L-Histidine is an amino acid that the human body cannot manufacture, hence, it must be obtained from your diet, which is generally deficient, or from supplements which you can purchase
HISTIDINE (Non-Essential Amino Acid)
Are these two references in conflict? I’m not sure. I see that left and right handed moledcules could act quite differently, but I think we need to clarify before going further what the stated view is. This is a new area to me, so I’m learning as I read, and I just want to make sure I understand the position.