[hollerith]

If the situation was that everyone in the world could take 20 mg per day without problems, but then 21 mg per day would reliably cause irreversible damage, then yes as a society we would be very clear by now on the dangers of taking too much B6.

The actual situation is probably that most people can take 2 or 3 times 20 mg per day (and some people can take 10 times 20) without problems. There is a lot of variance in the gut absorption and the rate of metabolism of a lot of micronutrients in the human body.