Someone help. I have no justification to stop people I care about from buying supplements. I've heard they are useless, but I can't find sufficient evidence to prove either side. A routine Internet search just brings up a wall of pseudo-news "Are Vitamins Really Useful?" articles and no links to primary sources. The best I could do is

>https://annals.org/aim/fullarticle/716521/routine-vitamin-supplementation-prevent-cancer-cardiovascular-disease-recommendations-rationale

and I couldn't find anything on fatty acid or probiotics.