Since the turn of the century, raw milk has been pasteurized to destroy microorganisms that may enter milk accidentally from environmental and human sources. Nearly all milk marketed in the U.S. is pasteurized. Pasteurization has either no or practically no effect on milk's major nutrients such as protein, calcium and, riboflavin. A minimal reduction in some vitamins such as thiamin (B12), and C in pasteurized milk has been reported. It is still a good source of these vitamins. Some people feel that raw milk's nutrients are destroyed by pasteurization, but there is no scientific evidence that raw milk is more nutritious than pasteurized milk. The U.S. Department of Agriculture applies the same nutrient value to raw and pasteurized milk.