From the Guidelines
Vitamin B6 toxicity can cause severe and potentially irreversible peripheral neuropathy, and individuals should avoid consuming high doses of this vitamin, typically exceeding 100 mg daily, to prevent such adverse effects. The primary symptoms of vitamin B6 toxicity include painful peripheral neuropathy, numbness, tingling, and burning sensations in the hands and feet, as well as difficulty walking, loss of balance, and reduced sensation to touch, vibration, and temperature 1. Other symptoms may include skin lesions, photosensitivity, nausea, heartburn, and in severe cases, seizures. The mechanism of toxicity involves direct damage to sensory neurons from pyridoxine's metabolites.
Key Findings
- A study published in Nutrition Research Reviews in 2018 found that peripheral neuropathy characterized by ultrastructural changes, including swelling of local mitochondria, disruption of axoplasmic ground substance, and accumulation of dense bodies within neurons, can occur due to vitamin B6 toxicity 1.
- The study also noted that motor neurons, particularly those feeding more distal muscles, appear most affected by this process, leading to an increasing denervation of muscle fibers.
- Another study published in Haematologica in 2010 highlighted the importance of cautious use of high doses of pyridoxine, especially in patients with renal insufficiency or low-protein diet, as it may induce lesions of the sensory neurons 1.
Recommendations
- Immediate discontinuation of vitamin B6 supplements is essential to prevent further damage and promote symptom improvement.
- People should avoid high-dose supplements unless prescribed by a healthcare provider and be cautious with multivitamins containing B6.
- Individuals with kidney disease, autoimmune disorders, or taking certain medications may have increased susceptibility to vitamin B6 toxicity and should be closely monitored.
- The recommended daily allowance for vitamin B6 is only 1.3-1.7 mg for adults, with a tolerable upper intake level of 100 mg daily.
Prevention and Management
- Regular clinical evaluation of symptoms and performance status is crucial to monitor clinical changes and prevent severe peripheral neuropathy.
- Patients experiencing neurological symptoms while taking supplements should report them promptly to their healthcare provider.
- Treatment options, such as pregabalin, gabapentin, or duloxetine, may be considered to manage chronic pain and other symptoms associated with vitamin B6 toxicity.
From the Research
Effects of Vitamin B6 Toxicity
- Vitamin B6 toxicity can occur due to excessive intake of supplements, typically at levels >100 nmol/L or 25 μg/L 2
- The effects of Vitamin B6 toxicity include:
- Peripheral neuropathy, which can present with symptoms such as paraesthesia, ataxia, and imbalance 3, 4, 5
- Sensory disturbances, including numbness, leg pain, and painful tingling 6
- Diffuse tremor in newborns, secondary to maternal intake of high doses of vitamin B6 during pregnancy and breastfeeding 4
- Gait disorders and motor and sensitive deficits 5
- The prognosis for Vitamin B6 toxicity is generally favorable, with symptoms improving once excessive vitamin B6 levels return to the physiological range 4
- Discontinuation of vitamin B6 supplements can lead to a decrease in vitamin B6 levels and improvement in symptoms 5, 6
Risk Factors for Vitamin B6 Toxicity
- Daily intake of high-dose vitamin B6 supplements, even at levels lower than the Tolerable Upper Intake Level (UL) of 12 mg/day 3
- Self-administration of over-the-counter vitamin-containing drugs 5
- Maternal intake of high doses of vitamin B6 during pregnancy and breastfeeding 4
Diagnosis and Prevention
- Plasma B6 levels should be ordered as part of the workup for any unexplained anemia or peripheral neuropathy 2
- Weekly administration of low-dose vitamin B6 supplements (50-100 mg) is preferred over daily use to prevent toxicity 2
- PLP-based supplements are preferred over pyridoxine supplements due to minimal neurotoxicity observed in neuronal cell viability tests 2