Mental ability can start to falter from age of 45 and onwards, not from age of 60 as previously thought, according to research published by the British Medical Journal (BMJ).
Cognitive function was measured three times over 10 years to assess memory, vocabulary, hearing and visual comprehension skills.
All cognitive scores, except vocabulary, declined among all age groups during the study, and there was evidence of faster decline among older people.
Researchers from the Center for Research in Epidemiology and Population Health in France and University College London observed 5,198 men and 2,192 women over a 10-year period from 1997.
The volunteers were civil servants aged between 45 and 70 who had been enrolled in a long-term health study.
In men, there was a 3.6 percent drop in reasoning after 10 years among those who were aged 45 to 49 at the start of the study and 9.6 percent among those aged 65 to 70.
In women, the decline was 3.6 percent and 7.4 percent in the same age groups respectively.
“Cognitive decline is already evident in middle age,” says the paper, which defines this as the years from 45 to 49.
Authors of the study have said, diseases such as dementia were now thought to be the result of long-term changes over at least 20 to 30 years.
There is enough evidence already to show the importance of healthy lifestyles and good heart health in impacting on the later risk of dementia.
The findings should spur further research into spotting and braking cognitive deterioration, the authors hope.
Many societies face an ‘exponential increase’ in the number of elderly people as a result of increases in life expectancy, they note.