Being physically active throughout life appears to lower the risk of dementia in old age, and the earlier in life that exercise happens, the better, new research suggests.

The study found that rates of cognitive impairment was significantly lower in women aged 65 and older who reported they were physically active as teens, compared to those who remembered being inactive in their teen years.

Dr. Laura Middleton, the principal investigator and postdoctoral fellow at the Heart and Stroke Foundation Centre for Stroke Recovery at Sunnybrook Health Sciences Centre in Toronto, notes there is growing evidence that physical activity is one of the most promising ways to prevent dementia.

"This research provides evidence that physical activity earlier in life may be important to reducing the risk of cognitive impairment in late life," she said in a news release.

"These results not only confirm that promoting physical activity is among the most promising strategies in the prevention of dementia in old age, but also stress that health promotion interventions targeting people earlier in life may be particularly important."

Middleton worked on the project while she was at the University of California in San Francisco, and used data from the Study of Osteoporotic Fractures. She analyzed data from 9,704 women in four U.S. cities who were aged 65 or older.

The volunteer described their participation in regular physical activity as teens, at ages 30 and 50, and in late life. Their cognition skills were then evaluated using a short, standardized test. Those who performed well below the average were classified as cognitively impaired.

Middleton's team found that people who were active ast teenagers had a lower risk of cognitive impairment compared to any of the other ages.

  • For those who were active in their teen years, the prevalence of cognitive impairment at age 65 or older was 8.5 per cent, compared to 16.7 per cent among those who weren't physically active as teens.
  • For those active versus inactive at age 30, prevalence of cognitive impairment was 8.9 per cent compared to 12 per cent
  • For those who got active at age 50, the rate was 8.5 per cent versus 13.1 per cent

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

While the numbers suggested being active at younger ages was most important, even women who were inactive as teenagers but who became active at 30 or 50 had a lower risk of cognitive impairment than those who stayed inactive most their lives.

The study will appear in the July issue of the Journal of the American Geriatrics Society. The data were already presented at the American Association of Neurology conference in 2010 and the Canadian Dementia Conference in 2009.

The study was limited in that it was a retrospective study that asked volunteers to remember their activity levels decades before. As well, many of the volunteers went on to develop dementia, which may have affected the answers they gave.

As well, the study was observational and so can't prove cause and effect between physical activity and decreased risk of cognitive impairment,

Still, Middleton thinks there are some possible mechanisms might explain the association between fitness and dementia. For example, exercise could have a positive effect on brain plasticity. It could also improve vascular health, which could reduce the risk of cognitive impairment.

Middleton says her results suggest that with low physical activity levels in today's youth could mean increased dementia rates in the future. That suggests that dementia prevention programs should encourage physical activity in younger people -- not just in mid and late life.