Fitness and Cognition: A Twin Study

What if exercise could prevent dementia? A growing body of observational (but not interventional) research suggests that physical activity seems to be associated with vigorous cognitive aging. Designing an appropriate, effective study can be challenging. Finding optimal interventions, intervention durations, and duration of effect is difficult. Common genetic and developmental causes often confound results.

Now, researchers at Kings College London, UK, have used the prototypical study design to determine environmental and genetic determinants (the twin study) to examine cognitive aging. The study, published ahead-of-print in Gerontology, is both larger and longer than previous studies that look at similar relationships.

These researcher tested muscle fitness (measured by leg power) in 324 paired healthy female twins aged 43 to 73 years, and identified the weaker and stronger twin in each pair. They followed these women for 10 years. They measured cognitive change and other predictors of cognitive aging, and screened for confounding by factors shared by twins. They also examined differences in brain structure and function after 12 years of follow-up. Factors considered important included heart disease, diabetes, blood pressure, fasting blood glucose, lipids, diet, smoking and alcohol habits, reading IQ, socioeconomic status and birth weight.

Increased leg power at baseline was associated with significantly better cognitive aging. The researchers call this finding "a striking protective relationship."

Increased leg power was also associated with greater grey matter volumes and greater task-related brain activation after 12 years.

This is the first study to link large leg muscular power response to brain changes. One of its strengths is its long duration. Few other studies have look at cognition and fitness for more than 1 year, let alone 10 years.

While the findings connect leg power with cognitive aging and global brain structure, they are silent on whether other fitness measures might do the same. The question that future studies must answer is that of mechanism. Interventions targeted to improve leg power in the long term may help reach a universal goal of healthy cognitive aging.