The FDA is not the last word in medical knowledge. Science has a place, but our knowledge of the complexities of the human body remain embryonic. I will give you “alternative” medicine is rife with antidotal nonsense, but there are many modalities that don’t fit into the classical “western” medical paradigm. This does not make them valid, just outside the “prevailing view.” Being outside the prevailing view also does not make them in-valid. The things we consider true and valid today may, in a hundred years, be laughed at. Such is the nature of scientific change.There are billions in sales and 100’s of millions in profits every year attributed to vitamin companies. They chose (very wisely) to not have their products tested by the FDA.
As someone with a reasonable amount of training wrt the scientific method, I always ask “what else might explain that?” It keeps me open-minded and skeptical. I am also highly skeptical of “facts“ that are result of consensus vs. experimentation.