Each person responds differently to UVB exposure and oral intake of vitamin
D depending on such factors as skin
pigmentation, body mass index (vitamin
D is fat soluble), age, condition of digestive tract, other dietary factors, etc.
Dietary vitamin D is insufficient alone to significantly reduce the risk of most cancers since the ingested amounts, up to 200 to 400 I.U. per day, are too low [Grant and Garland, in press]. Evidently, 600 to 1000 I.