High cardiorespiratory fitness linked to lower risk of dementia

High cardiorespiratory fitness is associated with better cognitive performance and lower risk of dementia in the long term, including in people with a genetic predisposition to dementia, show the findings of a study published online in the British Journal of Sports Medicine.

Cardiorespiratory fitness (CRF) is the capacity of the circulatory and respiratory systems to supply oxygen to muscles and declines increasingly with age as skeletal muscle is lost.

CRF declines by around 3–6% per decade when people are in their 20s and 30s, but this accelerates to more than 20% per decade by the time people reach their 70s. Low CRF is a strong predictor of cardiovascular events such as strokes and heart attacks and mortality from all causes.

Most previous studies investigating the impact of CRF on cognitive function and dementia risk included a small number of participants. For this study, the authors looked at a much larger group by accessing data on 61,214 dementia-free people aged 39–70 years who enrolled in the UK Biobank study between 2009 and 2010 and were followed for up to 12 years.

At enrollment, a six-minute submaximal exercise test on a stationary bike was completed to estimate CRF, cognitive function was estimated using neuropsychological tests, and genetic predisposition for dementia was estimated using the polygenic risk score for Alzheimer’s disease. During the follow-up period of up to 12 years, 553 people (0.9%) received a diagnosis of dementia.

Participants were divided into three equal-sized groups standardized by age and sex according to their CRF scores for the analysis, which showed that people with high CRF had higher cognitive function and a lower risk of dementia.

Compared with people with low CRF, the incidence rate ratio (IRR) of all dementia was 0.6 for people with high CRF, and onset of dementia was delayed by 1.48 years. A high CRF also reduced all dementia risk by 35% among people with a moderate/high polygenic risk score.

This is an observational study, and as such, can’t establish cause and effect, and the researchers acknowledge various imitations to their findings.

Most importantly, the number of dementia cases may have been underestimated because UK Biobank participants are generally healthier than the general population, plus individuals with certain health conditions were excluded from the exercise test making the population investigated “healthier” still.

The reliance on registries to identify dementia cases might have led to a further underestimation. Also, the submaximal exercise test used is considered less accurate than maximal exercise testing which requires participants to exercise to exhaustion, and any association between CRF change and dementia risk could not be examined due to the lack of repeat CRF measurements.

The authors conclude, “Our study shows that higher CRF is associated with better cognitive function and decreased dementia risk. Moreover, high CRF may buffer the impact of genetic risk of all dementia by 35%.”

They add that their findings suggest that, “Enhancing CRF could be a strategy for the prevention of dementia, even among people with a high genetic predisposition for Alzheimer’s disease.”

Further research on the relationship between CRF and brain health, especially in older adults, and on the mechanisms by which CRF modifies the relationship between genetic risk and dementia is needed, they say.