Scanning electron micrograph (SEM) of crystals of Vitamin C ( ascorbic acid ) showing the monoclinic crystal structure. Vitamins are compounds required for the normal functioning of metabolism, but which are not synthesised by the body. They must be obtained from the diet. Vitamin C is most easily acquired from fruit and vegetables. The average adult requires 70-100mgs/day. Ingestion of large amounts (1-5gm/day) is sometimes suggested as a prophylactic against colds. There is little evidence to support this. The excess is eliminated in the urine, and since ascorbic acid is partially metabolised to oxalate, heavy consumption of Vitamin C supplements may lead to the formation of urinary stones. A deficiency of Vitamin C in the diet can lead to the diease scurvy, due to a failure in the metabolism of collagen, an important component of connective tissue. Magnification: X 14 at 35mm size.