nijmegen.
Affecting up to one in three elderly people, SVD is the most common cause of vascular dementia, which occurs due to reduced blood flow to the brain.
After accounting for other factors such as age and cognition, scientists found that apathy was connected to a greater risk of developing dementia among the participants, while depression was not.
Jonathan Tay, the lead author from Cambridge’s department of clinical neurosciences, said: “There has been a lot of conflicting research on the association between late-life depression and dementia.
“Our study suggests that may partially be due to common clinical depression scales not distinguishing between depression and apathy.”
Mr Tay added that monitoring apathy could help “to assess changes in dementia risk and inform diagnosis”.
Of those who participated in the study, 20 per cent developed dementia in the UK, while only 11 per cent did in the Netherlands. It is thought the difference between the two cohorts was caused by the more severe burden of SVD across the UK group.
The study, which is published in the Journal of Neurology, Neurosurgery & Psychiatry, is the first of its kind on patients with SVD, according to Cambridge University.
Additional reporting by Press Association