Obesity may extend the time required to reach a steady-state 25-hydroxyvitamin D level after initiating vitamin D supplementation

Authors: DAWSON-HUGHES, BESS - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; KONIECZYNSKI, ELSA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; CEGLIA, LISA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Journal of Bone and Mineral Research Plus
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2025
Publication Date: 4/15/2025
Citation: Dawson-Hughes, B., Konieczynski, E.M., Ceglia, L. 2025. Obesity may extend the time required to reach a steady-state 25-hydroxyvitamin D level after initiating vitamin D supplementation. Journal of Bone and Mineral Research Plus. 9(4). Article ziaf030. https://doi.org/10.1093/jbmrpl/ziaf030.
DOI: https://doi.org/10.1093/jbmrpl/ziaf030

Interpretive Summary: Obesity is associated with lower vitamin D status, but whether obesity influences the time required to reach a stable circulating 25-hydroxyvitamin D [25(OH)D] level after starting vitamin D supplementation is unknown. We examined the timing of change in 25(OH)D levels in normal weight and over-weight and obese adults who participated in the STOP IT clinical trial. In 167 adults who were treated with 700 IU of vitamin D daily, those of normal weight had reached stable 25(OH)D level by 6 months whereas in the over-weight and obese adults, 25(OH)D levels continued to rise between 6 and 12 months. This analysis suggests that the time required to reach a steady-state 25(OH)D level after initiating vitamin D supplementation in overweight and obese adults is greater than the usual 3-month time point commonly used in clinical practice. A more refined definition of the time course of circulating 25(OH)D response to supplementation is needed in overweight and obese individuals in order to optimize monitoring of their vitamin D status.

Technical Abstract: Obesity is known to influence the circulating 25-hydroxyvitamin D [25(OH)D] level but less is known about whether it influences the time required to reach a stable 25(OH)D level after initiating vitamin D supplementation. This observational study was done to investigate whether body mass index (BMI) modified the time required to reach a steady-state 25(OH)D level in response to vitamin D supplementation. Participants in the Boston STOP IT study who were treated for 12 months with 700 IU of vitamin D3 and 500 mg of calcium daily and had 25(OH)D measures at 0, 6, and 12 months, were included. We assessed the trajectory of 25(OH)D levels by baseline BMI category (normal weight, BMI 18.5-24.9 kg/m2, N = 62; overweight and obese, BMI = 25 kg/m2, N = 105). Baseline 25(OH)D levels were 78 + or -31.3 nmol/L (normal weight) and 74.7 + or - 36.5 nmol/L (overweight and obese). In a linear mixed model examining the influence of time and baseline BMI category on change in the mean 25(OH)D level, there was a significant time x BMI group interaction (P = 0.024. The normal weight participants had reached steady-state 25(OH)D levels by 6 months whereas 25(OH)D levels continued to rise between 6 and 12 months in the overweight and obese participants. This analysis suggests that the time required to reach a steady-state 25(OH)D level after initiating vitamin D supplementation in overweight and obese adults is greater than the usual 3-month time point commonly used in clinical practice. A more refined definition of the time course of circulating 25(OH)D response to supplementation is needed in overweight and obese individuals in order to optimize clinical monitoring of vitamin D status.