Late-life depression could become a major risk factor for developing Alzheimer's faster than others, a study says.

Depression in the elderly could point to a build up of a naturally occurring protein in the brain called beta-amyloid, a hallmark of Alzheimer's disease. 

"Our results clearly indicate that mild cognitively impaired subjects with depressive symptoms suffer from elevated amyloid-levels when compared with non-depressed individuals," said Axel Rominger from University of Munich in Germany.

The combination of elevated amyloid-levels and coexisting depressive symptoms constitute a patient population with a high risk for faster progression to Alzheimer's disease, Rominger added. 

The study involved 371 patients with mild cognitive impairment who underwent PET (Positron emission tomography) imaging with the radiotracer F-18 florbetapir and magnetic resonance imaging (MRI) chosen retrospectively from a global dementia imaging database. 

Alzheimer's disease, the most prevalent form of dementia, is a currently incurable neurodegenerative disease with marked protein aggregates including beta-amyloid and tau.

The disease begins developing years before noticeable cognitive decline and memory loss.It is estimated that 44.4 million people are living with dementia worldwide.