While Cod Liver Oil may be terrific and all, and vitamins are a Good Thing, this statement is suspect, IMO. If you inherit a small mouth from your mother and large teeth from your father, no amount of vitamin D is going to make your teeth turn out straight.
Ironically, it was a dentist who accumulated data to the contrary. Nutrition during periods of physical develop does indeed influence genetic expression. You may have seen several references/links to Dr. Weston A. Price on this thread, his work makes for a very interesting read.
May I refer to you: http://www.amazon.com/gp/product/0879838167/qid=1137865582/sr=2-1/ref=pd_bbs_b_2_1/102-8839426-4354504?s=books&v=glance&n=283155
Nutrition and Physical Degeneration