NutraTalk Blog

Should You Be Concerned About B6 Toxicity?

Posted on : November 13, 2018 by Hardy Nutritionals® No Comments

Question from a customer:

"I am wondering why Hardy's uses the pyridoxine hydrochloride form of B6?  I work in mental health and would be so much more confident to recommend these products to people if I knew they were as safe as possible. As the science continues to evolve we now know that the old myth that water soluble vitamins can't hurt anyone is untrue."

 Daily Essential Nutrients (DEN) provides much less (70 milligrams of pyridoxine) at the full dose of 12 capsules per day and is considered safe for children and adults.

Vitamin B6 is the generic name for six compounds with vitamin B6 activity: pyridoxine, an alcohol; pyridoxal, an aldehyde; and pyridoxamine, which contains an amino group; and their respective 5’-phosphate esters. Pyridoxal 5’ phosphate (PLP) and pyridoxamine 5’ phosphate (PMP) are the active coenzyme forms of vitamin B6. Substantial proportions of the naturally occurring pyridoxine in fruits, vegetables, and grains exist in glycosylated forms that exhibit reduced bioavailability. [1]

What We Know About Vitamin B6 Metabolism

The human body absorbs vitamin B6 in the small intestine. Phosphorylated forms of the vitamin are dephosphorylated, and the pool of free vitamin B6 is absorbed by passive diffusion.

This means that in order to be absorbed the B6 molecule is reduced to a pyridoxine base first and is then re-phosphorylated after absorption.

Vitamin B6 is available in multivitamins, in supplements containing other B complex vitamins, and as a stand-alone supplement. The most common vitamin B6 form found in supplements is pyridoxine (in the form of pyridoxine hydrochloride [HCl]), although some supplements contain PLP (pyridoxal phosphate).  Absorption of vitamin B6 from supplements is similar to that from food sources and does not differ substantially among the various forms of supplements. Although the body absorbs large pharmacological doses of vitamin B6 well, it quickly eliminates most of the vitamin in the urine.

What We Know About Health Risks From Excessive Vitamin B6

Chronic administration of 1–6 grams oral pyridoxine per day for 12–40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control of bodily movements). Symptom severity appears to be dose dependent, and the symptoms usually stop if the patient discontinues the pyridoxine supplements as soon as the neurologic symptoms appear. Other effects of excessive vitamin B6 intakes include painful, disfiguring dermatological lesions; photosensitivity; and gastrointestinal symptoms, such as nausea and heartburn.

The FNB (Food and Nutrition Board) has established ULs (Upper Limits) for vitamin B6 that apply to both food and supplement intakes. The FNB noted that although several reports show sensory neuropathy occurring at doses lower than 500 mg/day, studies in patients treated with vitamin B6 (average dose of 200 mg/day) for up to 5 years found no evidence of this effect.

Sources: 

[1] https://ods.od.nih.gov/factsheets/VitaminB6-HealthProfessional/
Surtees R, Mills P, Clayton P. Inborn errors affecting vitamin B6
metabolism. Future Neurology.  2006 Sep; 1(5): 615-620.
https://www.futuremedicine.com/doi/10.2217/14796708.1.5.615

Footitt EJ, Clayton PT, Mills K, Heales SJ, Neergheen V, Oppenheim M, Mills
PB. Measurement of plasma B6 vitamer profiles in children with inborn errors
of vitamin B6 metabolism using an LC-MS/MS method.

J Inherit Metab Dis. 2013
Jan;36(1):139-45. doi: 10.1007/s10545-012-9493-y. Epub 2012 May 11. PubMed
PMID: 22576361.

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