 His work was on fluorine and the prevention of tooth decay, vitamins D and E, and the effect of a slew of trace minerals in nutrition, including aluminum, calcium, cobalt, phosphorus, potassium, manganese, sodium, strontium, and zinc.McCollum worked with Herbert Hoover's U.S. Food Administration to help those who were starving in Europe following World War I. Hoover sent him on a lecture tour of all the major cities in the western U.S., where McCollum explained that the American diet was of poor quality, and that it would be better to eat organ meats (rather than muscle meats), fewer potatoes, and less sugar.In conversation with John Howland, a Johns Hopkins pediatrician, and later with Howland's staff doctors Edwards A.