T, V, W, X, Y or Z, nor are there substances officially designated as vitamins N or I, although the latter may have been another form of one of the other vitamins or a known and named nutrient of another type. See also Vitamin deficiency Hypervitaminosis Human nutrition References External links USDA RDA chart in PDF format Health Canada Dietary Reference Intakes Reference Chart for Vitamins NIH Office of Dietary Supplements: Fact Sheets Essential nutrients Nutrition