Vitamin A uptake from foods

PURPOSE OF REVIEW: To review our current understanding of vitamin A uptake from foods. RECENT FINDINGS: There are advancements in understanding the molecular processes involved in vitamin A uptake and the regulation of these processes. A number of genes involved in vitamin A transport and metabolism have been recently identified. The identification of mutations in human genes and targeted disruption of mouse genes have provided further insight as to how these genes contribute to meeting nutritional needs. SUMMARY: The rate limiting steps in the lymphatic absorption of vitamin A involve intracellular processing of vitamin A within the enterocyte. The key steps appear to be related to chylomicron formation and secretion and are closely coupled with fat absorption. The genes encoding serum retinol binding protein, cellular retinol binding protein I and cellular retinol binding protein II have been disrupted by homologous recombination in mice. Studies of these knockout mice indicate that extrahepatic uptake of postprandial vitamin A may play a particularly important role in the maternal-offspring transfer of vitamin A. Further studies of the transfer of maternal dietary vitamin A have important implications for assessing the upper limits of maternal vitamin A supplementation.     

Vitamin A Reserves of Canadians

—A survey of vitamin A and carotene stores of Canadians at five major centres across Canada was completed. Vitamin A and carotene analyses were performed on approximately 100 human liver specimens obtained at necropsy from each location.Age influenced liver vitamin A stores. Children between 1 and 10 years of age had the highest vitamin A stores while a trend toward lower liver stores occurred between 20 and 40 years of age. Females had higher liver carotene stores than males but there was no such difference in vitamin A stores.Subjects from all locations were classified according to cause of death: accidental, heart and coronary artery diseases, cancer, respiratory diseases and a miscellaneous disease group. The mean liver vitamin A and carotene stores of the accidental death group differed only from the cancer group. In contrast to the disease groups, no case with undetectable vitamin A was found in the accidental death group.The mean vitamin A and carotene stores of Vancouver subjects were generally higher than those for the other locations. Montreal showed more values in the 0-40 μg. per g. range than the other locations. Vancouver had the least number (15%), with Halifax, Ottawa and Winnipeg being intermediate (32%). These data suggest the need for improved nutrition, prophylactic treatment in disease states and the need for further research on the utilization and metabolism of vitamin A.