High Quality Vitamin B12 Supplements

Vegans and vegetarians (B12 is only in animal products), older adults (absorption declines with age), people on metformin or PPIs (these reduce B12 absorption), and those with pernicious anemia or H. pylori. B12 deficiency causes fatigue, neuropathy, and cognitive issues.

Methylcobalamin is the active form, preferred for people with absorption or methylation issues. Cyanocobalamin is cheaper and well-studied — it converts to active forms in the body. For most people, either works. People with MTHFR variants or smokers may prefer methyl forms.

RDA is 2.4 mcg/day, but supplements typically provide 500–1,000 mcg because oral absorption is limited. Sublingual or injection forms bypass absorption issues. People with confirmed deficiency need higher loading doses initially.

Sublingual or oral high-dose B12 (1,000+ mcg/day) is as effective as injections for most people, including those with pernicious anemia, in clinical trials. Injections are useful for severe neurological deficiency or when oral absorption is severely impaired.

Fatigue, brain fog, peripheral neuropathy (tingling, numbness), pale skin, depression, balance issues, glossitis (smooth red tongue), and macrocytic anemia. Neurological damage from B12 deficiency can be permanent if not treated promptly.

Serum B12 is the standard test, but it has limitations. Methylmalonic acid (MMA) and homocysteine are more sensitive markers — they rise when B12 is functionally low even if serum looks normal. Test all three for a complete picture.

Metformin reduces B12 absorption by 10–30% over time. About 6–10% of long-term metformin users develop deficiency. Anyone on metformin for more than 2 years should test B12 annually and supplement if levels are low or borderline.

Animal sources only — clams, beef liver, sardines, tuna, salmon, beef, eggs, dairy, and fortified nutritional yeast. Plants don't contain reliable B12, which is why all vegans and most vegetarians need to supplement.

B12 has a strong safety record — no upper limit established. The body excretes excess in urine. Rare reactions include acne (mostly with high-dose cyanocobalamin) and rare hypersensitivity. Don't take huge doses without need.