Gastrointestinal absorption of aluminium and citrate in man

Aluminium (Al) is an abundant terrestrial element, but toxic to tissues, including brain. The body is largely protected because systemic Al absorption is very low and in normal individuals almost all absorbed Al is excreted from the body. However gastrointestinal (Gl) absorption is enhanced by organic acids, including citrate. Aluminium and citrate Gl absorption was measured in three healthy males, aged 40-46. After overnight fast, subjects drank a 100 ml fruit drink containing 280 mg Al and 3.2 g citrate (104 and 167 mM, respectively). Al was measured in timed blood and urine samples by GFAAS and serum citrate by enzymatic assay. Blood Al peaked by an increase of 13 +/- 2.1 micrograms/l after 87 +/- 19 min then fell slowly over 24 h. Plasma citrate peaked after 32 min, returning to baseline by 90 min. Al was excreted at a constant rate for the first 24 h, 0.4% of the dose being excreted in urine by this time. It is unlikely that Al is absorbed as Al citrate because the blood citrate peak preceded the Al peak by 45-60 min.