Can too much vitamin B6 cause neuropathy or numbness?
Vitamin B6 supplements above 50 mg per day can cause nerve damage with long-term use. Stick to the recommended dose on the label and speak to your doctor if you develop tingling or numbness.
High doses of vitamin B6 from supplements can damage the nerves. This almost always affects the sensory nerves: people develop tingling, numbness or pain, especially in the hands and feet. Patients who stopped taking B6 reported that their symptoms improved, although recovery is not always fast or complete.
The threshold at which the risk increases is supplements above 50 mg per day, taken over a longer period. That is many times more than you get from food, so for most people a normal diet is not a risk factor. Multivitamins typically contain lower doses and have not been shown to be harmful in people who already have nerve complaints, as long as you stay within the officially permitted daily dose.
The reverse relationship, namely whether a deficiency of B6 can itself cause nerve damage, is less clear. Low B6 levels do occur in people with nerve problems, but it has not yet been proven that the deficiency is the direct cause.
Whether B6 supplements improve symptoms of existing nerve conditions has also not been established. Studies that reported improvement always used B6 in combination with other vitamins, which makes it impossible to isolate the effect of B6 on its own.
This answer is based on a combined summary of twenty studies and a literature review. The picture that high B6 causes harm is fairly consistent, but the available data on the precise dose threshold and recovery are limited. The researchers themselves note that the evidence is insufficient to recommend routine supplementation for nerve conditions.
Which form of folate reaches the brain most effectively?
In a folate transport disorder, folinic acid reaches the brain most effectively via alternative routes. For most people, the type of folate probably makes little difference for brain uptake.