This article in the New York Times has some interesting points about the value of staying in the workforce later in life. The earlier someone retires, the worse they tend to do on laboratory tests of memory.
Retirement, however, doesn’t need to mean a lack of engagement in life, or a loss of cognitive stimulation – though it’s a convenient stand-in for those variables in this research study. More interesting would be if the researchers examined the day-to-day activities of the study participants for more than just if they engaged in paid employment. Volunteer work, participation in clubs and other groups, and continued engagement in a vibrant cognitive and social life are all likely to be correlated with better cognitive performance – whether or not they involve paid employment.