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Gastro-intestinal availability of aluminium from tea
J J Powell1, S M Greenfield, H G Parkes
1Gastrointestinal Laboratory, Rayne Institute, St Thomas' Hospital, London, UK.
Summary
Aluminum speciation in black tea was studied. Most aluminum remained bound at low pH but became more available at higher pH, suggesting limited absorption in the small intestine.
Area of Science:
- Food Chemistry
- Analytical Chemistry
- Toxicology
Background:
- Aluminum (Al) is present in black tea.
- Understanding Al speciation is crucial for assessing its bioavailability and potential health effects.
Purpose of the Study:
- To investigate the in vitro speciation of aluminum in black tea infusion.
- To determine the effect of simulated gastric conditions and subsequent pH changes on Al speciation.
- To assess the potential for Al absorption from tea in the human gastrointestinal tract.
Main Methods:
- Ultrafiltration using 3000, 10,000, and 30,000 Da cut-off filters to assess Al speciation.
- Simulated gastric conditions (pH 2.3) and intestinal conditions (pH 6.5) were applied.
- High-resolution 1H nuclear magnetic resonance (NMR) spectroscopy was used to analyze polyphenol breakdown in ileostomy effluent.
Main Results:
- In black tea infusion (pH 4.8), 78% of Al passed through a 3000-Da filter.
- Addition of simulated gastric juice (pH 2.3) increased Al passage through the 3000-Da filter to over 90%.
- Adjusting the pH to 6.5 significantly reduced Al passage to approximately 5%.
- No low molecular weight breakdown products of tea polyphenols were detected in ileostomy effluent.
Conclusions:
- A small proportion of aluminum in black tea is potentially absorbable in the small intestine.
- Estimating systemic aluminum absorption solely from total urinary excretion may be misleading.
- The speciation of aluminum in tea is highly dependent on pH conditions within the gastrointestinal tract.