GÜMÜRDÜLÜ, Yüksel, et al. “Predictors of Vitamin B-12 Deficiency: Age and Helicobacter Pylori Load of Antral Mucosa”. Turkish Journal of Gastroenterology, vol. 14, no. 1, Jan. 2003, pp. 44-49, https://www.turkjgastroenterol.org/index.php/tjg/article/view/1235.