VDR and obesity due to melanocortin 4 receptor deficiency: First, detailed information about confounding factors such as ethnicity, physical activity, baseline HbA1c, body mass index, obesity, sun exposure, seasonal changes in vitamin D, dietary vitamin D intake, calcium intake, vitamin D receptor polymorphisms, baseline vitamin D status, and compliance with vitamin D supplements that could influence the response of vitamin D was not available in all of the included studies [49].