Once the body has made enough, it will produce no more. Too much Vitamin D can be toxic and lead to bone loss. Testing of 10 samples of infant formula revealed seven with more that twice the Vitamin D content reported on the label, one of which had more than four times the label amount. Vitamin D is toxic in overdose. This demonstrates adequate mineral absorption occurs from a predominantly vitamin D-free transport mechanism.
Vitamin D is part of the mechanism to break bone down so that it can then stretch and grow.
Thus an overdose of D can eventually lead to osteoporosis. Vegetarian and Vegan Nutrition, by George Eisman, M.A., M.Sc. Do them a huge favor and forward the URL or this entire file to them.