5. Conclusions

This study raises a number of questions about the real effectiveness and potential risks of dietary supplements.

Among the products presenting study results, very few mention bioavailability, i.e. the presence of the ingredient in the bloodstream once it has passed through the digestive mucosa. And it is even rarer to find products that mention studies that include the dosage of the ingested ingredient in skin tissue. Even if vitamins and minerals have a certain bioavailability and can pass into the bloodstream, there is still a great deal of uncertainty as to their delivery to skin tissue. And in the case of more complex molecules, there is a high risk that they will be metabolized before reaching the skin. In fact, studies showing the positive effects of nutritional supplementation mainly concern deficient populations.