According to Dr. Lamm, one reason for the lax regulation and testing that surrounds supplements is that the kind of trials necessary to "prove" a given drug works are insanely expensive. The only way to justify the cost would be to obtain a patent, giving the producer the right to exclusive sales, but you can't just go out and patent vitamin D.
Of course, there have been large studies conducted on vitamins' effectiveness, but results can be hazy at best, contradictory at worst, and rarely, if ever, demonstrate a causal link between a positive outcome and a vitamin supplement.
The science of vitamins', well, inconclusiveness has been well established enough in the medical community that some researchers will pen articles with aggressive titles like, "Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements."
Health claims are enticing, and placebos are powerful
Pop quiz, hot shot: which is more comforting to believe? Taking an over-the-counter supplement will make you healthier, happier, and live longer? Or that decline, disease, and death will inevitably strike us all?