A new study suggests that memory, reasoning and comprehension can start to slip as early as age 45.
Understanding cognitive aging might enable early identification of those at risk for dementia.
Over 10 years, starting in 1997, the participants' cognitive function was tested three times.
Researchers noted that, among men aged 45 to 49, reasoning skills declined by nearly 4 percent, and for those aged 65 to 70, those skills dropped by about nearly 10 percent.
For women age 45 to 49 the decline in reasoning was about 5 percent.
The report is published in the current issue of BMJ.