Regular exercise reduces risk of dementia and Alzheimer’s disease
http://bmj.bmjjournals.com/cgi/content/full/332/7534/137-a/DC1
London

Susan Mayor

More evidence for the "use it or lose it" approach to ageing has come from
a study published this week showing that older adults who exercised three
or more times a week had a significantly lower risk of developing dementia
than adults who exercised less (Annals of Internal Medicine 2006;144:73-81).

The study included a randomly selected group of 1740 adults aged 65 years
or older with normal cognitive function, as assessed by the Cognitive
Ability Screening Instrument, at baseline. Participants were examined to
identify incident dementia every two years at the same time as they
reported their exercise patterns. A session of exercise was defined as at
least 15 minutes of physical activity at any one time, including walking,
hiking, aerobics, callisthenics, swimming, water aerobics, weight training,
and stretching.

In a mean follow-up of 6.2 years, 158 people developed dementia, and, of
these, 107 were diagnosed as having Alzheimer’s disease. The incidence of
dementia was 13.0 per 1000 person years for people who exercised at least
three times a week, compared with 19.7 per 1000 person years for people who
exercised less often. This meant that the risk of developing dementia was
38% lower in the regular exercise group, with an age and sex adjusted
hazard ratio of 0.62 (95% confidence interval 0.44 to 0.86; P=0.004). The
risk reduction associated with exercise was greater in people with lower
performance levels at baseline, than in those with higher performance at
baseline, who continued to exercise.

Eric Larson, director of the Center for Health Studies at Group Health
Cooperative, a health maintenance organisation in Seattle, and lead author
of the study, said, "This is the most definitive study yet of the
relationship between exercise and risk for dementia. Previous research on
this relationship has yielded mixed results. We learnt that a modest amount
of exercise would reduce a person’s risk of dementia by about 40%. That’s a
significant reduction.

"The group that benefited the most were the people who were frailest at the
start of the study. So this means that older people really should ‘use it
even after you start to lose it,’ because exercise may slow the progression
of age related problems in thinking."

In an accompanying editorial, Laura Podewils, from the Centers for Disease
Control and Prevention in Atlanta, and Eliseo Guallar, from the Johns
Hopkins Bloomberg School of Public Health in Baltimore, said that the study
provided important evidence of the value of physical exercise in reducing
the risk of dementia (pp 135-6). But they called for further research to
determine whether physical activity is causally associated with a lower
rate of dementia or whether it is a proxy for "life engagement"—other
lifestyle or sociodemographic characteristics associated with the
development of dementia. Research is also needed to determine the type,
frequency, intensity, and duration of physical activity that is most
beneficial in preventing cognitive deterioration, they concluded.