There are two problems with supplement formulations. First of all sometimes supplements contain adulterants which seems to be a particular problem with herbs and weight loss supplements. I am not going to talk about adulterates in supplements further.
Another difficulty is that supplements very frequently are formulated for high absorption and/or quick absorption. Formulators of supplements assiduously peruse PubMed and then formulate supplements, highly successfully, for high absorption and/or quick absorption. Manufacturing quality is excellent. Individuals manufacturing these supplements are honest and not cutting corners in manufacturing.
The supplements do exactly what is advertised, however, what is advertised, as is often the case, is not what individuals need or is best for individuals. The only difficulty is these supplements, which are manufactured to stringent specifications, can have adverse effects on health.
The simple fact of the matter is than supplements must first be bioavailable in the gut. Yes, supplements must be bioavailable systematically but only after being bioavailable in the gut. This one small detail about supplements changes everything about supplements.