It’s also not entirely clear how many people have anosmia. In 2012, research analyzing the U.S. National Health and Nutrition Examination Survey estimated that 23 percent of Americans over the age of 40 report some alteration to their sense of smell. A 2016 paper that examined results from a later version of same survey estimated that more than 12 percent of American adults had some sort of olfactory dysfunction. And Fifth Sense, a charity for smell and taste disorders, estimates that 1 in 10,000 people have congenital anosmia.
— Read more in The Study of Smell Loss Still Struggles for Support at Undark.