Significance of Vitamin A (Retinol) in Ageing

摘要

In recent years, studies involving animal models, case reports, and some epidemiological studies haveindicated that an accumulation of vitamin A in the liver is linked to low bone mineral content, fracture risk, and henceosteoporosis. While vitamin A in its physiological level acts as an inducer of bone matrix protein (osteocalcin) and matrixGLA protein in the osteoblast cells (bone formation), excess reinoic acid (a metabolic product of vitamin A) supressesosteoblastic activity and stimulates osteoclast formation (bone degradation). There also appear to have an antagonisticor synergistic interactions between vitamins A and D, influencing bone metabolosm; such effects are dose related. Theseeffects could be of concern, especially for the older persons, because of the age-associated cumulation of vitamin A in theliver. The vitamin A status in elderly population, however, has not been as well documented as in an earlier age. In effect,the Food and Nutrition Board of National Academy's Institute of Medicine has not made any differenciation in it'srecommendation for the Dietary Reference Intake (DRI) of vitamin A between 14 years and >70 years old individuals.This report will delineate the ageing differences in metabolic availability of vitamin A and that such differences areindependent of its intake. The report will also attempt to formulate a hypothesis that in old age, deficiency of vitamin A isnot a concern but its potential toxicity involving bone.