Amount of population in the world who suffer iodine deficiency is:

The World Health Organization (WHO) estimates that about 2 billion people are iodine-deficient, based on urinary excretion data. Iodine deficiency is prevalent in many mountainous regions and in central Africa, central South America, and nohern Asia. In areas of relative iodine deficiency, there is an increased prevalence of goiter and, when deficiency is severe, hypothyroidism and cretinism. Ref: Weetman A.P., Jameson J.L. (2012). Chapter 341. Disorders of the Thyroid Gland. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.