10.8 Biotin (Vitamin B7)

Biotin (Vitamin B7)

Biotin is a water-soluble B vitamin that is primarily found in 2 dietary forms; free biotin and

biocytin (a.k.a. biotinyllysine)1. Biocytin is biotin bound to the amino acid lysine.

Many foods contain some biotin. Foods that contain the most biotin include organ meats, eggs, fish, meat, seeds, nuts, and certain vegetables (such as sweet potatoes). The biotin content of food can vary; for example, plant variety and season can affect the biotin content of cereal grains, and certain processing techniques (e.g., canning) can reduce the biotin content of foods4.

Dietary avidin, a glycoprotein in raw egg whites, binds tightly to dietary biotin and prevents

biotin’s absorption in the gastrointestinal tract. Cooking denatures avidin, making it unable to interfere with biotin absorption.

Free biotin is believed to be highly absorbed. Before uptake, biocytin is acted on by the enzyme biotinidase, forming free biotin and lysine. Free biotin is then taken up into the enterocyte through the sodium-dependent multivitamin transporter (SMVT), as shown below1,2,4.

Figure 10.83 Free biotin is taken up into the enterocyte by the SMVT. Most biotin, like all water-soluble B vitamins, is excreted in the urine. For more information on biotin, see the Required Web Link below.

Required Web Link:Biotin Fact Sheet for Health Professionals

Subsections:

• 10.81 Biotin Functions
• 10.82 Biotin Deficiency & Toxicity

References & Links

• Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
• Said H, Mohammed Z. (2006) Intestinal absorption of water-soluble vitamins: An update. Curr Opin Gastroenterol 22(2): 140-146.
• Zempleni J, Wijeratne SSK, Hassan Y. (2009) Biotin. Biofactors 35(1): 36-46.
• Biotin Fact Sheet for Health Professionals – https://ods.od.nih.gov/factsheets/Biotin- HealthProfessional/#h3

Links

Biotin Fact Sheet for Health Professionals – https://ods.od.nih.gov/factsheets/Biotin- HealthProfessional/#h3

Biotin Functions

Biotin is an important cofactor for carboxylase enzymes. As the name sounds, these enzymes add carboxylic acid groups (-COOH) to whatever compound they act on. In fatty acid synthesis, biotin is required by the enzyme that forms malonyl CoA from acetyl-CoA, as shown below1.

Figure 10.811 The conversion of acetyl CoA to malonyl CoA in fatty acid synthesis requires biotin2

Another biotin-requiring carboxylase is one that converts pyruvate to oxaloacetate in gluconeogenesis1. In addition to these two functions, biotin is also important for the breakdown of the amino acids isoleucine, leucine, methionine, and threonine1.

Biotin is an effective treatment for brittle nail syndrome, but it has not been shown to improve healthy nails3. There is little evidence to suggest that biotin improves healthy hair as well4.

References & Links

• Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
• https://www.biochemden.com/biosynthesis-saturated-fatty-acids-notes/
• Scheinfeld N, Dahdah MJ, Scher R. (2007) Vitamins and minerals: their role in nail health and disease. J Drugs Dermatol. 6(8): 782-787.
• Famenini S, Goh C. (2014) Evidence for supplemental treatments in androgenetic alopecia. J Drugs Dermatol. 13(7): 809-812.

Biotin Deficiency & Toxicity

Biotin deficiency is very rare. Symptoms of biotin deficiency include1:

• Skin rash
• Hair loss
• Neurological Impairments

There are a couple of ways that a person could develop a deficiency in biotin. First, a very small number of people are born with a mutation in biotinidase that results in them not being able to process biocytin for absorption1. Another way is through the consumption of raw eggs. Drinking raw eggs is not something that most people do. However, some people do it to imitate Sylvester Stallone’s movie character Rocky, who consumed them as part of his boxing training regimen. If you are not familiar with this movie the link below shows you how Rocky consumed his raw eggs.

Required Web LinkVideo: Rocky Raw Eggs (1:21)

The potential problem with consuming raw eggs routinely is that raw egg whites contain a protein called avidin which binds biotin and prevents it from being absorbed. However, it would take more than two dozen egg whites consumed daily over many months to cause a

deficiency, making this an unlikely occurrence2. Cooking denatures avidin and prevents it from binding biotin, meaning that cooked eggs are not a concern.

No toxicity of biotin has been reported.

References & Links

• Byrd-Bredbenner C, Moe G, Beshgetoor D, Berning J. (2009) Wardlaw’s perspectives in nutrition. New York, NY: McGraw-Hill.
• Whitney E, Rolfes SR. (2008) Understanding nutrition. Belmont, CA: Thomson Wadsworth.

Videos

Rocky Raw Eggs – http://www.youtube.com/watch?v=NhkdLHSKo9s