Does low vitamin B12 cause hair loss?

In adults, the studies that looked for a link did not find one. A meta-analysis of 18 studies with 2,538 people who had weight-loss surgery found hair loss tied to low zinc, folate and ferritin, and not to vitamin B12. A case-control study of 91 people with diffuse hair loss and 74 controls found no difference in blood B12. The exception is infants with severe deficiency, whose hair becomes sparse or brittle and improves after treatment. No randomized trial has tested B12 for hair loss.

Unsettled. The adult evidence leans toward no link, and it is weak in both directions. Every adult study here is observational, most are small, and blood B12 is a poor guide to what the tissues have. In the surgery studies almost everyone took B12 routinely, which could hide a link that exists. What the data do not show is that a B12 shortfall is a common hidden cause of shedding in adults.

Percent of people with telogen effluvium found deficient, in two clinic record reviews

Neither clinic had a comparison group of people without hair loss, so these bars show how often a deficiency turned up, not whether it caused the shedding. Clinic B tested only some patients, and clinics use different cut-offs. No intervals are reported, so none is drawn. Sources: cards ev-b12h-06 and ev-b12h-07 below.

What the trials found

There is no hair trial

The one level A source on this page is a Cochrane review of 3 randomized trials in 153 adults with B12 deficiency, mean ages 38.6 to 72, treated for 3 to 4 months. Oral B12 at 1000 mcg a day normalized blood B12 with no clinically relevant difference from injections, on low quality evidence. At 2000 mcg a day the oral group ended 680 pg/mL higher than the injection group (95% CI 392.7 to 967.3). None of the three trials reported symptoms of deficiency, hair included. So the strongest evidence tells you how to fix a proven deficiency. It says nothing about what fixing it does to hair.

Adults with hair loss, compared with adults without

The surgery meta-analysis found hair loss in 57 percent of patients (95% CI 42 to 71). Lower folate (standardized difference -0.88, 95% CI -1.29 to -0.46) and lower ferritin (-0.22, 95% CI -0.38 to -0.05) went with it, and B12 did not. These are observational studies, and routine B12 after surgery may hide a link. A prospective cohort of 261 surgery patients, tested with a hair pull test at 0, 3 and 6 months, found the same pattern. Low iron was strongly tied to hair loss at 3 and 6 months, and zinc, folate and B12 showed no consistent link. Everyone in that cohort received B12, so it cannot test what a deficiency does.

Outside surgery, the Turkish case-control study of 91 patients and 74 controls found no difference in B12, folate or zinc. Most of the patients had telogen effluvium, the diffuse shedding that follows illness or stress, and the rest had pattern hair loss. It was small, from one center. For alopecia areata, the patchy autoimmune kind, a systematic review of micronutrients found 3 case-control studies, the largest with 75 patients and 54 controls. None found lower B12 in patients. Case reports of alopecia areata alongside pernicious anemia do exist.

How often deficiency turns up in hair clinics

Two record reviews from Turkish clinics give very different answers. In 2,851 women with telogen effluvium seen over 14 years, 5.8 percent had B12 deficiency, while 46.5 percent of those tested had low ferritin. In 3,028 patients at another center, 30.7 percent of those screened had low B12. Only some patients were screened there, cut-offs differ between clinics, and neither study had a group without hair loss to compare with. These numbers cannot say whether B12 had anything to do with the shedding.

Infants are the clear exception

In a case series of 43 Indian infants aged 4 to 27 months with B12 deficiency, all 43 had brown, sparse scalp hair. After treatment skin changes cleared in 3 to 4 weeks, and the hair was slower to recover. In 57 Turkish infants aged 6 to 24 months, 22.8 percent had brittle, dull hair, and three months after B12 injections it had improved in 92.3 percent of them. That study had no control group and recorded hair quality, not hair loss. Both describe severe deficiency in infancy, and the findings do not transfer to adults who notice more hair in the brush.

Who should be careful

The people most likely to run low on B12 are those taking certain medicines. The NIH notes that metformin and stomach acid blockers can lower B12 levels. In a meta-analysis of 31 studies, people with diabetes taking metformin had about twice the risk of B12 deficiency (relative risk 2.09, 95% CI 1.49 to 2.93), with blood B12 63.70 pM lower, and the gap depended on dose and duration. The heterogeneity was high, and none of those studies looked at hair.

The medicine that most clearly lowers vitamin B12, as a relative risk

Observational data

One meta-analysis of observational studies and trials, with high heterogeneity. It measured blood B12, not hair. Our card gives no baseline rate, so the relative risk cannot be turned into a count of people. Source: card ev-b12h-13 below.

Not for everyone. If you take metformin or an acid blocker long term, the NIH advice is to discuss your B12 status with a doctor. That is a reason to test, and a test result is a better basis for treatment than hair loss.

B12 itself has little known harm. The NIH sets no upper intake limit because its potential for toxicity is low, which means harm was not found and does not mean high doses help. A 2026 review found B12 supplements generally well tolerated, with rare reports of acne-like and allergic reactions that cannot be fully separated from reactions to other ingredients. The same review found no consistent benefit in people without deficiency. We have no card on B12 for hair in pregnancy or in children beyond the infant studies above, and that gap is not a sign of safety.

What expert bodies say

We found no dermatology body position on B12 and hair that we could check and put on a card. A narrative review of vitamins and minerals in hair loss concluded there is not enough data to recommend B12 supplements for telogen effluvium or pattern hair loss, even where a deficiency is found. The NIH Office of Dietary Supplements fact sheet has nothing on hair. It speaks to the upper limit and to the medicines above.

How we searched

Searched: a local copy of PubMed, queried on 6 October 2026 for vitamin B12, cobalamin or cyanocobalamin with hair loss, alopecia, telogen effluvium or hair (56 hits, none a relevant randomized trial). Further queries covered micronutrient reviews in alopecia (17 hits, none pooling B12 for hair), B12 and premature greying, oral against injected B12, metformin and B12, and acne-like reactions to B12. We also searched ClinicalTrials.gov (no registered trial on B12 and hair loss), the NIH Office of Dietary Supplements fact sheet (nothing on hair), the web for newer reviews, and Retraction Watch for every source used. None was retracted.

Included: the Cochrane review on treating deficiency, a meta-analysis of hair loss after surgery, a systematic review on alopecia areata, a prospective cohort, a case-control study, two clinic record reviews, two infant studies, a meta-analysis on metformin, two narrative reviews and two NIH passages, cited below.

Excluded: two recent meta-analyses of biomarkers and trace elements in alopecia areata that reported no B12 result. Two reviews of diet and hair that grouped the B vitamins without B12 figures. A review of premature greying, which is about color and not loss. Further clinic prevalence reports, case reports of hair color change, and trials where B12 was given to reduce chemotherapy side effects.

What we read: abstracts, with each quotation checked against the abstract text. For the alopecia areata review and the narrative review of vitamins in hair loss we read the full text.

What we could not get: a case-control study of B12 and holotranscobalamin in alopecia areata, which is not in our corpus and has no free full text. We cite its result through the two reviews that discuss it. A systematic review of supplements for hair loss in a dermatology journal, whose abstract does not name B12 and whose full text is paywalled.

What would change this answer

A randomized trial of B12 against placebo in adults with diffuse shedding and a measured B12 deficiency, with hair counts as the outcome. We found none, in print or registered.
A controlled study in people who are not given B12 routinely. The surgery data are the largest adult set, and routine supplementation may hide what a shortfall does.
Studies that measure B12 status with a better marker than blood B12, so that a missing link can be told apart from a poor test.

How much B12 you need, who runs short and where it comes from in food is in the vitamin B12 guide. Iron, which does track hair loss in the same surgery data, has its own evidence page.

The rest of the nutrient, in one place. Vitamin B12: who actually needs to worry, and why the damage can be permanent → What it does, how much you need, who runs short, and what too much does, with the evidence level shown on every line.

The full guide

Vitamin B12: who actually needs to worry, and why the damage can be permanent

The same question for other foods (hair loss)

Sources

ev-b12h-01 · Meta-analysis or systematic review · Cochrane systematic review of randomized controlled trials, no meta-analysis · n = 153
Low quality evidence shows oral and IM vitamin B12 having similar effects in terms of normalising serum vitamin B12 levels, but oral treatment costs less.
Who: adults with vitamin B12 deficiency, mean age 38.6 to 72 years, treated 3 to 4 months
Effect: 1000 ug/day oral: no clinically relevant difference in serum B12 vs IM; 2000 ug/day oral: MD +680 pg/mL (95% CI 392.7 to 967.3) vs IM
Certainty: Low quality evidence (GRADE) for serum B12; no trial reported clinical signs or symptoms of deficiency.
Cochrane Database Syst Rev, 2018 · checked 2026-10-06 · we read the abstract
ev-b12h-02 · Observational data · systematic review and meta-analysis of observational studies · n = 2,538
Serum zinc (standardized mean difference (SMD), - 1.13; 95% CI, - 2.27 to 0.01, p = 0.05), folic acid (SMD = - 0.88, 95% CI - 1.29 to - 0.46, p < 0.0001), and ferritin levels (SMD, - 0.22; 95% CI, - 0.38 to - 0.05; p = 0.01), but not serum iron and vitamin B12, were associated with hair loss following MBS.
Who: adults after metabolic and bariatric surgery
Effect: hair loss incidence 57% (95% CI 42 to 71%); folate SMD -0.88 (-1.29 to -0.46); ferritin SMD -0.22 (-0.38 to -0.05); vitamin B12 not associated
Certainty: Observational studies; routine B12 supplementation after surgery may hide any link.
Obes Surg, 2021 · checked 2026-10-06 · we read the abstract
ev-b12h-03 · Observational data · prospective comparative cohort · n = 261
Reduced iron levels were strongly associated with increased hair loss at both 3 and 6 months (p < 0.01), while zinc, folate, and vitamin B12 showed no consistent associations.
Who: patients after one-anastomosis gastric bypass (144) or sleeve gastrectomy (117), hair pull test at 0, 3 and 6 months
Effect: low iron strongly associated with hair loss at 3 and 6 months (p < 0.01); zinc, folate and B12 no consistent association; B12 rose with routine supplementation
Certainty: Everyone received routine B12, so the cohort cannot test what B12 deficiency does.
Obes Surg, 2026 · checked 2026-10-06 · we read the abstract
ev-b12h-04 · Observational data · case-control study · n = 165
There was no significant difference between the patients with alopecia and controls for zinc, folate and vitamin B(12) levels, or for psychological test scores.
Who: patients with diffuse hair loss (73.6% telogen effluvium, 26.4% androgenetic alopecia) and healthy controls
Effect: no significant difference in serum B12, folate or zinc vs controls
Certainty: Small, single center in Turkey; serum B12 is a weak marker of tissue status.
Clin Exp Dermatol, 2009 · checked 2026-10-06 · we read the abstract
ev-b12h-05 · Observational data · systematic literature review of observational studies and case reports · n = 3 case-control studies
available case-control studies [72, 79, 80] with multiple AA cases did not identify any such differences in B12 levels in patients compared to controls.
Who: patients with alopecia areata in case-control studies (largest 75 patients, 54 controls)
Effect: no difference in serum B12 or holotranscobalamin; red cell folate lower in one study
Certainty: Small case-control studies only; case reports of alopecia areata with pernicious anemia exist.
American Journal of Clinical Dermatology, 2017, The Role of Micronutrients in Alopecia Areata: A Review · checked 2026-10-06 · we read the fulltext
ev-b12h-06 · Observational data · single-center retrospective chart review · n = 2,851
Vitamin 12 deficiency was detected in 150 (5.8%), folic acid deficiency in 8 (0.6%), and iron deficiency in 685 (29.5%) patients.
Who: female patients with telogen effluvium, mean age 26.3 years, one dermatology clinic in Turkey
Effect: B12 deficiency 150 (5.8%); low ferritin 1,123 of 2,413 (46.5%); iron deficiency 29.5%; folate deficiency 0.6%
Certainty: No control group, so prevalence cannot be compared with women without hair loss.
J Cosmet Dermatol, 2025 · checked 2026-10-06 · we read the abstract
ev-b12h-07 · Observational data · single-center retrospective chart review · n = 3,028
In screened patients, vitamin and mineral deficiencies were as follows: vitamin D (72.2%), vitamin B12 (30.7%), folate (4.4%), and zinc (2.1%).
Who: patients with telogen effluvium, one center in Turkey, electronic records
Effect: deficiency among screened patients: vitamin D 72.2%, vitamin B12 30.7%, folate 4.4%, zinc 2.1%
Certainty: Only some patients were tested; no controls; cut-offs for deficiency differ between clinics.
J Cosmet Dermatol, 2022 · checked 2026-10-06 · we read the abstract
ev-b12h-08 · Observational data · case series (retrospective chart review) · n = 43
Skin pigmentation and mucosal changes resolved completely by 3-4 weeks, but hair changes were slower to reverse.
Who: infants aged 4 to 27 months with vitamin B12 deficiency, India
Effect: brown and sparse scalp hair in 43 of 43; skin pigmentation resolved in 3 to 4 weeks, hair slower
Certainty: Severe infant deficiency in a high-prevalence setting; not comparable with adult hair loss.
Pediatr Dermatol, 2018 · checked 2026-10-06 · we read the abstract
ev-b12h-09 · Observational data · prospective uncontrolled cohort · n = 57
Three months after the treatment initiation, hyperpigmentation improved in 87.75%, atrophic glossitis in 97.5% and brittle and matt hair in 92.3% of the patients.
Who: infants aged 6 to 24 months with vitamin B12 deficiency, treated with intramuscular cyanocobalamin, Turkey
Effect: brittle and matt hair 13 of 57 (22.8%); improved in 92.3% at 3 months
Certainty: No control group; hair quality, not hair loss, was recorded.
Cutan Ocul Toxicol, 2014 · checked 2026-10-06 · we read the abstract
ev-b12h-10 · Position of an expert body · narrative review · n = —
At the present time there is insufficient data to recommend zinc, riboflavin, folic acid, or vitamin B12 supplementation in cases of deficiency.
Who: people with androgenetic alopecia or telogen effluvium
Effect: no recommendation for B12 supplementation; same for folate, zinc and riboflavin
Certainty: Narrative review without a pooled analysis.
Dermatology and Therapy, 2019, The Role of Vitamins and Minerals in Hair Loss: A Review · checked 2026-10-06 · we read the fulltext
ev-b12h-11 · Position of an expert body · agency fact sheet · n = —
The FNB did not establish a UL for vitamin B12 because of its low potential for toxicity [1].
Who: general population, NIH Office of Dietary Supplements vitamin B12 fact sheet
Effect: no Tolerable Upper Intake Level set by the Food and Nutrition Board
Certainty: No UL does not mean high doses are useful; it means harm was not found.
NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-06 · we read the section
ev-b12h-12 · Position of an expert body · agency fact sheet · n = —
Vitamin B12 supplements may interact with medications, and some medications, including gastric acid inhibitors and metformin, may affect vitamin B12 levels.
Who: people taking gastric acid inhibitors or metformin regularly
Effect: medications may lower B12 levels; check status
Certainty: Agency summary; size of the effect is in the meta-analysis card.
NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals · checked 2026-10-06 · we read the section
ev-b12h-13 · Observational data · meta-analysis of observational studies and trials · n = 31 studies
Compared with diabetic patients not taking metformin, patients taking metformin had a significantly higher risk of vitamin B12 deficiency (RR 2.09; 95% CI 1.49, 2.93; P < 0.0001; I2 = 64%) and significantly lower serum vitamin B12 concentrations (MD -63.70; 95% CI -74.35, -53.05] pM; P < 0.00001; I2 = 87%), which depended on dose and duration of treatment.
Who: patients with diabetes taking or not taking metformin
Effect: B12 deficiency RR 2.09 (95% CI 1.49 to 2.93); serum B12 MD -63.70 pM (-74.35 to -53.05); depends on dose and duration
Certainty: High heterogeneity (I2 64% and 87%); no hair outcomes.
J Diabetes, 2019 · checked 2026-10-06 · we read the abstract
ev-b12h-14 · Position of an expert body · narrative review · n = —
There are rare reports of acneiform and hypersensitivity responses, although these cannot be completely distinguished from reactions to, e.g., excipients.
Who: people taking vitamin B12 supplements without proven deficiency
Effect: no consistent benefit without deficiency; rare acneiform and hypersensitivity reports
Certainty: Narrative review; reactions may be due to excipients rather than B12.
Nutrients, 2026 · checked 2026-10-06 · we read the abstract

How this page was made. Evidence was extracted from primary sources into cards, every number was re-checked against the source, and the text was written from those cards. Bioma Learn has no human medical reviewer at this time, and we say so rather than invent one. Methodology. This is information, not medical advice.