Physical fitness and incident mild cognitive impairment: a systematic review

Background
Higher physical fitness is associated with various health outcomes, including decreased dementia risk. Little is known as to whether physical fitness is also associated with new onset of mild cognitive impairment (MCI). Our aim was to provide an overview of longitudinal research on the associations between physical fitness and the risk of incident MCI.

Methods
We conducted a systematic literature review that examined associations between different components of physical fitness such as strength or endurance with incident MCI in older adults. We searched PubMed, Scopus, and Web of Science databases for longitudinal and/ or prospective cohort studies published in English or German. Screening was performed independently by two authors, and quality of included studies was assessed using the Newcastle Ottawa Scale.

Results
The search yielded 12,298 studies, of which 19 were included in the review, with follow-up times ranging from 2 to 26 years, and sample sizes ranging from 87 to 995,243 persons. Thirteen studies that examined associations between strength, variables related to muscle quality and function with incident MCI revealed inconsistent findings, e.g., six studies showed that lower handgrip strength was associated with higher MCI risk or that higher handgrip strength was associated with decreased MCI risk, respectively; while five studies reported no associations between handgrip strength and MCI risk or only for females. ... mehrOne study reported associations between lower cardiovascular fitness and increased risk of MCI. Twelve studies examined associations between balance, mobility and gait-related variables, mainly focusing on gait speed, but results were inconsistent, e.g., while some reported associations between slower gait speed and increased MCI risk, others did not or only in subgroups. Five studies reported associations between higher global/ composite fitness scores and decreased risk of incident MCI. Quality of included studies was rated as good.

Conclusion
Higher cardiovascular and overall physical fitness is associated with a decreased risk of incident MCI. There are inconsistent associations between strength, balance- or gait-related variables and MCI risk. These findings indicate the importance of overall and cardiovascular physical fitness to potentially delay new onset of MCI. More research is needed to confirm these observations, and to untangle mechanisms underlying the associations between physical fitness components and MCI risk.