The risks of one-at-a-time biomarker epidemiology: Associations of circulating calcium levels with age, mortality, and frailty vary substantially across populations

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Publication date
2017Author(s)
Cohen, Alan; Legault, Véronique; Fuellen, Georg; Fülöp, Tamàs; Fried, Linda P.; Ferrucci, Luigi
Editor(s)
Université de Sherbrooke. Groupe de recherche PRIMUS
Rostock University Medical Center. Institute for Biostatistics and Informatics in Medicine and Ageing Research, IBIMA
Université de Sherbrooke. Centre de recherche sur le vieillissement
Columbia University. Mailman School of Public Health
MedStar Harbor Hospital. Translational Gerontology Branch, Longitudinal Studies Section, National Institute on Aging, National Institutes of Health
Subject
Aging biomarkersAbstract
Abstract: Recent studies have shown contradictory associations between calcium levels and health outcomes. We suspected these conflicting results were the consequence of more general
issues with how biomarkers are analyzed in epidemiological studies, particularly in the context of aging. To demonstrate the risks of typical analyses, we used three longitudinal
aging cohort studies and their demographic subsets to analyze how calcium levels change with age and predict risk of mortality and frailty. We show that calcium levels either increase or decrease with age depending on the population, and positively or negatively predict frailty depending on the population; both age and frailty results showed substantial heterogeneity. Mortality analyses revealed few significant associations but were likely
underpowered. Variation in population composition (demographics, diseases, diet, etc.) leads to contradictory findings in the literature for calcium and likely for other biomarkers. Epidemiological studies of biomarkers are particularly sensitive to population composition both because biomarkers generally have non-linear and often non-monotonic relationships with other key variables, notably age and health outcomes, and because there is strong interdependence among biomarkers, which are integrated into complex regulatory networks. Consequently, most biomarkers have multiple physiological roles and are implicated in multiple pathologies. We argue that epidemiological studies of aging using biomarkers must account for these factors, and suggest methods to do this.
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