... 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 ... beta-carotene and other 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 ... food bars containing L-arginine and antioxidant vitamins (Vitamin A, C, and E are all antioxidants). The second group was given bars containing just the vitamin supplements and the third group...