Vitamin B6 and Hair: The Cysteine Connection Behind Keratin, and How Little Clinical Data Exists

Watch: Vitamin B6 and Hair — video

By Jack Zheng, MS Pharmacy — Founder of MIHIYO Labs

Summary

Vitamin B6 is a cofactor in the pathway that turns homocysteine into cysteine, the amino acid behind the disulfide bonds in hair keratin, but clinical evidence that taking B6 changes hair is very thin. The human hair evidence I identified is a small study of 46 women given B6 injections, whose abstract describes no placebo-controlled comparison. In 2012, the European Food Safety Authority concluded that a cause-and-effect relationship had not been established between a B-vitamin combination including pyridoxine and normal hair. Long-term high B6 intake is linked to peripheral neuropathy. MIHIYO Labs includes B6 in its 10-in-1 hair oral dissolving strip (ODS) for formula completeness, not as a hair-growth ingredient.

MIHIYO Labs' 10-in-1 Hair Growth Strip contains vitamin B6 as one of ten ingredients. Where it fits in that formula, and what we do not claim for it, is explained further down.

Does vitamin B6 help hair grow?

There is no good clinical evidence that taking vitamin B6 makes hair grow faster or reduces shedding in people who are not deficient.

The mechanism is real: B6 helps the body make cysteine, and cysteine is part of what holds hair keratin together. But a plausible pathway is not the same as a demonstrated effect on hair, and for B6 the gap between the two is wide. A 2019 review of vitamins and minerals in hair loss put it plainly: "Only riboflavin, biotin, folate, and vitamin B12 deficiencies have been associated with hair loss."⁷ Vitamin B6 was not among the deficiencies identified as associated with hair loss in that review. This reflects the limited evidence available, rather than proof that B6 deficiency can never affect hair.

This is the sixth article in a 20-part series on the ten ingredients in our hair formula, after vitamin B12, vitamin D, zinc, silica and who actually runs low on biotin.

What does vitamin B6 do in the body?

Vitamin B6 works through its coenzyme forms, mainly pyridoxal 5'-phosphate (PLP), in more than 100 enzyme reactions, most of them in protein metabolism.¹

Those reactions include keeping homocysteine, an amino acid in the blood, at normal levels.¹ Homocysteine sits at a fork in methionine metabolism:

• Remethylation turns homocysteine back into methionine. That step needs folate and vitamin B12.²
• Transsulfuration turns homocysteine into cysteine, with vitamin B6 as the cofactor.²

Cysteine matters for hair because two cysteines can join into cystine through a disulfide bond, and those bonds are what a permanent wave has to break to reshape hair.³ So B6 sits upstream of one of the raw materials hair is built from.

I would stop the chain there. Cysteine is used throughout the body, and nothing in this pathway shows that extra B6, in someone who already has enough, sends more cysteine into hair or changes how it grows.

What human evidence links B6 to hair?

The human evidence I identified includes a small study of 46 women with diffuse hair loss, examining intramuscular vitamin B6 and oral calcium pantothenate. The available English abstract describes before-and-after assessments but does not establish a placebo-controlled comparison.⁴

Brzezińska-Wcisło, a dermatologist in Katowice, Poland, studied 46 women from puberty to age 30 with diffuse hair loss. The abstract describes vitamin B6 by intramuscular injection every day for 20 to 30 days, repeated after six months, and calcium pantothenate (vitamin B5) by mouth, 100 mg twice a day, for four to five months, but it does not say how participants were allocated between the two treatments. Hair was assessed clinically and by trichogram before and after treatment.⁴

According to the English abstract, injected B6 improved hair condition "in a number of women" and reduced hair loss, especially in telogen-type shedding. Oral calcium pantothenate "did not show clearly the positive effect."⁴ The paper is in Polish and I could only read the abstract, which does not give the B6 dose, the number of women who improved, or any statistics.

What this cannot tell you:

• Whether the observed improvement was attributable to vitamin B6 rather than other factors, including the natural course of hair shedding. The abstract does not provide enough information about the treatment groups to isolate the effect of B6, and it describes no control group.
• Anything about oral B6. Injections bypass the gut, so the result does not transfer to a tablet or a strip.
• Anything about people who were not shedding, or whose B6 status was normal. The abstract does not report baseline B6 levels.

What about the laboratory study?

A 2022 laboratory study found that a combination including pyridoxine lengthened hair shafts in cultured mouse whisker follicles, but it did not test B6 alone or in people.⁵

Hu and colleagues, at the Japanese company ROHTO Pharmaceutical and Kyorin University, cultured mouse vibrissa (whisker) follicles with a combination of panthenyl ethyl ether, tocopherol acetate and pyridoxine, three vitamin derivatives used in topical hair products. The combination significantly promoted hair shaft elongation and increased hair matrix cell proliferation 1.9-fold compared with controls, through a growth-factor signal called PlGF. It also increased PlGF secretion in cultured human dermal papilla cells.⁵

Three things limit what this means for a supplement. It was organ and cell culture, not a person. It was a three-ingredient combination, so pyridoxine's own contribution cannot be separated. And it was designed around topical hair-care products, not oral intake.⁵ It is a reason for more research, not evidence that oral B6 grows hair.

What did European regulators conclude?

In 2012, the European Food Safety Authority (EFSA) concluded that "a cause and effect relationship has not been established" between a B-vitamin combination including pyridoxine and maintenance of normal hair.⁶

The application, from a company called Nutrilinks, covered a combination of thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, D-biotin and pumpkin seed oil, with the claimed effects "contributes to reduce hair loss" and "increases the number of hair" in healthy adults. The applicant identified one publication as pertinent, and that study did not use the combination in question, so EFSA could draw no conclusions from it.⁶

That opinion was about one specific combination and one submitted study. It does not prove B6 has no effect on hair. It does show that when a B-vitamin hair claim was put to a regulator with the evidence the applicant chose, the evidence was not there.

The B6 and hair evidence, side by side

Why does the dose of B6 matter so much?

Vitamin B6 has a well-established harm at high intakes: peripheral neuropathy, a form of nerve damage.⁸

In 2023, EFSA set the tolerable upper intake level for adults, including pregnant and breastfeeding women, at 12 mg a day.⁸ EFSA derived an upper limit of 12.5 mg a day from human evidence, using a reference point of 50 mg a day from a case-control study, supported by case reports and vigilance data, and an uncertainty factor of 4, chosen partly because time to symptoms gets shorter as the dose rises. An independent calculation based on animal data, from a study in beagle dogs, yielded 11.7 mg a day. EFSA considered both estimates and established a rounded adult upper limit of 12 mg a day.⁸ EFSA noted that EU populations are unlikely to exceed the limit except regular users of food supplements containing high doses of B6.⁸

The U.S. Food and Nutrition Board, earlier, set the adult upper limit at 100 mg a day.¹ The two bodies used different data and methods, so the gap reflects how each weighed the evidence, not a simple error on one side. Both are tolerable upper intake levels for total daily intake from food, fortified products and supplements together, not recommended daily doses or universal supplement-label limits.¹⁸ The NIH fact sheet notes that chronic intakes of 1 to 6 g a day for 12 to 40 months can cause severe, progressive sensory neuropathy.¹ Neurologic symptoms often improve or stop progressing after pyridoxine supplementation is discontinued, particularly when it is stopped promptly.¹ However, recovery may be prolonged or incomplete in some cases: among the case reports EFSA reviewed, one patient's symptoms improved only mildly three months after stopping, and motor weakness persisted.⁸ For comparison, the recommended intake for adults aged 19 to 50 is 1.3 mg a day.¹

This is why I care more about where B6 is coming from than about adding more of it. A multivitamin, a B-complex and a hair product can each contain B6, so taking them together adds up. I wrote about adding up overlapping ingredients in supplement stacking safety. If you notice nerve symptoms, such as numbness, tingling or unsteadiness, while taking B6-containing supplements, stop them and see a doctor.

Can B6 deficiency cause hair loss?

Hair loss is not among the signs of B6 deficiency listed by the NIH, and isolated B6 deficiency is uncommon.¹

The NIH fact sheet associates B6 deficiency with microcytic anemia, dermatitis with cheilosis (scaling on the lips and cracks at the corners of the mouth), glossitis (a swollen tongue), depression, confusion and weakened immune function.¹ It also notes that inadequate B6 status usually comes with low levels of other B vitamins, such as B12 and folic acid.¹ So if someone with shedding turns out to be low in B6, the more useful question is what else is low, and why.

Where this fits in MIHIYO Labs' 10-in-1 strip

MIHIYO Labs' 10-in-1 Hair Growth Strip combines 5,000 mcg biotin with zinc, copper, vitamin D3, B5, B6, B12, folate, bamboo silica and apple procyanidin B2. I group those ten ingredients by job rather than as one "stack", and explained in ingredient synergy why I do not use the word synergy for them.

Vitamin B6 sits in the coenzyme group, alongside biotin and B5, which support normal metabolic processes. Its formulation reason is completeness: the strip contains B6, B12 and folate together, so the cofactors for both branches of homocysteine metabolism are present, B12 and folate for remethylation and B6 for transsulfuration.² That is an argument about how the formula is put together, not evidence that the MIHIYO Labs hair strip improves hair. It has not been tested in a clinical trial.

The evidence grade I give B6 for hair is "biochemical rationale; one small injection study in people with no placebo-controlled comparison described; laboratory data only for a combination; a regulatory opinion that a B-vitamin hair claim was not substantiated". The strip is a nutritional formula, not a treatment for hair loss, and it contains no iron. Because B6 has a real upper limit, count it across every supplement you take.

Because the strip contains 5,000 mcg of biotin, tell your doctor you take a biotin-containing supplement before any blood test. The NIH notes that biotin taken beyond recommended intakes can cause clinically significant falsely high or falsely low laboratory test results.⁹ I cover which tests are affected in biotin and blood tests.

What are the honest limits of the B6 and hair evidence?

The biochemical pathway from B6 to cysteine is well established, but controlled human evidence has not demonstrated that additional B6 supplementation improves hair growth or reduces shedding.

• The human hair data come from a 46-woman study that used injections, with no placebo-controlled comparison described in its abstract; it was reported in Polish, and I could read only the abstract.⁴
• The laboratory data come from mouse follicles and a three-ingredient combination from a company that makes hair-care products.⁵
• The one regulatory review of a B-vitamin hair claim found the evidence insufficient.⁶
• I found no placebo-controlled trial of oral B6 alone for hair.
• None of this addresses hair loss with a medical cause, such as iron deficiency, thyroid disease or pattern hair loss.

Practical takeaways

• Do not take extra B6 to grow hair. There is no good clinical evidence that it does.
• Consider your total daily vitamin B6 intake from food, fortified products and supplements. The EFSA adult upper limit is 12 mg a day, while the U.S. Food and Nutrition Board established an adult upper limit of 100 mg a day. These are tolerable upper intake levels, not recommended daily doses or universal supplement-label limits.
• Numbness, tingling or unsteadiness while taking B6-containing supplements is a reason to stop them and see a doctor.
• Persistent shedding deserves a look for the common causes first; a dermatologist can work out which applies.
• If your hair supplement contains biotin, tell your doctor before any blood test.
• That is the role MIHIYO Labs gives B6 in its 10-in-1 strip: a cofactor included for completeness, with no hair-growth claim.

Frequently asked questions

Does vitamin B6 help hair growth?

There is no good clinical evidence that it does. B6 is a cofactor in making cysteine, which hair keratin uses, but the human hair data come from one small study of B6 injections in 46 women with no placebo-controlled comparison described, and EFSA found a cause-and-effect relationship had not been established for a B-vitamin hair claim.

Can vitamin B6 deficiency cause hair loss?

Hair loss is not among the signs of B6 deficiency listed by the NIH, which include anemia, cracked lips and a swollen tongue. Isolated B6 deficiency is uncommon and usually comes with low B12 and folate.

How much vitamin B6 is too much?

EFSA set the adult tolerable upper intake level at 12 mg a day in 2023; the U.S. Food and Nutrition Board's is 100 mg a day. Both apply to total daily intake from food, fortified products and supplements, and neither is a recommended dose. Long-term high intake is linked to peripheral neuropathy.

Does a B-complex help hair loss?

A B-complex may be helpful when a clinically relevant B-vitamin deficiency contributes to hair loss. However, identifying a deficiency does not guarantee that supplementation will restore hair growth. Evidence does not support routine B-complex supplementation for hair growth in people with adequate nutritional status, and a 2012 EFSA review of a B-vitamin combination found its hair claim was not substantiated.⁶

References

1. National Institutes of Health, Office of Dietary Supplements. Vitamin B6: Fact Sheet for Health Professionals. Updated June 16, 2023. https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/
2. González-Lamuño D, Arrieta-Blanco FJ, Fuentes ED, Forga-Visa MT, Morales-Conejo M, Peña-Quintana L, Vitoria-Miñana I. Hyperhomocysteinemia in Adult Patients: A Treatable Metabolic Condition. Nutrients. 2023;16(1):135. PMID: 38201964 / DOI: 10.3390/nu16010135. https://pubmed.ncbi.nlm.nih.gov/38201964/
3. Evans T. A Review of Permanent Waving and Perm Chemistry. Journal of Cosmetic Science. 2021;72(1):99-133. PMID: 35349429. https://pubmed.ncbi.nlm.nih.gov/35349429/
4. Brzezińska-Wcisło L. Evaluation of vitamin B6 and calcium pantothenate effectiveness on hair growth from clinical and trichographic aspects for treatment of diffuse alopecia in women [article in Polish]. Wiadomości Lekarskie. 2001;54(1-2):11-18. PMID: 11344694. https://pubmed.ncbi.nlm.nih.gov/11344694/
5. Hu L, Kimura S, Haga M, Kashiwagi S, Takagi K, Shimizu T, Ishii T, Ohyama M. Vitamins and their derivatives synergistically promote hair shaft elongation ex vivo via PlGF/VEGFR-1 signalling activation. Journal of Dermatological Science. 2022;108(1):2-11. PMID: 36210234 / DOI: 10.1016/j.jdermsci.2022.09.003. https://pubmed.ncbi.nlm.nih.gov/36210234/
6. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the substantiation of a health claim related to a combination of thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, D-biotin and pumpkin seed oil and maintenance of normal hair pursuant to Article 13(5) of Regulation (EC) No 1924/2006. EFSA Journal. 2012;10(7):2807. PMID: 42016079 / DOI: 10.2903/j.efsa.2012.2807. https://pubmed.ncbi.nlm.nih.gov/42016079/
7. Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatology and Therapy (Heidelberg). 2019;9(1):51-70. PMID: 30547302 / DOI: 10.1007/s13555-018-0278-6. https://pubmed.ncbi.nlm.nih.gov/30547302/
8. EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA). Scientific opinion on the tolerable upper intake level for vitamin B6. EFSA Journal. 2023;21(5):e08006. PMID: 37207271 / DOI: 10.2903/j.efsa.2023.8006. https://pubmed.ncbi.nlm.nih.gov/37207271/
9. National Institutes of Health, Office of Dietary Supplements. Biotin: Fact Sheet for Health Professionals. Updated January 10, 2022. https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/

By Jack Zheng, MS Pharmacy — Founder of MIHIYO Labs. Focused on the R&D of high-bioavailability, fast-absorption oral dissolving strips.