This is relevant for US readers only. Most countries do not usually fortify juices, milk or yogurt. I don't know about the situation in Singapore (where the stu

This is relevant for US readers only. Most countries do not usually fortify juices, milk or yogurt. I don't know about the situation in Singapore (where the study's participants live), but as UVB and vitamin D production remain constant year-round in Singapore I guess their juices and food are not fortified either.