Biotin (Vitamin B7 / Vitamin H)

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Biotin, also known as Vitamin B7 or Vitamin H, is a water-soluble vitamin that plays a pivotal role in cellular metabolism, energy production, and maintenance of hair, skin, and nail health. Because the body cannot synthesize sufficient biotin on its own, it must be obtained through diet, gut bacterial production, or supplementation.

Functions in the Body

1. Metabolism of Macronutrients
   • Carbohydrate Metabolism: Acts as a coenzyme for pyruvate carboxylase, facilitating the conversion of pyruvate to oxaloacetate in gluconeogenesis.
   • Fat Metabolism: Serves as a cofactor for acetyl-CoA carboxylase, which catalyzes the rate-limiting step in fatty acid synthesis.
   • Protein Metabolism: Assists propionyl-CoA carboxylase and β-methylcrotonyl-CoA carboxylase, supporting amino acid catabolism and energy extraction.
2. Energy Production
   • By promoting gluconeogenesis, fatty acid synthesis, and amino acid breakdown, biotin ensures a steady supply of ATP (cellular energy) during fasting or increased energy demands.
3. Hair, Skin & Nail Health
   • Supports keratin infrastructure and cellular regeneration in the epidermis, hair follicles, and nail beds. Adequate biotin aids in maintaining strength, elasticity, and proper growth of these tissues.
4. Gene Regulation & Cell Signaling
   • Participates in histone biotinylation, a post-translational modification that influences chromatin structure and gene expression.
   • Plays a role in cellular signaling pathways tied to immune function and inflammation.

Symptoms of Deficiency

Although rare in well-nourished populations, biotin deficiency can occur in the following scenarios: prolonged raw egg white consumption (avidin binds biotin), genetic disorders affecting biotin recycling, total parenteral nutrition without supplementation, or long-term anticonvulsant therapy. Key features of deficiency include:

• Dermatologic Manifestations
  • Alopecia (Hair Loss): Diffuse thinning, hair fragility, or patchy hair loss.
  • Skin Rashes: Eczematous, scaly dermatitis—often periocular or periorificial.
• Nail Fragility
  • Brittle, ridged nails or delayed nail growth.
• Neurological & Psychological Signs
  • Depression, lethargy, hallucinations, paresthesia (numbness/tingling in hands and feet), ataxia (impaired coordination), and muscle pain.
• Metabolic Disturbances
  • Elevated blood lactate and an accumulation of organic acids (e.g., 3-hydroxyisovaleric acid).

Symptoms of Overdose (Hyperbiotinemia)

Because biotin is water-soluble, excess amounts are usually excreted in urine, and overt toxicity is exceedingly rare. However, very high supplemental doses—often >5,000 µg/day—may cause:

• Dermatologic Reactions
  • Mild skin rash or acneiform eruptions.
• Gastrointestinal Disturbances
  • Nausea, cramping, and mild diarrhea.
• Laboratory Interference
  • High biotin levels can falsely raise or lower certain immunoassay results (e.g., thyroid function tests, cardiac troponins), leading to misinterpretation.

Diagnosis

1. Plasma/Serum Biotin Level
   • Deficiency Threshold: Plasma biotin < 0.2 ng/mL (< 0.82 nmol/L) in fasting state suggests deficiency.
   • Adequate Range: 0.2–1.0 ng/mL (0.82–4.13 nmol/L).
   • Elevated Levels: > 2.0 ng/mL (8.27 nmol/L) may reflect high supplemental intake.
2. Urinary Biotin Excretion
   • Low 24-hour urinary biotin (< 9 µg/day) indicates inadequate intake or malabsorption.
3. Functional Markers
   • 3-Hydroxyisovaleric Acid (3-HIA): Elevated urinary 3-HIA suggests impaired biotin-dependent propionyl-CoA carboxylase activity.
   • Propionylcarnitine (C3) Accumulation: Detected on acylcarnitine profiling.
4. Clinical Examination
   • Evaluate hair/nail integrity, skin condition, and neurological signs consistent with biotin deficiency.

Dietary Sources

Food Source	Biotin Content (µg per Serving)
Beef Liver (3 oz, cooked)	30 µg
Egg Yolk (1 large, cooked)	10 µg
Salmon (3 oz, cooked)	5 µg
Almonds (½ cup)	1.5 µg
Peanuts (½ cup)	4.4 µg
Sunflower Seeds (2 Tbsp)	2.6 µg
Sweet Potato (1 medium)	2.4 µg
Spinach (½ cup, cooked)	0.5 µg
Broccoli (½ cup, cooked)	0.4 µg
Avocado (½ fruit)	2 µg
Whole-Grain Bread (1 slice)	0.5 µg
Cauliflower (½ cup, cooked)	0.2 µg

Recommended Daily Intake (RDI)

• Infants (0–6 months): 5 µg/day
• Infants (7–12 months): 6 µg/day
• Children (1–3 years): 8 µg/day
• Children (4–8 years): 12 µg/day
• Children & Adolescents (9–13 years): 20 µg/day
• Teens (14–18 years): 25 µg/day
• Adults (≥ 19 years): 30 µg/day
• Pregnant Women: 30 µg/day
• Lactating Women: 35 µg/day

Prevention & Maintenance

• Balanced Diet:
  Include biotin-rich foods daily, focusing on organ meats (if acceptable), eggs, nuts, seeds, and select vegetables. Overripe bananas and whole grains also contribute.
• Cooking Tips:
  • Prefer moderate cooking of eggs; excessive heat or prolonged boiling degrades biotin.
  • Store nuts and seeds in airtight containers to avoid rancidity (oxidative damage reduces biotin content).
• Malabsorption Considerations:
  • Individuals with gastrointestinal malabsorption (e.g., Crohn’s disease, celiac disease, or chronic antibiotic use) may need higher biotin intake or supplementation.
  • Monitor and correct gut dysbiosis, since colonic bacteria produce a portion of biotin.
• Supplementation Guidelines:
  • Consider 30 µg/day in healthy adults who have insufficient dietary intake.
  • For diagnosed deficiency, a therapeutic dose of 100–300 µg/day may be required under medical supervision.
  • Avoid megadoses (> 5,000 µg/day) without clear medical indication.

Frequently Asked Questions (FAQs)

1. What are the main benefits of biotin?
   • Biotin supports metabolism of carbohydrates, fats, and proteins; promotes healthy hair, skin, and nails; and is essential for energy production.
2. How do I know if I am deficient in biotin?
   • Key symptoms include hair loss, scaly rashes around the eyes or mouth, brittle nails, fatigue, depression, paresthesia, and elevated urinary 3-HIA levels.
   • Confirm with plasma biotin measurement (< 0.2 ng/mL) and urinary 3-HIA assay.
3. Can I get too much biotin?
   • Overdose is rare due to renal excretion. However, extremely high supplemental doses (> 5 mg/day) can cause mild skin rashes, gastrointestinal upset, and interfere with laboratory tests (e.g., thyroid panels, troponin assays).
4. What foods are particularly rich in biotin?
   • Organ meats (especially beef liver), egg yolks, nuts (almonds, peanuts), seeds (sunflower), salmon, whole grains, and certain vegetables (sweet potatoes, spinach).
5. Can biotin improve hair growth?
   • In people with biotin deficiency, supplementation (100–300 µg/day) often improves hair thickness and reduces hair shedding. In otherwise well-nourished individuals, evidence is limited, and hair improvement is less predictable.

Key Takeaways

• Critical Coenzyme: Biotin is indispensable for enzymatic reactions in gluconeogenesis, fatty acid synthesis, and amino acid catabolism.
• Deficiency Prevention: A varied diet including eggs, nuts, seeds, fish, and vegetables meets RDI in most healthy adults.
• Clinical Monitoring: Measure plasma biotin and urinary 3-HIA when deficiency is suspected—especially in malabsorption syndromes or with characteristic dermatologic and neurologic signs.
• Safe Supplementation: Use targeted supplemental doses under medical guidance; avoid unnecessary megadoses to prevent lab assay interference.
• Overall Health: Maintain gut health (since gut flora produce additional biotin), consume a balanced diet, and address underlying conditions (e.g., gastrointestinal disorders) to support optimal biotin status and metabolic health.

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