Associations between physical frailty, physical activity and dementia incidence
Authors: Martin Kopp, Martin Burtscher
Journal: The Lancet Healthy Longevity (2021)

We read with great interest the excellent study on the association between physical frailty and dementia that was recently published in The Lancet Healthy Longevity.1Petermann-Rocha F Lyall D Gray S et al.Associations between physical frailty and dementia incidence: a prospective study from UK Biobank.Lancet Healthy Longev. 2020; 1: e58-e68Summary Full Text Full Text PDF Scopus (16) Google Scholar Based on a large cohort, the authors showed that four of five components defining frailty—ie, weight loss, tiredness, low grip strength, and slow gait speed—were independently associated with a higher risk of dementia incidence. Although grip strength and gait speed had the largest contributions, no association was shown between physical activity (PA) and the risk of dementia incidence.1Petermann-Rocha F Lyall D Gray S et al.Associations between physical frailty and dementia incidence: a prospective study from UK Biobank.Lancet Healthy Longev. 2020; 1: e58-e68Summary Full Text Full Text PDF Scopus (16) Google Scholar This finding is a bit surprising, and the reader could gain the impression that PA does not have an important role in the development of dementia, which might be discouraging and could negatively affect adherence to regular PA and, therefore, healthy aging and longevity.2Burtscher J Burtscher M Run for your life: tweaking the weekly physical activity volume for longevity.Br J Sports Med. 2019; 54: 759-760Crossref PubMed Scopus (10) Google Scholar It seems logical that low grip strength and slow gait speed are correlated with the level of PA. Although the authors applied sophisticated statistical methods, it is unclear whether multicollinearity has been appropriately considered in the Cox proportional hazard models. Moreover, the numbers for the PA levels provided in metabolic equivalents (MET-h) per week are difficult to understand. Although only baseline characteristics were shown, the large difference between non-frail versus frail (2493 MET-h [IQR 1422·0–4506·0] vs 540 MET-h [346·5–990·0]) is obvious, strongly suggesting a close association between PA and frailty and, thus, also between frailty and the incidence of dementia. A dose–response association between PA and several physical performance measures, including grip strength and gait speed, has been convincingly shown for both sexes.3Laddu D Parimi N Cauley JA et al.The association between trajectories of physical activity and all-cause and cause-specific mortality.J Gerontol A Biol Sci Med Sci. 2018; 73: 1708-1713Crossref PubMed Scopus (10) Google Scholar, 4Laddu DR Parimi N Stone KL et al.Physical activity trajectories and associated changes in physical performance in older men: the MrOS study.J Gerontol A Biol Sci Med Sci. 2020; 75: 1967-1973Crossref PubMed Scopus (6) Google Scholar Moreover, a meta-analysis of prospective studies showed a dose–response trend for all-cause dementia and Alzheimer's disease (ie, an average decrease of 10% and 13% in the risk of all-cause dementia and Alzheimer's disease for every 10 MET-h increase per week).5Xu W Wang HF Wan Y Tan CC Yu JT Tan L Leisure time physical activity and dementia risk: a dose-response meta-analysis of prospective studies.BMJ Open. 2017; 7e014706Crossref PubMed Scopus (65) Google Scholar Because an associated decrease in risk of dementia with regard to the level of PA might also apply to the study by Petermann-Rocha and colleagues, the health benefits of PA should be more explicitly shown. We declare no competing interests. Associations between physical frailty and dementia incidence: a prospective study from UK Biobank – Authors' replyWe thank Martin Kopp and Martin Burtscher and Alberto Sardella and colleagues for their interest in our work.1 Kopp and Burtscher raised the issue that the finding of no association between low levels of physical activity (PA) and dementia risk reported in our study could send the wrong message to the public, by discoursing and negatively affecting adherence to regular PA. Despite reporting no association between the level of PA and dementia risk in our study, we cannot deny the health benefits of being physically active. Full-Text PDF Open AccessAssociations between physical frailty and dementia incidence: a prospective study from UK BiobankIndividuals with pre-frailty and frailty were at a higher risk of dementia incidence even after adjusting for a wide range of confounding factors. Early detection and interventions for frailty could translate into prevention or delayed onset of dementia. Full-Text PDF Open Access