Need some schooling on vitamins and supplements please?

I take a glucosamine/chondroitin supplement for my joint aches. It takes 3-5 days before I notice any difference, but I am convinced it helps. My doctor told me that it is one of the very few supplements that actually does what it says. I also take a good brand of vitamin for eye care based on my eye doctors advise, as I am showing the precursors of macular degeneration.
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