Food and nutrition.pdf

Nutrients 61weakness, low blood sugar, increased bleeding tendency, anddegenerative changes.The comments that vitamin doses in excess of the RDA may produce"optimal" health are pure speculation, unsupported by any facts in humanmetabolism, and contradicted by the toxicity of vitamin and mineral dosesin excess of the RDA. "More is better" is a slogan, not science. More issometimes better, sometimes worse, but always costlier.Vitamin A (Retinol, Carotene)Vitamin A is fat soluble, it is an antioxidant and occurs in two forms- retinol and carotene. The RDA [Food and Nutrition Board, NationalAcademy of Sciences - National Research Council- Recommended DietatyAllowances. ] for adults is 1000 micrograms RE (Retinol Equivalents. 1RE = 1 microgram retinol or 6 micrograms carotene).The allowances, expressed as average daily intakes over time, areintended to provide for individual variations among most normal personsas they live in the United States under usual environment stresses. TheRDA's given are the higher of adult males or females, for more precisedata refer to the RDA tables.Because vitamin A and carotene exist in more than one chemical form,and because they are not equally active, it is usual to give the name retinolto the pure vitamin A. Thus the total vitamin A activity of a food, its retinolequivalent, is determined by how much it contains of retinol, chemicalsvery similar to retinol but not as active, and a range of carotenes also ofvarying activity.Vitamin A maintains the skin and mucous membranes. Promotesgrowth, strong bones, healthy skin, hair, teeth and gums. Builds upresistance to respiratory infections and shortens the duration of diseases.It counteracts night blindness and aids in the treatment of many eyedisorders. Night blindness is an early symptom of a deficiency of vitaminA:In a dozen case-control and cohort studies, intakes of fruits andvegetables containing carotenoids has been associated with a reduced riskof lung cancer. In contrast little relationship has been found between intakeof preformed vitamin A (retinol) and this disease.Available data thus strongly support the hypothesis that dietarycarotenoids reduce the risk of lung cancer, but the data also are compatiblewith the possibility that some other factor in these foods is responsiblefor the lower risk. The recommendation to eat a'varipty of fruits andvegetables is reasonable, but leaves much to chance; if carotene is theanticancer agent, intake of specific fruits and vegetables should be advised.[Willett, W.C, Vitamin A and lung cancer, Nutrition Reviews, 48:201,