What is the recommended dosage for Vitamin B12?

Vegans: 250-1,000 mcg/day; General: 2.4 mcg/day (RDA); Metformin Users: 1,000 mcg/day; Supplementation: 500-1,000 mcg/day methylcobalamin

What are the side effects of Vitamin B12?

Potential side effects include: Acne (rare, at high doses), Diarrhea (rare), Generally very well tolerated.

What is vitamin B12 and how may it relate to weight management?

Vitamin B12 (cobalamin) is essential for red blood cell formation, neurological function, and energy metabolism. B12 deficiency causes fatigue and weakness, which may impair exercise capacity. While B12 injections are marketed for weight loss, there is no strong clinical evidence that B12 supplementation promotes weight loss in non-deficient individuals.

What dosage of vitamin B12 is typically used in supplementation?

The RDA for vitamin B12 is 2.4 mcg per day for adults. Supplements commonly contain 500–5,000 mcg. Individuals at risk of deficiency include those over 50, vegans, vegetarians, and people with pernicious anemia or malabsorption. Both oral and sublingual forms are available; injections are used for severe deficiency.

What are the potential side effects of vitamin B12 supplements?

Oral vitamin B12 is generally very well tolerated, even at high doses, as excess is excreted in urine. Rare side effects include skin reactions and mild diarrhea. Injectable B12 may rarely cause injection site reactions. There is no established tolerable upper intake level for B12 due to its low toxicity potential.

Vitamin B12

vitamin_mineral

Also known as: Cobalamin, Methylcobalamin, Cyanocobalamin, Hydroxocobalamin, Adenosylcobalamin

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About

An essential cofactor for fatty acid metabolism and red blood cell formation. B12 deficiency — which is common in metformin users (10-30%) and vegans — impairs mitochondrial fatty acid oxidation and causes fatigue that limits physical activity. Benefits for weight management are primarily seen when correcting deficiency.

How It Works

Essential cofactor for methionine synthase (homocysteine remethylation) and methylmalonyl-CoA mutase (fatty acid and amino acid metabolism). B12 deficiency impairs mitochondrial fatty acid oxidation, leading to abnormal lipid accumulation. Also required for proper red blood cell formation — deficiency causes megaloblastic anemia with profound fatigue, reducing physical activity. Metformin depletes B12 in 10-30% of users.

Evidence For Conditions

Condition	Grade	Studies	Participants
Post-Bariatric Nutritional Support	B	10	1000	View →
Slow Metabolism	C	5	9000	View →

Side Effects

Acne (rare, at high doses)
Diarrhea (rare)
Generally very well tolerated

Drug & Supplement Interactions

Metformin (depletes B12 — monitor levels)
Proton pump inhibitors (reduced absorption)
H2 receptor antagonists (reduced absorption)
Colchicine (reduced absorption)

Always inform your healthcare provider about all supplements you take.

Related Ingredients

B-Complex Iron Magnesium Omega-3 Zinc

Quick Facts

Dosage: Vegans: 250-1,000 mcg/day; General: 2.4 mcg/day (RDA); Metformin_Users: 1,000 mcg/day; Supplementation: 500-1,000 mcg/day methylcobalamin
Forms: sublingual tablet capsule liquid injection (medical) nasal spray
Natural Sources: Liver, Clams, Sardines, Beef, Tuna, Fortified nutritional yeast, Fortified cereals
Upper Limit: No established UL (water-soluble, excess excreted)
Best Time: Morning (may provide energy boost); sublingual for better absorption; separate from vitamin C (

Evidence Summary

Post-Bariatric Nutritional Support B

Slow Metabolism C

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.