It depends on your status. If you’re deficient, 400IU won’t really help. Getting a serum (25OHD) test is the easiest way to find out, but otherwise following the advice in the vitamin thread is likely to help correct poor status. You don’t need to go crazy with vitamin A, but make sure you get the RDA. A cod liver oil capsule plus 3-5000IU (after an initial higher dose) of vitamin D3 would be a good combo.