"Long COVID was frequently observed in children with vitamin D deficiency/insufficiency (p = 0.0331). The odds of developing long COVID were 2.2 times higher (p = 0.0346) in children with vitamin D deficiency/insufficiency compared to those with optimal levels."
https://www.frontiersin.org/journals/pediatrics/articles/10.3389/fped.2025.1507169/full