Q. Just wanted to briefly share my recent experience in order to encourage people to be more cautious. I have a history of irritable bowel syndrome and chronic fatigue syndrome. I started supplementing Vitamin D3 orally at 1000 IU per day and gradually increased to 5000 IU per day over a period of a year or so. I was and am, under the care of a qualified nutritionist, we tested my 25 OHD levels and serum calcium every 3 months. My serum 25OHD level hit the 'therapeutic zone' when I increased to 5000 IU, which most patients apparently comfortably tolerate. However, it unequivocally caused bowel inflammation in me and severe constipation - and it took weeks for the flare up to subside after stopping the supplementation. During the whole period I only experienced adverse effects from my 'experiment'. Sensitive individuals please take note.A. Thanks for sharing, readers of my newsletter know that I am cautious about high dose use of this vitamin while there are many doctors who are prescribing massive amounts.