Change in vitamin D concentration in obese individuals after a six-month weight loss intervention of high- versus low-carbohydrate diets

Vitamin D deficiency is common among individuals with overweight and obesity, yet the impact of weight loss on vitamin D status remains unclear. This randomized controlled trial examined changes in serum 25‑hydroxyvitamin D [25(OH)D] concentrations following a six‑month high‑ or low‑carbohydrate weight‑loss intervention. Among 119 participants, 92% were vitamin D insufficient and 40% were deficient at baseline, with little improvement after weight loss despite significant reductions in weight and fat mass. Changes in 25(OH)D were not associated with diet type or weight loss. These findings suggest that weight loss alone does not improve vitamin D status, highlighting the need for supplementation among individuals with overweight or obesity, particularly in regions with limited sun exposure.