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New observational data add one more reason to strive for a healthy middle age. Researchers led by Helena Hörder, University of Gothenburg, Sweden, report that women who scored high on a fitness test in midlife were nearly 90 percent less likely than their moderately fit or unfit peers to develop dementia decades later. Also, the fittest women held dementia at bay 10 years longer. The study, now available online, appears in the April 10 Neurology.

“This is a very important study because of the extremely long follow-up,” said Prashanthi Vemuri, Mayo Clinic in Rochester, Minnesota. Miia Kivipelto, National Institute for Health and Welfare, Helsinki, also valued the report. “Together with previous studies, it supports the idea that what is good for the heart is also good for the brain,” she said. Both cautioned, however, that the sample size was small.

Several observational studies have suggested physical activity lowers the risk of dementia, and a handful of clinical trials testing the effects of lifestyle interventions, including exercise, support this proposal (e.g., Norton et al., 2014; Blondell et al., 2014; Nov 2015 conference news). Compiling data from many studies, a commission convened by The Lancet attributed physical inactivity late in life to a 3 percent increase in dementia risk (Livingston et al., 2017).

To gain a long-term view of the link between physical fitness and brain health, Hörder mined data from the Prospective Population Study of Women. This tracked the health of 1,462 middle-aged Swedish women beginning in 1968. Hörder analyzed data from a subgroup of 191 women who were 38–60 years old at that time. She focused specifically on fitness, which is determined by both physical activity and genetic factors. At baseline, the women rode stationary bikes fitted with ergometers that measured their work output. First, they pedaled easy for six minutes, producing 32 and then 64 watts.

fast walk is equivalent to about 100 watts. After a five-minute break, the women began pedaling again, but this time, based on their performance on the first test, the resistance was adjusted to measure their peak workload. Participants pedaled as hard as they could at this load until they felt exhausted and had to stop, typically after about six minutes.…