It is well established that exercise and physical fitness correlate well with reduced incidence of all of the common age-related diseases, and reduced mortality risk. It is hard to establish causation from the contents of human epidemiological databases, but the analogous animal studies convincingly demonstrate that exercise improves health. There is no reason to expect humans to be all that different in this matter. Here, researchers show that, much as expected, greater fitness correlates with reduced risk of dementia. Of note, patients that improved their fitness over the years of later life exhibited reduced disease risk and improved life expectancy.
Cardiorespiratory fitness is associated with risk of dementia, but whether temporal changes in cardiorespiratory fitness influence the risk of dementia incidence and mortality is still unknown. We aimed to study whether change in estimated cardiorespiratory fitness over time is associated with change in risk of incident dementia, dementia-related mortality, time of onset dementia, and longevity after diagnosis in healthy men and women at baseline. We linked data from the prospective Nord-Trøndelag Health Study (HUNT) with dementia data from the Health and Memory Study and cause of death registries (n=30,375). Included participants were apparently healthy individuals for whom data were available on estimated cardiorespiratory fitness and important confounding factors.
Cardiorespiratory fitness was estimated on two occasions 10 years apart, during HUNT1 (1984-86) and HUNT2 (1995-97). HUNT2 was used as the baseline for follow-up. Participants were classified into two sex-specific estimated cardiorespiratory fitness groups according to their age (10-year categories): unfit (least fit 20% of participants) and fit (most fit 80% of participants). To assess the association between change in estimated cardiorespiratory fitness and dementia, we used four categories of change: unfit at both HUNT1 and HUNT2, unfit at HUNT1 and fit at HUNT2, fit at HUNT1 and unfit at HUNT2, fit at both HUNT1 and HUNT2. Using Cox proportional hazard analyses, we estimated adjusted hazard ratios (AHR) for dementia incidence and mortality related to temporal changes in estimated cardiorespiratory fitness.
During a median follow-up of 19.6 years for mortality, and 7.6 years for incidence, there were 814 dementia-related deaths, and 320 incident dementia cases. Compared with participants who were unfit at both assessments, participants who sustained high estimated cardiorespiratory fitness had a reduced risk of incident dementia (AHR 0.60) and a reduced risk of dementia mortality (AHR 0.56). Participants who had an increased estimated cardiorespiratory fitness over time had a reduced risk of incident dementia (adjusted hazard ratio 0.52) and dementia mortality (adjusted hazard ratio 0.72) when compared with those who remained unfit at both assessments. Each metabolic equivalent of task increase in estimated cardiorespiratory fitness was associated with a risk reduction of incident dementia (AHR 0.84) and dementia mortality (AHR 0.90). Participants who increased their estimated cardiorespiratory fitness over time gained 2.2 dementia-free years, and 2.7 years of life when compared with those who remained unfit at both assessments.