The interplay between childhood obesity and vitamin D deficiency: mechanisms and implications

Childhood obesity and vitamin D deficiency (VDD) are intertwined global health threats that amplify each other beyond their individual skeletal or metabolic consequences. This review synthesises a decade of clinical, translational and Mendelian-randomisation evidence to show that obesity drives VDD through volume dilution, adipose-tissue sequestration and metabolic associated steatotic liver disease (MASLD)-related hydroxylase dysfunction, while VDD in turn aggravates adipogenesis, leptin resistance and chronic low-grade inflammation, locking children into a self-perpetuating cycle. Meta-analysis of 12 randomised trials ( n = 1,538) revealed that vitamin D supplementation improves insulin sensitivity and lowers systolic blood pressure only when baseline 25-hydroxyvitamin D (25(OH)D) is