PTH and Insulin resistance: Aypak et al. (2013) showed nearly universal deficiency in Turkish children, with stronger associations in females and pubertal adolescents, and identified potential links to insulin resistance. Ethnic disparities have also been reported: Ford et al. (2006) highlighted higher deficiency rates among Asian and Black Afro-Caribbean groups in the UK, especially among women. Sahota et al. (2004) showed moderate seasonal variation and a clear inverse correlation between 25(OH)D and PTH levels, underlining potential effects on calcium homeostasis.