Vitamin B6 toxicity is known to be a cause of peripheral neuropathy. There is debate regarding the threshold at which intake levels can cause neurological symptoms through vitamin B6.
In a 2021 study from the Peripheral Neuropathy Research Registry (PNRR), funded by the Foundation for Peripheral Neuropathy, researchers asked if elevated plasma vitamin B6 levels were related to outcome measures in a well-characterized cohort of patients with chronic idiopathic axonal polyneuropathy (CIAP). It was concluded that vitamin B6 levels do not correlate with the severity of neuropathy.
The study included 261 patients enrolled in the Peripheral Neuropathy Research Registry who presented information regarding their plasma Vitamin B6 value. The study excluded patients with vitamin B6 deficiency (0-4.9 μg/L).
Researchers performed a chi-square test for independence. They then analyzed the logistic relation of elevated plasma B6 level to nerve conduction studies (NCS), neurological examination findings, and patient-reported symptoms. The patient’s age and time since neuropathy symptom onset were considered.
Plasma B6 level was not related to neuropathy severity. There was no logistic relation of elevated plasma B6 level to NCS results. Analysis included toe strength, vibration sense, and deep tendon reflexes, or patient-reported numbness or pain intensity. This study suggests that moderately elevated plasma B6 levels, even in the 100 to 200 μg/L range, are not associated with significantly worse neuropathy signs or symptoms. Although standard supplementation of B6 does not appear to have a major negative effect on CIAP, this study does not directly answer whether stopping supplementation will have a beneficial effect.
Very few patients in the study had vitamin B6 levels >300 μg/L, suggesting that screening for vitamin B6 toxicity may be left to the discretion of the physician.
Researchers interested in the PNRR data can find more information here.