Memory, reasoning and comprehension skills can start to decline at age 45, research published Thursday suggests.

The findings go against previous research that had found cognitive decline starts after age 60 — and highlight the importance of a healthy lifestyle in protecting the brain from dementia, researchers say.

For the study, 5,198 men and 2,192 women aged 45 to 70 were tracked over a 10-year period beginning in 1997 for signs of cognitive decline. Cognitive memory, aural and visual skills and vocabulary were assessed — and participants experienced declines in all areas except vocabulary. Study participants, who were all civil servants, were tested three times during the 10-year period. Educational backgrounds were taken into consideration.

Men aged 45 to 49 experienced a 3.6 per cent decline in mental reasoning and women in the same age group had a decrease of 3.6 per cent. Cognitive memory, aural and visual skills and vocabulary were assessed over a 10-year period — and participants experienced declines in all areas except vocabulary. (iStock)

Men aged 65 to 70 had a mental decline of 9.6 per cent, while women in the same age group had a 7.4 per cent drop.

The researchers said that good cardiovascular health achieved through sensible eating, a healthy body weight and normal blood pressure can help prevent dementia and rapid cognitive decline. They emphasize the value of a healthy lifestyle at a younger age, given the study's findings.

The study was published Thursday in The British Medical Journal.