IsItBullshit: taking vitamins/supplements has no noticeable positive effect

Can’t remember where, but a while ago I heard something about these things being mostly placebos to make you feel like you’re benefiting yourself. I’ve never taken them before so I’d have no idea. My mum also told me they’re a load of bollocks when I asked her to get me some when I was close to being anaemic. Surely there’s at least some benefit but will there be any noticeable changes in everyday life? Or long term?