Researchers studied nearly 7,400 British people for a decade and
for those aged 45-49, it was discovered their ability to reason
declined 3.6 percent in the time they were studied. The decline
sped up for people aged 65-70: men experienced a 9.6 percent
decline in ability to reason, and a 7.4 percent decline for
women. Other mental abilities that faded included memory, and
so-called verbal fluency, which measures a person's ability to
quickly say words in a particular category. However, people's
vocabulary didn't change.The BMJ report says that it was
previously widely accepted that cognitive decline did not occur
until age 60. The researchers say that with increasing life
expectancy, understanding cognitive aging will be a challenge of
this century.