From the Guidelines
A vitamin B6 level of 30.9 mcg/L is within the normal reference range, indicating adequate vitamin B6 status in the body, and no supplementation is necessary at this level. Vitamin B6 (pyridoxine) is essential for various physiological processes, including amino acid metabolism, as the cofactor pyridoxal 5′-phosphate (PLP) is involved in the synthesis of haeme, several neurotransmitters, purines, hormones, and fatty acids 1. The current level suggests sufficient dietary intake, likely from foods such as poultry, fish, potatoes, chickpeas, and bananas. Maintaining a balanced diet should continue to provide adequate vitamin B6. Some key points to consider:
- Vitamin B6 deficiency can manifest as a diverse symptom-set, affecting multiple systems, but a level of 30.9 mcg/L does not indicate deficiency 1.
- The biologically active form of vitamin B6, pyridoxal phosphate (PLP), serves as a coenzyme for more than 160 enzymatic reactions, including transaminations, racemizations, decarboxylations, and aldol cleavage 1.
- If medications that may interfere with B6 metabolism are being taken (such as isoniazid, penicillamine, or certain anticonvulsants), regular monitoring of vitamin B6 levels might be beneficial.
- Excessive supplementation beyond needs should be avoided, as very high levels (typically above 100 mcg/L) can potentially cause nerve damage over time.
From the Research
Vitamin B6 Levels and Neurotoxicity
- A plasma PLP concentration above 30 nmol/L (7.4 μg/L) is indicative of an adequate vitamin B6 status for all age and sex groups 2.
- PLP-based supplements are preferred and should be administered weekly in low doses (50-100 mg) to maintain a stable serum PLP level between 30 and 60 nmol/L or 7.4 and 15 μg/L 2.
- When B6 is administered daily in supraphysiologic doses, there is a potential for the development of neurotoxicity (typically at levels >100 nmol/L or 25 μg/L) 2.
Relationship Between Vitamin B6 and Peripheral Neuropathy
- Higher vitamin B6 levels, which usually occur following the taking of nutritional supplements, may lead to the development of a predominantly, if not exclusively, sensory neuropathy of the axonal type 3.
- Although low vitamin B6 levels can be seen in patients suffering from peripheral neuropathy of various etiologies, there is no firm evidence that low B6 levels have a direct causal relationship with PN 3.
- Current scientific evidence supports a neurotoxic role of B6 at high levels 3.
Vitamin B6 Levels and Neuropathy Severity
- Plasma B6 level was not related to neuropathy severity in a well-characterized cohort of patients with chronic idiopathic axonal polyneuropathy (CIAP) 4.
- Moderately elevated plasma B6 levels, even in the 100 to 200 μg/L range, are not associated with significantly worse neuropathy signs or symptoms 4.
Vitamin B6 Supplementation and Neuropathy
- Supplementation with vitamin B6, even as part of a nutritional multivitamin supplement, has not been proven harmful at permitted daily doses in patients who already suffer from PN 3.
- Causality assessment of the case series of 90 reports shows it is plausible for the vitamin B6 supplements to have caused complaints such as neuropathies, especially with higher dosages and prolonged use 5.