25-Hydroxyvitamin D, Insulin-Like Growth Factor-I, and Bone Mineral Accrual during Growth

Context: The extent to which 25-hydroxyvitamin D [25(OH)D] and IGF-I influence bone mineral content (BMC) accrual from early to mid-puberty is unclear. Objective, Setting, and Participants: This study sought to determine relationships among 25(OH)D, IGF-I, and BMC in community-dwelling prepubertal females (n = 76; aged 4–8 yr at baseline) over a period of up to 9 yr. Design: The hypothesis that changes in IGF-I vs. 25(OH)D are more strongly associated with BMC accrual was formulated after data collection. 25(OH)D and IGF-I were log-transformed and further adjusted using two-way ANOVA for differences in season and race. Linear mixed modeling (including a random subject-specific intercept and a random subject-specific slope on age) was employed to analyze the proportion of variance the transformed 25(OH)D and IGF-I variables explained for the bone outcomes. Results: IGF-I was more strongly associated with BMC accrual than 25(OH)D at the total body (R2 = 0.874 vs. 0.809), proximal femur (R2 = 0.847 vs. 0.771), radius (R2 = 0.812 vs. 0.759), and lumbar spine (R2 = 0.759 vs. 0.698). The rate of BMC accrual was positively associated with changes in IGF-I but negatively associated with 25(OH)D. When IGF-I and 25(OH)D were included in the same regression equation, 25(OH)D did not have a significant predictive effect on BMC accrual above and beyond that of IGF-I. Conclusions: These prospective data in early adolescent females indicate that both 25(OH)D and IGF-I have a significant impact on bone mineral accrual; however, the positive association of IGF-I and BMC accrual is greater than the negative association of 25(OH)D and BMC accrual. Both 25(OH)D and IGF-I impact bone mineral accrual; however, the positive association of IGF-I is greater than the negative association of 25(OH)D on BMC accrual.