How much you need will be dependent on numerous factors (what a 110lb sedentary female needs and what a 220lb male athlete needs are going to be quite different) and isn’t 100% clear (as Lyle has already mentioned in this thread–lots of debate on the subject). In general, if you aren’t having issues, then you probably are not deficient. That is quite dumbed down, but a lot of people will over do it or find things wrong with them that aren’t wrong at all. Look at your diet and see where things are going and if you might be deficient in something. Overall, if you are getting a variety of animal meats, fruits, and vegetables and perhaps take a multi-vitamin, chances that you are deficient in anything is low. If you are in an area with low sunlight, supplementing with vitamin D (or going to a tanning bed or one of numerous other options) is likely a good idea as well, but those things become high individualized. The main point I’m trying to make is to not go overboard with the supplementation for the sake of it if there isn’t anything wrong in the first place.