This week, Collected Wisdom grabs its white trench coat, dons a fedora and heads out onto the dark, rainy streets to solve the Case of the Missing Vitamins.
Why are there vitamins A through E, and then nothing until vitamin K? What happened to vitamins F through J? And why are there many different vitamin Bs? Catharine Bird of Toronto wants to know.
First, it might be helpful to define what a vitamin is. According to Stedman's Medical Dictionary, it is one of a group of organic substances, present in minute amounts in natural foodstuffs, that are essential to normal metabolism.
And now, to answer the question, here's Robin Marles, a director of Health Canada's Natural Health Products Directorate in Ottawa. "In the early part of the 20th century," he writes, "animal-nutrition researchers discovered an essential nutrient in butterfat that they called vitamin A (retinol) and a water-soluble essential nutrient from milk that they called vitamin B."
When vitamin B was found to include many biological and chemical functions, he says, the collective term "vitamin B complex" was adopted. These different functions are due to separate water-soluble substances, named B1 (thiamine), B2 (riboflavin), B3 (niacin, niacinamide), B5 (pantothenic acid), B6 (pyridoxine, pyridoxal, pyridoxamine), B7 (biotin), B9 (folic acid) and B12 (cyanocobalamin). "The substance originally identified as B4 has now been identified as adenine, and is not considered a vitamin because our body can synthesize it," he writes. "B8 was later identified as adenylic acid. Similarly, other substances originally categorized as B vitamins were found to not meet the definition of a vitamin."
The substance found in fresh fruit and vegetables that can be used to treat or prevent scurvy, a disease known in people lacking access to fresh food, was finally identified in the 1930s as ascorbic acid, known as vitamin C, Dr. Marles says.
"As more vitamins were discovered, they were at first given further letters of the alphabet, e.g. vitamin D (D2 is ergocalciferol, D3 is cholecalciferol), vitamin E (alpha-tocopherol), and vitamin K (K1 is phylloquinone, K2 is menaquinone)."
The substances originally identified as vitamin F, he says, were subsequently shown to be the essential unsaturated fatty acids, which are needed in substantial rather than trace amounts, not fitting the definition of a vitamin.
"Vitamin G is an obsolete name for riboflavin (now B2). H was the original name for biotin (now B7). There is no record of a historical vitamin I. Vitamin J has been associated with either riboflavin or the non-essential substance catechol, and M is an obsolete name for folic acid (B9). Substances formerly referred to as vitamins L (anthranilic acid), N (thioctic or alpha-lipoic acid), O (carnitine), and P (flavonoids) are other examples of nutrients that do not meet the modern definition of a vitamin."
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- Why are some sports arenas called “gardens” (as in Madison Square Garden or Maple Leaf Gardens)? Mary Lehane of Toronto wants to know.
If you have the answer to one of these questions (or want to pose a question) send an e-mail to email@example.com. Please include your name, location and a daytime phone number.