KN

KIN 343 - 11.26 Vitamin B7 Overview, DRIs and Sources

Vitamin B7 (Biotin) Overview

  • Biotin Overview

    • Also known as Vitamin B7.

    • Can be obtained from food and synthesized by intestinal bacteria.

    • Covalently bound to proteins or the amino acid lysine, forming a compound called biocitin.

Comparison with Niacin

  • Niacitin: Similar to biocitin; occurs when niacin is bound to carbohydrates, making it non-bioavailable.

  • Unlike niacitin, biocitin can be digested and absorbed, thanks to the enzyme biotinidase that separates lysine and biotin.

Dietary Reference Intakes (DRIs)

  • Adequate Intake (AI): Established due to variability in sourcing biotin

  • No Tolerable Upper Intake Levels (ULs) or toxicity have been documented.

  • Measured in micrograms per day (small amounts).

Age and Gender Variation

  • Infants to Adults: Required amounts increase with age, peaking in adulthood.

  • Pregnancy: Increased requirements compared to younger individuals; if pregnancy occurs in those over 18, the AI remains the same as for adults.

  • Lactation: Higher biotin requirement (an increase of 5 micrograms) due to breast milk being a good source of biotin.

Food Sources of Biotin

  • Wide variation in biotin levels among foods.

  • Sufficient AI can be obtained from:

    • One Egg: May provide the adequate intake.

    • One Hundred Grams of Liver: Also a good source.

    • Animal Products: Cheddar cheese and milk have lower biotin levels.

    • Plant Sources: Generally low in biotin.

Avidin and Biotin Interaction

  • Avidin: A protein in raw egg whites that binds to biotin very strongly.

    • Avidin-biotin complex is not absorbed, leading to potential biotin deficiency.

  • Impact of Cooking: Cooking egg whites denatures avidin, thereby allowing biotin to be absorbed.

  • Cultural Reference: In the 80s, portrayals of "tough guys" often included raw egg shakes promoting protein, leading to biotin deficiency due to avidin.

Digestion and Absorption of Biotin

  • Biotin from dietary sources is effectively absorbed when not bound to avidin.

  • The process begins in the digestive system, highlighting the importance of proper food preparation (i.e., cooking eggs) to maintain nutritional value.