I have a few posts near the end of that thread with some good info about the effect of manganese on dopamine, and a brief review of the neurotoxicity.
To answer your question, I don't think there's enough data to say if 20mg for a long time is potentially harmful. If I were to guess, I'd say it's not going to have much neurotoxicity at that dose, but OTOH it's not impossible. Partly because of these concerns, and partly due to the potential for downregulation, I stopped using it every day. Now I'll take 20mg on days when I want a slight dopamine boost; maybe once a week?
You could try 20mg to see if it even has any effect for you, but personally I wouldn't be entirely comfortable supplementing more than 10mg every day.
Those other vitamins and minerals have threads here, that could probably give you better info than I can quickly. Our google search box is gone atm, but you can still use it by adding
site:imminst.org to a google search.
Or maybe Lefega (the author of that thread on SAS) will be able to give you a better summary of how those others can impact SA.
Edited by chrono, 11 August 2010 - 05:59 AM.