[Salliter]

yea bottom line too much is poisonous, and its very easy to overdose if taking OTC supplements.

You're half right in that too much is bad for you but it is NOT easy to OD on vit D. According to the link pgsmith posted:
Like most medication, cholecalciferol is certainly toxic in excess, and, like Coumadin, is used as a rodent poison for this purpose. Animal data indicates signs of toxicity can occur with ingestion of 0.5 mg/kg (20,000 IU/kg ), while the oral LD50 (the dose it takes to kill half the animals) for cholecalciferol in dogs is about 88 mg/kg, or 3,520,000 IU/kg. An Overview of Cholecalciferol Toxicosis. The American Board of Veterinary Toxicology (ABVT). This would be equivalent to a 110-pound adult taking 176,000,000 IU or 440,000 of the 400 unit cholecalciferol capsules. I suspect the main reasons for the toxicity fears with certain vitamins is primarily because they (vitamins A, D, E and K) are fat soluble so they get stored in the body's fat cells and used as needed rather than flushed out like the B and C vitamins are. This means it's easier to build up unnecessarily high levels of those vitamins in the body. However, I don't see any reasonably sane individual consuming 400,000 vitamin pills in a short time period.