Among individuals with high tau levels, undertaking physical activity led to a much lower decline in cognitive function over time.
Tau is a microtubule-associated protein in neurons but aberrant assembly of the protein is present in neurodegenerative disorders. However, while abnormalities in the assembly of tau appear to be strongly associated with the development of disorders such as dementia and Alzheimer’s disease, it remains unclear how this links with upstream events. Tau levels can now be measured in blood and higher levels have been associated with cognitive decline and with the development of Alzheimer’s disease. Increased physical exercise improves blood flow to the brain and greater levels of activity appear to be associated with a reduced risk of developing degenerative conditions such as Alzheimer’s disease. Given that tau levels can serve as a biomarker of cognitive decline what remains uncertain is whether it is possible to correlate changes cognition with preventative strategies such as physical exercise over time. This was the aim of a study by a team from the Rush Institute for Healthy Aging, Rush University, Chicago, US. They used data contained within the Chicago Health and Aging Project (CHAP), which is a population-based cohort of African Americans and White participants, 65 years and older. The CHAP study is designed to explore chronic common health problems, especially risk factors for incident Alzheimer’s disease.
For the present study, the researchers included participants older than 65 years and without Alzheimer’s disease at baseline. Samples of tau were measured between 1994 and 2012 and frozen and later assayed. The team collected information on the levels of physical activity of participants and categorised this as either low, medium and high. Medium activity was where it was for less than 150 minutes per week, or high, if greater than 150 minutes. Low levels indicated that participants did not undertake any physical activity. Tau blood levels were also measured and considered as either high (> 0.40 pg/ml) or low (<0.40 pg/ml) based on earlier data suggesting a higher rate of cognitive decline in those with levels greater than 0.40. The main outcome of the study was global cognitive function based on a battery of tests and the measurement duration for the study was 18 years.
Findings
A total of 1159 participants were included with a mean age of 77.4 years (63% female) and with 60% of African American descent. In participants with a high tau level (> 0.40 pg/ml) and a medium level of physical activity, there was a 58% slower rate of cognitive decline per year compared to those undertaking little physical activity. Similarly, in those with high tau levels and high physical activity, the rate of cognitive decline was 41% slower than those with low activity. Even where tau levels were low, medium physical activity was associated with a 2% slower rate of decline and a 27% lower rate for those with high physical activity.
The authors concluded that physical activity was associated with a much slower decline in cognitive function among those with both low and high tau levels and that this could be easily measured with tau levels. They called for future studies to examine the relationship between tau levels and other forms (i.e., strength training) of physical activity.
Citation
Desai P et al. Longitudinal Association of Total Tau Concentrations and Physical Activity with Cognitive Decline in a Population Sample. JAMA Netw Open 2021
