Fluoridated water? Thereby reducing one's purity of essence. (Sorry, couldn't help the Dr Strangelove reference.).
More seriously, ED can be a symptom for male diabetics. If you want to counter it, I would suggest that keeping good blood sugar control is the way to go.
Men tend to be a little shy about such things. I would strongly advise seeing a doctor for advice, since they have the knowledge and experience to help.