Lippi, Giuseppe, et al. “The Burden of Vitamin D Deficiency in a Mediterranean Country Without a Policy of Food Fortification”. Acta Biomedica Atenei Parmensis, vol. 86, no. 1, Apr. 2015, pp. 59-62, https://mattioli1885journals.com/index.php/actabiomedica/article/view/4243.