Can Vitamin B12 Cause Hair Loss? What Studies Really Say

Many people are confused about B12 and hair: can vitamin B12 cause hair loss, or does it actually prevent it? The honest answer is that both very low and, in rare cases, very high B12 levels may be linked to shedding, but the strongest evidence points to deficiency as the real concern, not normal supplements.

How Vitamin B12 Affects Your Hair

Vitamin B12 helps your body make red blood cells, DNA, and new cells, including fast‑growing hair follicle cells. When B12 is low, fewer healthy red blood cells are made, so the scalp gets less oxygen and nutrients, and more hairs shift into the shedding (telogen) phase. Several clinical reports link B12 deficiency with diffuse thinning, chronic telogen effluvium, and even premature greying in some people.

So, Can Vitamin B12 Cause Hair Loss?

• B12 deficiency and hair loss: Stronger evidence. Case–control studies show a higher rate of B12 deficiency in people with chronic telogen effluvium compared with controls, and hair often improves after correcting the deficiency.
• Normal B12 intake: A review of vitamins and hair found that simply lowering B12 within normal ranges did not worsen shedding or growth in treated patients.
• Too much B12: A few guides mention excessive B12 as a possible hair loss trigger, but direct human data is limited; over‑supplementation in general is more clearly linked to problems with vitamin A or selenium than B12.

In simple terms, low B12 is a proven risk, high B12 is a theoretical one, and normal, doctor‑guided doses are usually safe for hair.

Vitamin B12 and Hair Loss at a Glance

When to Test and What to Do

Consider a B12 test if you have hair loss plus fatigue, pins‑and‑needles, low mood, tongue soreness, or a vegan/vegetarian diet, gut issues, or long‑term acid‑suppressing or metformin use. Work with a doctor on blood tests (B12, full blood count, sometimes methylmalonic acid) and only then add injections or tablets if truly deficient.

For most people, a balanced diet with eggs, dairy, fish, or fortified foods—and targeted supplements when needed—helps keep B12 in the “sweet spot” where it supports hair instead of harming it.