Effect of Excess Weight on 25-Hydroxyvitamin D Levels

Children with excess weight frequently exhibit lower serum 25-hydroxyvitamin D (25(OH)D) concentrations than their normal weight peers, yet it remains uncertain whether vitamin D-related biochemical profiles differ across weight categories. This study evaluated serum 25(OH)D, parathyroid hormone (PTH), alkaline phosphatase (ALP), albumin, calcium, phosphorus, and magnesium in relation to weight status.

This retrospective cross-sectional analysis included 544 children and adolescents aged 1-18 years with 25(OH)D ≤20 ng/mL who presented to a pediatric endocrinology clinic between April 2023 and March 2025. Of these, 304 had excess weight. Vitamin D deficiency (<12 ng/mL) was identified in 224 participants (138 with excess weight), and insufficiency (12-20 ng/mL) in 320 (166 with excess weight). Weight status was classified according to body mass index percentiles.

Overall, 55.9% of participants were overweight/obese. Vitamin D deficiency was more prevalent in this group (P = .024). However, mean concentrations of 25(OH)D, PTH, ALP, albumin, calcium, phosphorus, and magnesium were comparable between weight groups. Independent of weight status, vitamin D deficiency was associated with higher PTH and lower calcium compared with insufficiency. Within the insufficiency subgroup, children with excess weight demonstrated higher PTH levels. Correlation patterns were consistent across weight categories: 25(OH)D correlated positively with calcium and inversely with PTH; ALP correlated positively with phosphorus; and PTH correlated inversely with calcium.

Among children with vitamin D deficiency or insufficiency, biochemical markers were broadly similar regardless of weight status. These findings reinforce current recommendations for vitamin D and calcium intake for all pediatric populations, independent of body weight.