Women who are physically active have a lower risk of cognitive impairment in late-life, compared to those who are inactive.

A study of more than 9,000 women, published in the Journal of the American Geriatrics Society, also found that teenage physical activity appears to be most important to avoid dementia and more minor forms of cognitive impairment in old age.

A research team, led by Laura Middleton of Sunnybrook Health Sciences Centre, Canada, compared the physical activity at teenage, age 30, age 50, and late life against cognition of 9,344 women from Maryland, Minnesota, Oregon and Pennsylvania to investigate the effectiveness of activity at different life stages.

Of the participants, 15.5 per cent, 29.7 per cent, 28.1 per cent, and 21.1 per cent reported being physically inactive at teenage, at 30 years, at 50 years, and in late life respectively; the increase in cognitive impairment for those who were inactive was between 50 per cent and 100 per cent at each time point.

When physical activity measures for all four ages were entered into a single model and adjusted for variables such as age, education, marital status, diabetes, hypertension, depressive symptoms, smoking, and BMI, only teenage physical activity status remained significantly associated with cognitive performance in old age.

"Our study shows that women who are regularly physically active at any age have lower risk of cognitive impairment than those who are inactive but that being physically active at teenage is most important in preventing cognitive impairment," said Middleton.

The researchers also found that women who were physically inactive at teenage but became physically active at age 30 and age 50 had significantly reduced odds of cognitive impairment relative to those who remained physically inactive. In contrast, being physically active at age 30 and age 50 was not significantly associated with rates of cognitive impairment in those women who were already physically active at teenage.