Interactions between drugs and vitamins at advanced age.

Drug consumption increases at advanced age due to increased morbidity. At the same time the state of repletion is reduced for several vitamins. Physiological and kinetic alterations in the elderly are reviewed in order to analyse possible interrelations between these two phenomena. At high age the status of all vitamins is compromised by reduced food intake. Decreased active intestinal transport and an increased propensity for atrophic gastritis may reduce the absorption of vitamins A, B1, folate and B12. Decreased exposure to sunlight and reduced cutaneous synthesis impair the vitamin D status. Studies on the state of vitamin repletion in hospital patients indicate a specific response of vitamins A, B1, B6 and C to drug administration at advanced age. Reduced food intake in the elderly is further compromised by drugs that impair appetite and absorption. Anticonvulsives and other drugs that induce hepatic microsomal enzymes accelerate vitamin D metabolism and aggravate post-menopausal osteoporosis. Acid inhibiting agents increase achlorhydria and reduce vitamin B12 absorption. Renal clearance of acidic drugs such as acetylsalicylic acid and barbituric acid, which is impaired at high age, is further reduced by high doses of vitamin C. Vitamin B6 reduces the therapeutic effect of L-dopa. When recognised, the negative effects of drug-vitamin interactions can be compensated by adequate vitamin supplementation and by adaptation of drug dosing.