A large longitudinal study, comparing physical activity at teenage, age 30, age 50, and late life against cognition of 9,344 women, has revealed that women who are physically active at any point have a lower risk of cognitive impairment in late-life compared to those who are inactive, but teenage physical activity is the most important. When age, education, marital status, diabetes, hypertension, depressive symptoms, smoking, and BMI were accounted for, only teenage physical activity status remained significantly associated with cognitive performance in old age. Although becoming active later in life didn’t make up for being inactive in adolescence, it did significantly reduce the risk of cognitive impairment compared to those who remained physically inactive. The findings are a strong argument for greater effort in increasing physical activity in today's youth.
 . Physical Activity Over the Life Course and Its Association with Cognitive Performance and Impairment in Old Age. Journal of the American Geriatrics Society [Internet]. 2010 ;58(7):1322 - 1326. Available from: http://dx.doi.org/10.1111/j.1532-5415.2010.02903.x