Wednesday, March 31, 2021

Biotin - a Not-Exciting B Vitamin

Biotin – one of the thirteen vitamins needed for humans to be heathy – gets no respect. No one won a Nobel Prize for elucidating the mysteries of biotin. Perhaps that is because it is near-impossible to be deficient for this vitamin, plus evidence is weak for any confirmed benefit when used as dietary supplement.

Per Wikipedia article “Vitamin,” the golden age of vitamin discovery was 1910 to 1940, with vitamin B12 as an outlier, in 1948. Early on, discoveries were back and forth between fat soluble vitamins A, D, E and K, and water-soluble, named as B and C. “Vitamin B” actually turned out to be a whole bunch of vitamins. The discovery timeline finished with B5 (pantothenic acid), B6, B7 (biotin), B9 (folate) and B12.

The present-day “B” numeration for vitamins is missing numbers. B4 and B8 turned out to be compounds that are not essential, as they are synthesized in the body. B10 (also called “Bx”) was assigned to para-aminobenzoic acid, a substance found in some foods, and convertible to folate by plants and bacteria. It turned out to not be essential for animals. Known also by its acronym “PABA,” this compound was commonly used as a sunscreen chemical stating in the 1970s, because it absorbs ultraviolet light. However, in 2019, the U.S. Food and Drug Administration designated PABA as NOT Generally Recognized as Safe and Effective, because it can trigger allergic reactions, and is suspected of being promoter of skin cancer.

B11, another discarded number, was initially applied to a compound that turned out to be a derivative of folate, hence not a vitamin in its own right. In fact, many vitamins are actually a family of chemically related and sometimes metabolically convertible compounds, referred to as “vitamers.” For example, food-derived folates can be chemically different from each other, and from folic acid, the form used in dietary supplements, but all can be converted to the biologically active tetrahydrofolic acid. “Vitamin E” consists of eight vitamers, of varying levels of potency.

Biotin was “discovered,” meaning identified as a food-sourced compound essential in the diet, in a round-about way. In 1916, a diet high in raw egg whites was proven to cause toxic symptoms in humans and test animals. This included hair loss, skin problems and neurological dysfunction – all reversed when the diet was changed. Was this a toxin that could be inactivated by heat? Research groups working independently in several countries isolated the egg factor in the 1930s. As it turns out, raw and partially cooked egg white did not contain a toxin, but rather contained a heat-inactivated protein, avidin, that irreversibly bound itself to a compound given the names “biotin, vitamin H” and “cofactor-R.” Biotin became the agreed upon name in 1940.    

Chemical structure of biotin
Biotin’s main function is as a cofactor to several carboxylase enzymes involved in the synthesis of fatty acids and glucose. Deficiency is rare for two reasons: biotin is contained in a wide range of foods, and because biocytin, the major metabolic breakdown product, is recycled into biotin rather than being excreted in urine. For humans, 30 micrograms a day appears to be a safely sufficient amount. According to the Global Fortification Data Exchange, biotin deficiency is so rare that no countries require that foods be fortified.

Biotin is sold in the United States as a dietary supplement, with vaguely worded claims that it will improve hair, fingernail and skin health. The rationale behind this is that deficiency symptoms include brittle and thin fingernails, hair loss and skin rash. While biotin has been proven to improve hoof health in horses and cattle, the evidence that it can have any effects in humans who are not biotin deficient is weak. For fingernails, there were a few clinical trials conducted without placebo controls, published more than 30 years ago. For hair, not even that much in the way of scientific evidence. And yet, it is sold in amounts more than 100 times the requirement.

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