What I think is easily overlooked is the term "routine" in the following sentence: "Nutrition experts contend that all we need is what's typically found in a routine diet." Because routine is often defined as: "A prescribed, detailed course of action to be followed regularly; a standard procedure."
I suppose if we are all trained dietitians/nutritionists that should be easy-peasy, but for the vast majority of us?
Let us not forget simple facts like salt is iodized because most people would be deficient otherwise. Foods are often fortified and enriched because we would become nutrient deficient otherwise.
It also ignores niches within groups, such as this tidbit from WebMD: "... researchers found the most effect on people who were in extreme conditions, such as marathon runners. In this group, taking vitamin C cut their risk of catching a cold in half." Perhaps stressing the importance of exercise to achieve more optimal well-being. The NLM suggests people living in very cold temperatures also stand to benefit from vitamin C supplements, and I imagine that marathon running in a cold environment... better take some C!
Unfortunately, the studies, in general, are far from conclusive and in many cases present conflicting conclusions. Many studies also appear to ignore synergies between vitamins/minerals -- that groups often aid proper absorption and misgroupings can cause malabsorption or even leeching. For instance, I'd be interested in a study that compares EmergenC to 1 gram 'plain' vitamin C, because I'd imagine EmergenC is going to be more effective. Or maybe eating an orange or some fruit/veg with a certain amount of C VS just that amount of C by itself.
Like my momma always said, "where you going to find [insert practically any single vitamin/mineral] all by itself in nature that we actually eat?!" Even sea salt has lots of trace minerals! She was all about eating right FIRST and using supplements sparingly as backup (like Vit D in the winter months, to compensate for less sun on the skin). That's a great plan, IMO, but I doubt most people routinely do that.
"Love may fail, but courtesy will previal." -- A Kurt Vonnegut fan