I take 1000 since I finished Chemo as told by the Nurse in charge of Oncology. Thing is majority of the population actually have low Vitamin D, its not unusual at all. It further plummets through Chemo. Mine was low and 3 months after chemo I had bloods done, it was super high and I take Arimidex, so that definitey doesnt affect it. I do wonder though, even with high Vit D levels, my bone scan revealed 6 months after Chemo that I had Osteoporosis in my neck and lower back! chemo related they said GRRRRRRRRRR. So now have prolia injections twice a year. Melinda xo