They warned this could lead to a sharp increase in dementia rates, reversing recent improvements. Professor Hui Zheng, a sociologist at Ohio State University, said: “It’s shocking to see this decline in cognitive functioning among baby boomers after generations of increases in tests.
“But what was most surprising to me is this decline is seen in all groups – men and women, across all races and ethnicities and across all education, income and wealth levels.”
People with worse cognitive scores in their 50s and 60s are at higher risk of developing dementia later.
The US study analysed data from more than 30,000 Americans surveyed every two years for almost twenty years.
They had to recall words heard earlier, count down from 100 by sevens, name objects they were shown and perform other tasks.
Average scores increased from generation to generation – peaking among war babies of 1942 to 1947.
Professor Zheng said: “Baby boomers already start having lower cognition scores than earlier generations at age 50 to 54.”
The biggest factors thought to drive the difference were lower wealth, higher levels of loneliness and depression, lack of physical activity and obesity.
Others were living without a spouse, being married more than once, having psychiatric problems and cardiovascular conditions.
In the UK there are about 850,000 people with dementia – a figure set to rise to two million by 2050.