Tests on fruit flies found that those given curcumin, the key chemical in turmeric, lived 75 per cent longer.
The findings, published in the journal PLoS One, could help explain why rates of dementia are lower among the elderly in India than in their Western peers.
Alzheimer’s is linked to the build-up of protein in the brain called amyloid plaques damaging the wiring.
Curcumin did not dissolve the plaque, but accelerated the formation of nerve fibres by reducing the amount of their precursor forms, known as oligomers, from which they were formed.
Prof Per Hammarstrom, of Linkoping University in Sweden, said: “The results confirm our belief that it is the oligomers that are most harmful to the nerve cells.”