GASTROINTESTINAL AVAILABILITY OF ALUMINUM FROM TEA

The in vitro speciation of aluminium (Al) in black tea infusion (pH 4. 8) was assessed using 3000. 10,000 and 30,000 Da cut-off ultrafilters, and the effect of adding human gastric juice (pH 2.3) and then raisin g the pH to 6.5 were also studied. 78% Al in the tea infusion passed t hrough the 3000-Da ultrafilter, this percentage increased to more than 90% with the addition of gastric juice at pH 2.3, but then reduced to approximately 5% when the incubate was adjusted to pH 6.5. The breakd own of tea-derived polyphenols to low molecular weight phenols in vivo was measured using high-resolution H-1 nuclear magnetic resonance spe ctroscopic analysis of ileostomy effluent, but there was no evidence o f low molecular weight breakdown products from the polyphenols of inge sted tea in this effluent. These results suggest that only a small pro portion of Al in tea is potentially available for absorption throughou t the small bowel. It may be misleading to estimate systemic Al absorp tion from tea drinking simply from total urinary aluminium excretion a s has been done previously.