REVIEW OF: Desai P et al, JAMA Netw Open 2021;4(8):e2120398

STUDY TYPE: Population-based cohort study

Does exercise prevent—or at least slow down—dementia? It’s a tantalizing but still unanswered question. Many studies have shown a correlation between physical activity and better cognitive functioning, but correlation does not equal causation. Higher cognitive capacity could just as easily encourage people to be more physically active, or cognitive impairment could result in a reduced ability to exercise.

The latest study to weigh in on this issue still doesn’t help us with the causality question—but it did measure biomarkers in addition to mental status, which adds “harder” data to the exercise-cognition connection. This study measured blood levels of tau, as high levels of tau have been associated with cognitive decline and progression from mild cognitive impairment to Alzheimer’s disease.

Researchers used data from 1,159 older adults who participated in the Chicago Health and Aging Project between 1993 and 2012. Participants were Black and White, and older than 65 years without Alzheimer’s at study entry. Participants were included if they had a baseline blood sample measuring total serum tau concentrations and at least two cognitive assessments. The average age of participants was 77 years old, and they were predominantly female (63%) and Black (60%) with a mean educational level of 12.6 years. Participants were divided into three groups by self-reported duration of physical activity: little (no exercise), medium (<150 minutes/week), and high (>150 minutes/week). Cognitive function was measured by the East Boston Memory Test, the Symbol Digit Modalities Test, and the Mini Mental State Examination.

All results were adjusted for demographic factors, including baseline APOE4 status and chronic medical conditions. Participants with high total tau at baseline had a slower rate of cognitive decline if they reported high or medium physical activity compared to those who reported no exercise. Participants with low tau levels experienced a smaller benefit in the rate of cognitive decline, although those with high physical activity levels still had a statistically significant slower cognitive decline than their sedentary counterparts.

Drawbacks of this study include limited generalizability, as the study only included White and Black participants. Information on participants’ physical activity levels lacked details on type and intensity, and self-reporting can introduce bias into the data.

Carlat Take

This study suggests that staying physically active in old age may slow cognitive decline, especially in older adults with biomarkers of neurodegeneration. We should encourage physical activity in our older patients, as moderate to high physical activity improves brain health.