I wondered whether it has to do with the valency of copper. Remember the story with Erin Brockovich about ground water contamination of chromium, a movie was made about the journalist that went after the chemical industry. It was the hexavalent chromium (Cr +6) that made it so toxic. Now I found an article about the toxicity of copper (II) (Cu+2)! So while there could be a deficiency in copper, at the same time the wrong type of copper can do harm!On the other hand, copper is deficient in Alzheimer's...
Evidence for widespread, severe brain copper deficiency in Alzheimer's dementia - PubMed
Datasets comprising simultaneous measurements of many essential metals in Alzheimer's disease (AD) brain are sparse, and available studies are not entirely in agreement. To further elucidate this matter, we employed inductively-coupled-plasma mass spectrometry to measure post-mortem levels of 8...pubmed.ncbi.nlm.nih.gov
Copper oxide and copper fluoride could both have +1 or +2 valency. So one has to find the right copper supplement where the valence is only +1 (Copper (I))!