The trouble with global rules as Kiwi posted.... is that there are medical conditions that doctors do not attend to, as Lara points out.

The foremost I see today in the medical literature is the DNA genetic error that impairs methylation. MTHFR polymorphisms.

These are more common than previously thought, and eating well will not fix this and the person will continue to decline.

Dr. Bruce Ames PhD has published that he believes that there are many undiscovered genetic flaws in metabolism of just the B complex vitamins. He published this before the MTHFR information became readily available.

Many of our vitamins come to us in food as INACTIVE forms.
Cobalamins
folic acid
pyridoxine (B6)
B5
B1
betacarotene (converts to Vit A)

These are the most common...and all require different enzyme systems to activate them in humans. Eating a good diet and having any one or more of these genetic errors will lead to
various deficiencies.

This is why some supplement makers are including the active forms of the above vitamins in their products.

In effect some people will starve in the midst of plenty and doctors and patients have no clue as to why.

And also people with inflamed GI tracts from Candida or pathological bacterial overgrowth, will also become malabsorbers and not even absorb the nutrients in the foods they consume.

So I really have a problem with those Government based statements of eat right and you won't need vitamins. Those comments are just not globally applicable to everyone equally.

Products like the one linked in the first post here are very dangerous. How in the world can the inert ingredients in it be labeled this way? Inert ingredients are added to products to increase their volume and make the manufacturing process easier and more accurate. They include flow enhancers like magnesium stearate, magnesium oxide, etc. In the inert category, should be a listing of what diluted the homeopathic ingredients...but of course, that is missing in the listing.

People might take such a product thinking they are getting B12 but since no dose is provided it may be a really pittance of a dose like 10mcg...and hence provide little if any benefit orally.
They would use this thinking they were doing "the right thing" since the price is high and suggests quality.

Everyone wanting to use supplements must learn about labeling and determining quality of products. This is essential to safety in using them, and success with benefits.