Food and nutrition.pdf

148 Nutrition Disorder Related to Foodsupplements may explain part of this apparent discrepancy, althoughanalysis showed little statistical difference in mean dietary intake for thoseindividuals taking a specific supplement compared with those who didnot take the supplement.The body pool of ascorbic acid reaches a maximum of approximately20 milligrams per kilogram. Women require an intake of 75 mg per dayand men require an intake of 150 mg per day to achieve this ascorbic acidlevel in plasma. This finding was supported by a clinical trial that showedthat a daily intake of 60 mg was insufficient to maintain this plasmaconcentration.Vitamin A deficiency does not seem to be a particular problem inolder persons, Although NHANES I and NHANES II (the National Healthand Nutrition Examination Surveys) reported that half the studypopulation over age 65 had vitamin A intakes at or less than two-thirdsof the RDA, only 0.3 percent of the NHANES older population had lowvitamin A blood levels. Whether vitamin A supplement use can accountfor the observed discrepancy is unknown, but similar data suggest thatolder individuals can maintain normal vitamin blood levels even withreportedly low dietary intakes.Previous studies have revealed a generally lowered vitamin D statusin older people, chronically ill individuals, and those living in institutionswith little or no exposure to sunlight. Because the vitamin D endotrinesystem is the major regulator of intestinal calcium absorption, a reducedvitamin D status might promote a negative calcium balance in olderpeople.Two studies in the United States have found dietary intake of vitaminD to be approximately 50 percent of the RDA for older subjects. However,ultraviolet light induced endogenous production of vitamin D is the mainexternal factor in maintaining adequate vitamin D status. Because sunlightexposure activates vitamin D precursors in the skin, it has beenrecommended that older people obtain at least minimal sunlight exposure(10 to 15 minutes) two or three times a week. Increased sun exposure mayhelp compensate for aging skin's decreased capacity to produce theseprecursors. Supplements may be necessary to compensate for inadequatesunlight exposure due to seasonal variation in northern latitudes.Moderation of sun exposure should be recommended becauseoverexposure to the sun is a strong risk factor for skin cancer.There is no evidence that older individuals are deficient either indietary intake or tissue levels of vitamin E. Despite statements thatmegadose vitamin E supplements retard the aging process and preventatherosclerosis and cancer, its use to treat or prevent other conditions hasnot been established,