Want to help ward off Alzheimer’s in old age? It may never be too early to start exercising.

A new study of more than 9,000 women suggests that remaining physically active throughout your life helps keep memory and thinking skills sharp and ward off Alzheimer’s in old age. Women who were physically active during their teenage years appeared to get the greatest boost in brain health. The findings were published in the Journal of the American Geriatric Society.

Researchers analyzed medical data from 9,395 women ages 65 and over who were part of a study on bone health. They were asked about their exercise and physical activity levels at ages 30, 50 and later. They were also given tests of memory function to look for signs of Alzheimer’s disease.

Women who were most active throughout their lifetimes appeared to be at lower risk of developing Alzheimer’s and other forms of dementia. Those who were active as teenagers seemed to be least likely to have cognitive problems as seniors.

Fewer than one in 11, or 8.5 percent, of the women who reported being physically active as teenagers developed Alzheimer’s or other types of dementia as seniors. In contrast, about one in six women, or 16.7 percent, who had not been active as teens had developed dementia.

The findings confirm what others have shown: that getting regular exercise helps keep the mind sharp. Earlier this year, two studies reported that resistance training, in which the body works against weight, may have particular benefits for the brain. And ongoing physical activity has been linked to a longer life and all kinds of benefits for the body, including less heart disease, fewer falls and broken bones, greater lung function and a trimmer physique.

It may be especially important to exercise and adopt other healthy lifestyle measures early in life. Mounting evidence suggests that Alzheimer’s risk can be cut by exercise in the middle years. And these findings suggest that the earlier you start, the better.

Alzheimer’s is a complex disease that depends on genes and many factors. Exercise is likely just one part of the preventive puzzle.

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by William J. Netzer, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.

Source: Laura E. Middleton, Deborah E. Barnes, Li-Yung Lui, Kristine Yaffe: “Physical Activity Over the Life Course and Its Association with Cognitive Performance and Impairment in Old Age.” Journal of the American Geriatric Society, July 2010, pages 1322-1326.