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Physical exercise showed a more pronounced effect on cognitive reserve in women than in men, an observational study showed.

Higher levels of physical activity were associated with greater processing speed reserve in older women (β=0.04, 95% CI 0-0.08) but not in older men (β=0.004, 95% CI -0.04 to 0.05), reported Judy Pa, PhD, of the University of California San Diego, and co-authors.

For both sexes, cognitive activities -- reading, taking classes, or playing games -- were associated with greater processing speed reserve (β=0.13, 95% CI 0.05-0.21), the researchers noted in .

Greater physical activity was not associated with memory reserve in either sex. More cognitive activities showed a trend toward greater memory reserve in women (β=0.06, 95% CI -0.02 to 0.14), but not in men.

Cognitive reserve -- the ability to preserve cognition despite brain pathology -- may help slow dementia.

Recent research has shown that among people in their 80s, a cognitively active lifestyle that involves reading and processing information may delay the onset of dementia in Alzheimer's disease by as much as 5 years. Other studies have pointed to cognitive reserve as one reason some centenarians show resilience to cognitive decline, despite brain pathology.

Pa and colleagues evaluated older adults who were part of the Washington Heights/Inwood Columbia Aging Project (), a study conducted in New York City in three waves starting in 1992, 1999, and 2009. Of 758 total participants, 292 were Black, 224 were Hispanic, and 242 were white.

The mean age of the cohort was 76, and 62% were women. Overall, 449 people were cognitively normal, 242 had mild cognitive impairment, and 67 had dementia. Of the entire group, 28% carried an APOE4 gene.

Self-reported physical activity was assessed using the Godin Leisure-Time Exercise questionnaire, converted to metabolic equivalents (). Self-reported cognitive activity was calculated as the sum of three yes/no questions about reading, taking classes, or playing games. Participants were given one point for each type of cognitive activity, for a maximum of three points.

Cognitive reserve scores were calculated by analyzing hippocampal volume, total gray matter volume, white matter hyperintensity volume, and composite cognitive scores for processing speed and memory.

Average METS were 6.12 and the mean cognitive activity score was 1.42. Participants engaged in an average of at least 15 minutes a week of activity that elevated their heart rate, like brisk walking, the researchers said.

"Based on the effect sizes observed for physical activity (METS) and age, a two-fold increase in physical activity would be equivalent to an estimated 2.75 fewer years of processing speed aging in women," Pa and co-authors observed.

"Each additional cognitive activity corresponded to 13 fewer years of processing speed aging (10 years among women, 17 years among men)," the team added.

Among women only, APOE4 status attenuated relationships between METS and processing speed reserve (β=-0.09, 95% CI -0.22 to 0.04), and between cognitive activities and both processing speed reserve (β=-0.26, 95% CI -0.63 to 0.11) and memory reserve (β=-0.20, 95% CI -0.50 to 0.093).

Future studies are needed to test whether lifestyle activities have causal relationships with cognitive reserve and whether causality may be modified by sex and APOE4, Pa and colleagues noted.

The study is limited by its reliance on self-reported cognitive and physical activity, which was subject to recall bias or errors made by participants who had cognitive impairment. However, the associations found in the study were seen in people both with and without impairment, the researchers pointed out. Reverse causation may have influenced the results and the findings may not apply to people outside New York City or similar urban areas. In addition, other factors related to cognitive reserve, such as education, were not assessed.

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