Interactions between zinc and vitamin A: an update

• Published in: The American journal of clinical nutrition 1998-08, Vol.68 (2S), p.435S-441S
• Main Authors: Christian, P, West, K.P. Jr
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; dietary mineral supplements; Health and Pathology; Humans; intestinal absorption; literature reviews; Liver; Medical sciences; Metabolic diseases; Metabolism; nutrient deficiencies; nutrient transport; nutrient-nutrient interactions; nutrition physiology; nutritional status; Other nutritional diseases (malnutrition, nutritional and vitamin deficiencies...); pregnancy; Proteins; Public Health; synergism; trace element deficiencies; vision; Vitamin A; Vitamin A - metabolism; Vitamin A Deficiency - complications; Zinc; Zinc - deficiency; Zinc - metabolism
• ISSN: 0002-9165; 1938-3207
• DOI: 10.1093/ajcn/68.2.435s

Zinc status influences several aspects of vitamin A metabolism, including its absorption, transport, and utilization. Two common mechanisms postulated to explain this dependence relate to 1) the regulatory role of zinc in vitamin A transport mediated through protein synthesis, and 2) the oxidative conversion of retinol to retinal that requires the action of a zinc-dependent retinol dehydrogenase enzyme. However, evidence of an effect of zinc intake on vitamin A status from animal experiments is inconclusive, mainly because of the use of inadequate control groups. The higher weight of control animals as compared with the zinc-deficient ones in these experiments, even though pair fed, makes it difficult to isolate effects of zinc deficiency per se from those of generalized protein-energy malnutrition. A curvilinear relation has been suggested to describe an effect of plasma zinc on vitamin A transport. In humans, cross-sectional studies have more often than not shown a weak linkage between vitamin A and zinc status. Randomized trials have failed to show a consistent effect of zinc supplementation on vitamin A status. In disease states in which liver function is severely compromised and both zinc and vitamin A metabolism and transport are impaired, serum zinc and vitamin A concentrations tend to be positively correlated. In conclusion, clear evidence of synergy between these 2 micronutrients and its public health significance in humans is lacking. Research should focus on understanding this interaction in the context of coexisting moderate-to-severe zinc and vitamin A deficiencies in the population.