Combined Effect of Dynapenia (Muscle Weakness) and Low Vitamin D Status on Incident Disability

Abstract

Background and objectiveThere is little epidemiologic evidence considering the combined effect of dynapenia and low 25-hydroxyvitamin D [25 (OH) D] on incident disability. Our aim was to investigate whether the combination of dynapenia and low 25 (OH) D serum levels increases the risk of activities of daily living (ADL) incident disability. DesignProspective cohort study. SettingsEnglish Longitudinal Study of Aging. ParticipantsA total of 4630 community-dwelling adults aged 50 years and older without ADL disability at baseline. MeasurementsThe baseline sample was categorized into 4 groups (ie, nondynapenic/normal 25 (OH) D, low 25 (OH) D only, dynapenic only, and dynapenic/low 25 (OH) D according to their handgrip strength (<26 kg for men and <16 kg for women) and 25 (OH) D (≤50 nmol/L). The outcome was the presence of any ADL disability 2 years after baseline according to the modified Katz Index. Incidence rate ratios (IRRs) adjusted by sociodemographic, behavioral, and clinical characteristics were estimated using Poisson regression. ResultsThe fully adjusted model showed that older adults with dynapenia only and those with lower serum levels of 25 (OH) D combined with dynapenia had higher incident ADL disability risk compared with nondynapenic and those with normal serum levels of 25 (OH) D. The IRRs for lower 25 (OH) D serum levels combined with dynapenia were higher than for dynapenia only, however, the confidence intervals (CIs) showed similar effect for these 2 groups. The IRRs were 1.31 for low 25(OH) D only (95% CI 0.99–1.74), 1.77 for dynapenia only (95% CI 1.08–2.88), and 1.94 for combined dynapenia and low 25(OH)D (95% CI 1.28–2.94). ConclusionsDynapenia only and dynapenia combined with low 25 (OH) D serum levels were important risk factors for ADL disability in middle-aged individuals and older adults in 2 years of follow-up.