4.4: Vitamins

The other essential molecules needed in our diet are called vitamins. There are 13 vitamins, grouped by whether they dissolve in fat or water. Vitamins A, D, E, and K are fat-soluble. Vitamin C and the eight B-vitamins (biotin, folate, niacin, pantothenic acid, riboflavin, thiamin, B₆, and B₁₂) are water-soluble.

Knowing whether they dissolve in fat or water has practical value. If you boil vegetables in water and discard the water, you lose some of the vegetable’s water-soluble vitamins. Also, the body can rid itself of excess water-soluble vitamins in the urine. Excess fat-soluble vitamins can’t be excreted this way and are thus more likely to be toxic in big doses. (As with the disease PKU, discussed in the previous chapter, a familiar theme is that accumulating large amounts of even an essential substance can be harmful.)

The vitamins are listed in Appendix A-5 along with some of their functions, food sources, and symptoms of deficiency and toxicity.

The hodgepodge of names given to vitamins is confusing. It began logically. In 1920, scientists thought there were three vitamins—A, B, and C. But vitamin B turned out to be eight vitamins, and some that were thought to be vitamins (e.g., B₁₁) didn’t turn out to be. The naming was then in confusion, and vitamins were given alternate names, e.g., B₁₂ contains cobalt and is also called cobalamin. It also was found that vitamins can occur in several forms. Adding to the confusion, some substances can be converted to vitamins in the body, e.g., the amino acid tryptophan can be converted into the B-vitamin niacin.

Sometimes substances are promoted as vitamins when they really aren’t. Pangamic acid has been called vitamin B₁₅ and promoted for treating various ills. Laetrile has been called vitamin B₁₇ and promoted for treating cancer. Neither are vitamins and have no known value in treating illness or maintaining health. But there’s monetary value in naming substances vitamins—it helps make millions of dollars for their promoters.