The subject of what is and what isn’t a necessary ingredient for life has been up to debate for several decades; really, more or less since the discovery of vitamin C.
any of a group of organic compounds that are essential for normal growth and nutrition and are required in small quantities in the diet because they cannot be synthesized by the body. (from Wikipedia)
The number of vitamins recognized internationally has changed somewhat, as compounds are determined to be “essential” or “nonessential”, and what is considered an essential vitamin for one species is not the same as for another. For example, if a cat is given a diet which is lacking in taurine it will develop developmental or muskuloskeletal issues; if a human is deprived of taurine in their diet, they have the capacity to manufacture it from other food sources.
Any food component used for medicinal purposes. Examples include minerals, vitamins, amino acids, and hormones. Rules for the sale and promotion of these agents have been set forth in the Dietary Supplement Health and Education Act of 1994. Medical Dictionary, © 2009 Farlex and Partners
Essentially nutraceuticals can range from a vitamin complex to powdered reindeer antler or emu oil, depending on the situation. It largely depends on sourcing, but mainly on the intention behind the use of the product or compound.