What is the recommended dosage for Vitamin B12?

General: 2.4 mcg/day; Deficiency: 1,000-2,000 mcg/day

What are the side effects of Vitamin B12?

Potential side effects include: Generally well tolerated even at high doses, Rare allergic reactions (itching, swelling), Mild diarrhea or nausea at very high doses.

Does vitamin B12 help with hair loss?

Vitamin B12 is essential for red blood cell formation and oxygen delivery to hair follicles. Research suggests that B12 deficiency — common in vegetarians, vegans, and people with malabsorption conditions — may contribute to hair thinning. A 2019 review in Dermatology and Therapy noted associations between low B12 levels and diffuse hair loss. Supplementation may help when deficiency is confirmed.

What are the signs of vitamin B12 deficiency that affect hair?

Vitamin B12 deficiency may manifest as fatigue, pale skin, numbness, and diffuse hair thinning. Because B12 is crucial for DNA synthesis in rapidly dividing cells like hair follicles, prolonged deficiency may slow hair growth. Blood tests for serum B12 and methylmalonic acid can confirm deficiency status.

Why does vitamin B12 have negative evidence for hair loss on HairCited?

Vitamin B12 receives a Grade F (Negative) rating in both telogen effluvium and nutritional deficiency hair loss, based on 20 studies with 8,355 participants. While B12 deficiency can affect overall health and contribute to anemia that may secondarily impact hair, direct supplementation studies have not shown consistent positive effects on hair outcomes in populations without confirmed severe deficiency. This highlights the importance of targeted deficiency correction over routine supplementation.

Should I take vitamin B12 injections for hair loss?

Vitamin B12 injections are used to correct severe deficiency (such as in pernicious anemia or malabsorption), not as a general hair growth treatment. Research across 13 studies with 8,121 participants for telogen effluvium gives B12 a Grade F (Negative) rating — meaning supplementation does not improve hair outcomes at population level. If serum B12 levels are confirmed low, correcting deficiency is appropriate for overall health, but injections are unlikely to produce hair benefits in people with normal B12 levels.

How does vitamin B12 affect hair follicles?

Vitamin B12 is essential for DNA synthesis and red blood cell formation — both important for healthy follicle cell division during anagen. Severe B12 deficiency can cause megaloblastic anemia, which reduces oxygen delivery to follicles and may precipitate hair shedding. However, the research across 20 studies with 8,355 participants indicates that B12 supplementation does not significantly improve hair loss outcomes even in people with low-normal B12 levels, suggesting other factors are more critical for most hair loss presentations.

Vitamin B12

vitamin

Also known as: Cobalamin, Methylcobalamin, Cyanocobalamin

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About

Vitamin B12 is essential for red blood cell formation and DNA synthesis in rapidly dividing cells, including hair follicle keratinocytes. Deficiency can cause diffuse hair loss, premature graying, and is particularly common in vegans and individuals with pernicious anemia.

How It Works

Essential for red blood cell formation and DNA synthesis in rapidly dividing hair follicle cells.

Evidence For Conditions

Condition	Grade	Studies	Participants
Nutritional Deficiency Hair Loss	F	19	8130	View →
Telogen Effluvium	F	13	8121	View →

Side Effects

Generally well tolerated even at high doses
Rare allergic reactions (itching, swelling)
Mild diarrhea or nausea at very high doses

Drug & Supplement Interactions

Metformin (reduces B12 absorption by 10-30%)
Proton pump inhibitors and H2 blockers (reduce B12 absorption)
Colchicine (may reduce B12 absorption)

Always inform your healthcare provider about all supplements you take.

Related Ingredients

Biotin Folate Vitamin A Vitamin D Vitamin E

Quick Facts

Dosage: General: 2.4 mcg/day; Deficiency: 1,000-2,000 mcg/day
Forms: capsule tablet sublingual injection
Natural Sources: Meat, Fish, Dairy, Eggs, Fortified nutritional yeast
Upper Limit: No established UL
Best Time: With meals; sublingual form can be taken any time

Evidence Summary

Nutritional Deficiency Hair Loss F

Telogen Effluvium F

FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products and information on this website are not intended to diagnose, treat, cure, or prevent any disease. The evidence grades presented are based on our analysis of published peer-reviewed research and do not constitute medical advice. Always consult your healthcare provider before starting any supplement regimen.