Engaging in high or medium levels of physical activity was associated with slower rates of cognitive decline in people with high or low levels of tau, compared to those with little physical activity. Led by researchers from the Rush University Medical Center, the findings were published in JAMA Network Open on Aug. 11. The researchers noted that measuring levels of tau, a protein that is a hallmark of Alzheimer’s disease, in the blood could help identify people who might benefit from early intervention to slow cognitive decline.
In people living with Alzheimer’s, abnormal accumulation of tau builds up into tangles in the brain. Higher levels of tau are associated with cognitive decline and an increase in memory and thinking problems. Research has shown that physical activity may help slow cognitive decline, but it was unknown if physical activity rates were associated with slow cognitive decline in people who have high levels of tau.
A team of researchers used data from 1,159 older adults who took part in a large study called the Chicago Health and Aging Project (CHAP) between 1993 and 2012. CHAP researchers assessed cognitive function using various tests, asked participants about their physical activity, and collected blood samples from the participants, who did not have Alzheimer’s at the start of the study. In 2019, researchers measured tau concentrations in the blood samples, which had been frozen, and compared rates of cognitive decline among people with high and low tau concentrations and high, medium, and low physical activity levels.
The researchers found that, among participants with high tau concentrations, those who had reported medium levels of physical activity had a 58% slower rate of cognitive decline than participants with low physical activity levels. Those who reported high physical activity levels had a 41% slower rate of cognitive decline than those with low self-reported physical activity levels. For participants with low tau concentrations, those with high physical activity levels had significantly slower cognitive decline than those with medium or low physical activity levels.
The study had some limitations. It included only white and African American participants, and it measured the duration but not the intensity of physical activity. The researchers also note that the rate of cognitive decline was sometimes lower among participants with medium physical activity levels than among those with high physical activity levels; the reasons for this variation warrant further study.
The findings suggest that measuring proteins — such as tau — in the blood could help identify people who would benefit from increased physical activity or other behavior changes that could help slow cognitive decline. Measuring such proteins could also help future studies measure the benefits of behavior changes in people who are at higher risk of Alzheimer’s.
 Tau is a protein that helps stabilize the internal skeleton of nerve cells (neurons) in the brain. This internal skeleton has a tube-like shape through which nutrients and other essential substances travel to reach different parts of the neuron.