Vitamin B-12 deficiency anemia can also occur if your small intestine can't absorb vitamin B-12.

CNN: Vitamin deficiency anemia

Recent research has suggested that vitamin C, vitamin B-6 and vitamin B-12 don't deliver all of their purported health benefits.

WSJ: Vitamin D and Calcium Supplements May Not Stop Fractures

Bush says the problem was that patients weren't getting enough of a B vitamin, and that no such safety issues have showed up in the current trial.

FORBES: Magazine Article