Are you sure you're not confusing D3 with Vit. A toxicity, which definitely can be fatal in overdose? I think lately there's been a realization that D is not really as toxic as we have been led to believe for many years (D3, at least), with some people saying that our estimates of daily requirements are absurdly low, the result being that most of us are actually chronically underdosed, and they are now saying the more the better. Not to mention the anti-cancer effects. I think even 5,000IU is probably a safe dose of D3 for most people, 10,000IU in deficiency states, although each person has to decide for themselves, of course.