Associations of a Vitamin D Behavior Index with Health and Functional Characteristics in Older Women

Objectives This study examined associations between a vitamin D (VD) behavior index (awareness, intake, and sun exposure) and body composition, senior fitness, physical activity, and health behaviors, and identified key correlates of the VD behavior index in older women. Methods A cross-sectional study was conducted with 300 community-dwelling women aged 65–80 years in G Province, Korea. Participants completed structured questionnaires assessing the VD behavior index, physical activity (K-GPAQ), and health behaviors (smoking and alcohol use), and underwent standardized assessments of body composition (InBody 720) and senior fitness (National Fitness 100 [Senior]). Pearson correlation and regression analyses were performed. Results In the body-composition model, muscle mass was the only significant positive correlate of the VD behavior index (β = 0.613, adj. R² = 0.394). In the senior-fitness model, lower-limb function showed the strongest association (β = 0.318), and upper-limb function (β = 0.261), balance (β = 0.214), and cardiorespiratory endurance (β = 0.185) were also positively associated (adj. R² = 0.263). Physical activity was positively associated with the VD behavior index (β = 0.371, adj. R² = 0.134). Health behaviors were statistically significant but explained little variance (β = 0.125, adj. R² = 0.012). Conclusions Higher VD-related behaviors were associated with greater muscle mass and better functional capacities—particularly lower-limb function, balance, and endurance—in older women. Given the cross-sectional design, causal inference is not warranted; however, these findings highlight potential targets for future intervention studies integrating resistance-based training, outdoor physical activity, and VD education (safe sun exposure, diet, and supplementation guidance).