Before starting on recommended supplements such as zinc, magnesium, selenium, etc. would it be unwise to take up to the RDA of each mineral if testing is unavailable / denied / too expensive? I figure that since it's very difficult to overdose from dietary sources for most things you'd have to be going it some to take the RDA in pill / capsule form and get over and above from your diet.
For instance, I'm thinking of taking 10ug zinc, 200mg magnesium citrate and 50ug selenium. I think it's pretty conservative in terms of the quantities but testing is too expensive to see where my levels are prior to supplementation.
Is my thinking completely flawed?