Dramatic Deterioration of Subclinical Hyperparathyroidism in Children and Adolescents During the Post-COVID-19 Period

<b>Background:</b> Vitamin D is a steroid hormone, essential for the immune system and bone health. Since the sun is meant to provide at least 80% of daily vitamin D requirements, the COVID-19 pandemic is likely to have induced a considerable influence on calcium metabolism. <b>Methods:</b> We analyzed data from 1138 children, seen in an outpatient pediatric endocrinology clinic from 2022-2023. Vitamin D status was classified as deficiency if 25(OH)D ≤ 20 ng/mL, insufficiency < 30 ng/mL, and sufficiency ≥ 30 ng/mL. <b>Results:</b> Overall, 60.8% of children had vitamin D deficiency or insufficiency worsened with age (<i>p</i> < 0.005), and with adolescent males having higher 25(OH)D concentrations than females (<i>p</i> < 0.05). A negative correlation was found between 25(OH)D and BMI SDS (<i>R</i>² = 0.02, <i>p</i> < 0.001), and 25(OH)D concentrations varied seasonally, decreasing in winter. Subclinical hyperparathyroidism [parathyroid hormone (PTH) > 45 pg/mL) and normal calcium] was found in 21.5% of children, with 73.5% of them being vitamin D deficient or insufficient. A negative correlation between PTH and 25(OH)D was observed, with PTH plateauing at 25(OH)D above 40 ng/mL (<i>p</i> < 0.001). <b>Conclusions:</b> Compared to the pre-pandemic data (2016-2018), with only 5.1% of children having subclinical hyperparathyroidism (<i>p</i> < 0.001), these findings suggest a marked deterioration in vitamin D status and calcium metabolism in children, with possible unforeseen consequences for bone, immune, and general health.