Since the nutritional supplement industry is unregulated by the FDA, none of the manyfacturers have to provide any evidence that their products are effective for the stated purpose. There is also no government-imposed minimum standards regarding quality or concentrations.
That lack of research and study also means that interactions between supplements and other substances are largely unknown, as are the long-term effects of a given dosage, and if certain ethnic or age groups tend to have bad reactions.
This doesn't mean that any of the substances available are not useful or helpful for something WRT human health, but we just don't know, and are not likely to find out anytime soon. Conducting studies is expensive, and you just might find out that the product you are testing doesn't actually do what people think it does.
A lot of the supplement industry IS snake oil selling that can be dangerous at worst and a big waste of money at best.
Don't get me started on homeopathy.
I would first see a doctor to get some bloodwork done to see if you are deficient in any areas, and if it is determined that you are, then eat
foods rich in those nutrients rather than synthetic pills. If you have a poor or limited diet, a daily multivitamin is probably a good idea. I have an excellent diet but my doctor just started me on Flintstones for the extra zinc and iron.