Factors influencing serum 25-hydroxivitamin D levels and other bone metabolism parameters in healthy older women

Objective: Older women have frequently low serum 25-hydroxivitamin D (25[OH]D) concentrations, high parathormone (PTH) levels and low bone mineral density (BMD) values. Endogenous synthesis, dietary habits, sunlight exposure and fat-mass-mediated storage may influence 25(OH)D levels and bone metabolism, but the relevance of these factors in the elderly has yet to be fully elucidated. We aimed to investigate the influence of dietary vitamin D intake and fat mass on serum 25(OH)D levels and bone metabolism in older women. Design: Cross-sectional. Setting: Community. Participants: 218 fit older women attending a biweekly mild fitness program. Measurements: Dietary habits was investigated through a 3-day record questionnaire. Serum 25(OH)D and intact parathormone (PTH) concentrations were measured by radioimmunoassay and by a 2-step immunoradiometric assay, respectively. BMD and body composition were estimated using dualenergy X-ray absorptiometry with fan-beam technology. Results: Only fat mass showed a significant negative association with 25(OH)D (β=-3.76, p