Temporal Changes in Cardiorespiratory Fitness and Risk of Dementia Incidence and Mortality - Results from the HUNT Study

Background: Cardiorespiratory fitness (CRF) is associated with risk of dementia, but it is not known whether temporal changes in CRF influence the risk of dementia incidence- and mortality. Methods: Data from the prospective Nord-TrA¸ndelag Health Study (HUNT, n=30,695) was linked to dementia incidence and cause of death registries. CRF was assessed on two occasions 10 years apart, and the second assessment was used as baseline for follow-up. Using Cox proportional hazard analyses, adjusted hazard ratios (AHR) were estimated for dementia incidence- and mortality related to temporal changes in CRF. Findings: 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 unfit participants at both assessments, participants who sustained high CRF had 40% reduced risk of incident dementia (AHR: 0.60; 95% CI: 0.36-0.99), and 44% reduced risk of dementia mortality (AHR: 0.56; 95% CI: 0.43-0.75). Participants who increased their CRF over time, reduced the risk of incident dementia and dementia mortality with 48% (AHR: 0.52; 95% CI: 0.30-0.90), and 28% (AHR: 0.72; 95% CI: 0.52-0.99), respectively. Each MET increase in CRF was associated with 16% and 10% relative risk reduction of incident dementia and dementia mortality, respectively. Participants who increased their CRF over time gained 2.2 (95% CI: 1.0-3.5) dementia free years, and 2.7 (95% CI: 0.4-5.8) years of life. Interpretation: Maintaining or improving CRF over time may be a target to reduce risk of dementia- incidence and mortality, delay onset and increase longevity after diagnosis. Our data highlight the importance of assessing CRF in health risk assessment for people at risk of dementia. Funding Statement: The K.G. Jebsen Foundation, the Norwegian Research Council, the Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology. Declaration of Interests: All authors declare no competing interests. Ethics Approval Statement: The study was approved by the Data Inspectorate and the Regional Committee on Medical and Health Research Ethics of Norway (2015/2015/REK midt).