Oh and besides testosterone and other hormonal causes of hair loss, there are a lot of nutritional things. Basically healthy food seems to be key.
One thing, antacids with meals (including calcium/magnesium supplements) inhibit metal absorption--especially iron. Proton pump inhibitors may do the same. Iron and other metals are necessary for hair growth (in the usual steady small daily dose from healthy food). At the same time, too much iron or another metal will cause hair loss too. That's why I now think it's worth avoiding supplements and achieving nutrient balance only with healthy food... anything else should only be done with professional medical advice. (Following random supplement suggestions on the internet can ruin one's health--imagine that!)
Another nutritional thing: if the hair loss is stress or anxiety related, it may be due to mineral imbalance, in which case you may want to avoid calcium in excess if it could be. This is a dietary trick to decrease anxiety and lessen the physiological effects of stress. (I unknowingly had high calcium all through my youth from drinking too much milk.)
Processed foods keep increasing their levels of phosphate (because it has preservative value), but in excess, phosphate causes metal/mineral imbalance. That's one more reason I avoid or severely limit my consumption of most processed foods. (Tho honestly I don't know what benefit I notice from this.)
Taking any metal or mineral supplement or most vitamins (besides maybe a simple multivitamin) seems like an invitation to imbalance to me anymore (without qualified medical advice).