Vit D can cause all sort of side effects if too high a dose. Know for a FACT! Been there done that! A doc tried giving me 12,000 units a day for 7 days to try making my parathyroid enlarge, ( they are the size of a grain of rice normally) I flushed them, they did the test, ( I lied and told him I took it all) and no en;argued parathyroid. 600 units can cause stomach probs as well as intense joint pain. Joint pain can occurs at 400 units daily . It also can cause constipation .

Black stools and some slight nausea .