I am a doctor and the answer to that is a bit complicated. There is a great deal of teaching of biology, physiology and pathology in medical school. There is some quite limited amount specifically about nutrition and supplements etc. The main reason for skepticism from most physicians when it comes to claims about nutrition or supplements has to do with lack of evidence. Physicians, particularly in the last twenty years, have been extensively taught in the scientific method and in the assessment and need for clinical evidence. We have also seen many examples of drugs that "made sense" from a basic science reasoning approach or from animal studies but utterly failed in human trials. The fact is that there have been VERY few randomized controlled trials of nutritional products or diets and most of these have been negative. Many widely held beliefs about vitamins (Vit C for common cold is one example, Vitamin E for heart disease is another) just did not hold up to clinical trial evidence. A few "non trendy" vitamin examples actually made tremendous differences: folic acid supplementation for example has a big benefit in preventing neural tube defects (nasty birth defects including spina bifida) if given to women of childbearing age.
The other thing is that I believe it's a myth to think that somehow our diet is missing some magical vitamins and that supplements are a solution. Vitamins are usually "permissive" for physiology - you need a minimum amount of most and more isn't any better. Vitamin C is really important if you have NONE - scurvy was a huge killer in previous centuries, that doesn't mean that more is better. If you think about it we evolved over thousands of years with a vastly more restricted diet than now available. Even our parents generation marvel at the fresh produce and relative cheapness of food available to us. Much food is supplemented for certain vitamins that used to cause issues if deficient (Vit D in milk, iodine in salt for example). Our problem is too much food, not too little vitamins. There are exceptions obviously (Vegans need to be careful about protein and iron for example) but the evidence that most people need vitamin supplementation is fairly weak.
So if someone comes to me with claims about this or that, I am usually fairly skeptical. I'd like to see real evidence (not anecdotes, rationale or claims). I also let them know that excesses of some vitamins (iron for example) and normal doses of many herbal products can cause harm.
Just my opinion, I could be wrong.