I was struck by a television commercial for Nature Made vitamins that referred to letter vitamins. As opposed to what?, I wondered.
Here it is on the company’s on-line site:
How do you choose a vitamin brand?
There are lots of vitamin brands out there. For 40 years, Nature Made has been a vitamin and supplement company dedicated to quality. That’s one of the reasons Nature Made was chosen as the #1 Pharmacist Recommended Letter Vitamin and Fish Oil brand in the 2011 Pharmacy Times survey.
From this text, it’s clear that fish oil doesn’t count as a letter vitamin. Well, fish oil doesn’t supply vitamins; it supplies omega-3 fatty acids, and fatty acids are a class of nutrients distinct from vitamins (minerals and amino acids are two other classes). But you can see some piece of a categorization of dietary supplements in the pharmacists’ world. More of this categorization appears in the full list of categories in which Nature Made was ranked #1 in the Pharmacy Times survey (reported on here):
Letter Vitamins (A, B, C, D, and E), CoQ10, Omega-3/Fish Oil, Flax Seed Oil, Herbal Supplements, Diabetic Multivitamin, Garlic Supplement
Most of the things that follow letter vitamins on this list are not vitamins: flax seed oil is a source of another type of omega-3 fatty acid; herbal supplements and garlic supplements are taken for their (putative) medicinal values and are not nutrients; and Coenzyme Q10, or CoQ10, is another supplement used for its medicinal value. That leaves us with diabetic multivitamins, and that’s the clue: letter vitamins are tablets that supply a single specific vitamin (identified by letter), in contrast to multivitamin tablets or multivitamin/multimineral tablets.
So letter vitamin is a technical term in the pharmacist world. The Nature Made commercial quoted the term from the Pharmacy Times ratings; a reader of Pharmacy Times and similar sources would be familiar with the term, but ordinary television viewers probably would not be. I imagine that most people, hearing the commercial, just treat letter vitamins as a fancy way of saying vitamins.