When should you take a multivitamin? Pretty much never. They are expensive pee makers. If you are not low on anything, there is no point in taking them. If you are low on X, you should take vitamin X, instead of a bunch of everything. It addresses the problem faster and in a more effective way than multivitamins. You are better off buying 2-3 vitamins directly and taking the appropriate dosage than the low dose of multis...
You're a fucking idiot. 1) Some molecules mask deficiencies in others. Various B-vitamins come to mind. 2) You going to get a quarterly panel to monitor deficiencies? 3) Your stupidity is terminal.
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