... carotenoids (Vitamin A, 2007), vitamin D is synthesized in the skin when in direct contact with UVB radiation (Vitamin D, 2007), and vitamin K is made by bacteria living in the intestines when insufficient ... clothing, moving to temperate climates, and the tradition of keeping infants indoors), increased skin pigmentation, reduced in- utero exposure, and reduced capacity to synthesize vitamin D with increasing ... vitamin A that they were ingesting (Vitamin A, 2007). Not all vitamins need to be ingested in their final form because the body can synthesize some vitamins from other molecules. Vitamin A...