The mistake that most people make, with regards to nutrition and supplements, IS as Terry described, "A little knowledge is a dangerous thing..."
Most people probably SHOULD CONSULT a decent holistic nutritionist - or better yet, more than one - on the subjects of which nutritional supplements are best for their gender/age group/special needs...
Or at the very least, start reading reputable books and journals about it.
The mistake that Terry's dad made - taking huge doses of Vitamin C - apparently WITHOUT also supplementing calcium, zinc, vitamin D, vitamin K, and so on...
That is far too common. Vitamins work as part of a spectrum - not by themselves.
Why, one can SERIOUSLY muck up their health, if they begin taking only one or a few of the B-complex vitamins, WITHOUT taking the others...
Yeah, a little knowledge IS a dangerous thing...