<prompt> Clinical effect of vitamin D is reduced by ?Simultaneous ingestion of phytatesSimultaneous ingestion of lactoseAcidic environmentNone  <response>: Ans. is a i.e., Simultoneous ingestion of phytates The main clinical effect of vitamin D is to enhance intestinal absorption of calcium. With an average intake of 1000 mg of calcium its net intestinal absorption is only 150-250 mgday. Calcium is absorbed mainly in the duodenum and jejunum proximal intestine by an active transpo mechanism regulated by 1, 25 OH2 D, calcitriol. Parathormone indirectly promotes absorption of calcium by increasing the renal synthesis of 1, 25 OH2 D3. Dietary lactose, proteins and an acidic environment promote calcium absorption. On the other hand, phytates, phosphates, oxalates, tetracycline and and alkaline environment impair calcium absorption. 