Every now and then some vitamin or dietary supplement becomes all the rage.  A couple of generations ago vitamin C was the miracle drug that could prevent all diseases, despite lots of evidence to the contrary.  Lots of my patients still take it for colds, demonstrating its persistent mythology.  Vitamin B12 became the wonder-drug a few decades ago, leading to a whole generation of patients getting monthly injections for reasons that remain scientifically mysterious.  And many lesser stars can b...