Resting metabolic rate in relation to incident disability and mobility decline among older adults: the modifying role of frailty

Background: Alterations in resting metabolic rate (RMR), the largest component of daily total energy expenditure, with aging have been shown in various studies. However, little is known about the associations between RMR and health outcomes in later life. Aims: To analyze whether RMR is associated with incident disability and mobility decline in a 10-year longitudinal study, as well as the moderating role of frailty in these associations. Methods: Data from 298 older adults aged 70 and over from the Frailty and Dependence in Albacete (FRADEA) study in Spain were used, including a baseline measurement in 2007–2009 and a follow-up measurement 10 years later. RMR was measured by indirect calorimetry. Outcomes were incident disability in basic activities of daily living (BADL, Barthel Index), incident disability in instrumental ADL (IADL, Lawton index), and mobility decline (Functional Ambulation Categories scores). Fried’s frailty phenotype was used as an indicator of frailty. Logistic regression analyses were conducted. Results: Fully adjusted and stratified analyses revealed that only in the pre-frail/frail group, a higher RMR was associated with a lower risk of incident BADL disability (OR = 0.47, 95% CI = 0.23–0.96, p = 0.037), incident IADL disability (OR = 0.39, 95% CI = 0.18–0.84, p = 0.017), and mobility decline (OR = 0.30, 95% CI = 0.14–0.64, p = 0.002). Conclusions: To our knowledge, this is the first study looking at the associations between RMR and functional health using a longitudinal research design. The results suggest that RMR could be used as an early identifier of a specific resilient group within the pre-frail and frail older population, with a lower risk of further health decline.