Influence of dietary constituents on intestinal absorption of aluminum

Abstract

Orally-ingested aluminum compounds have been implicated in the development of dialysis encephalopathy, osteomalacic dialysis osteodystrophy and other disorders in both hemodialyzed and nonhemodialyzed patients suffering from chronic renal failure [1–10]. Both dialysate aluminum content [7, 11, 12] and aluminum-containing phosphate binding agents [12–15] have been identified as contributing to hyperaluminemia in uremic patients. The health threat from dialysate fluids has been reduced by the recommendation that the dialysate contains less than 10 µg/liter of aluminum [16]. Alternative phosphate-binding agents which do not contain aluminum are available but these agents are not free of problems [17], and uremic patients continue to ingest significant doses of aluminum-containing phosphate binding agents. Aluminum is the most common metal in the biosphere of humans but, aside from uremic patients, causes no widespread toxicity. This may be as a result of the extremely limited solubility of aluminum at the pH range of the small intestine and blood [18]. Advances in analytical chemistry have made it possible to measure picogram quantities of aluminum in body fluids, thus enabling accurate determination of plasma aluminum levels in the part per billion (µg/liter) range. These analytical techniques have shown that orally ingested aluminum-containing antacids elevate plasma aluminum levels in man [13]. Balance studies monitoring aluminum absorption and elimination revealed an average positive balance from 23 to 313mg of aluminum per day when diets were supplemented with 1 to 3g of aluminum per day [15]. These studies show that a small fraction of the ingested aluminum is absorbed. This absorption presents potential toxic effects to uremic patients whose ability to eliminate aluminum is impaired. In addition, Slanina et al [19] have shown that addition of citric acid to aluminum-supplemented dietary regimens results in blood aluminum levels that are significantly higher than those found in subjects treated with aluminum-supplemented dietary regimens alone. This result suggests that dietary factors may contribute to aluminum absorption. This study was undertaken to determine if the form of aluminum present in the intestinal lumen significantly affects the absorption of aluminum following oral ingestion.