Objectives: To measure the availability of oxalate normally extracted when making tea from two commercially available black teas bought from a supermarket in Christchurch, New Zealand in July 2001.
Design, subjects and intervention: A randomized double crossover study. Six students and four staff consumed six cups of each brand of tea both with and without added milk over a 24 h period. A total urine collection was taken for the initial 6 h followed by a further 18 h. The oxalate content of the urine voided was measured using an enzyme kit method and the availability of the soluble oxalate consumed was measured for the 6 h and the total 24 h sample.
Setting: University campus.
Results: The mean soluble oxalate content of black tea in the two different commercial tea bags was respectively 6.1 and 6.3 mg soluble oxalate/g tea. The mean availability of the oxalate extracted from tea measured over a 6 h period ranged from 1.9 to 4.7% when tea was consumed without milk. The availability of the soluble oxalate from tea ranged from −3.0 to 2.3% for each of the two brands of tea investigated over a 24 h period.
Conclusion: These studies show that consuming black tea on a daily basis will lead to a moderate intake of soluble oxalate each day, however the consumption of tea with milk on a regular basis will result in the absorption of very little oxalate from tea.
Sponsorship: Lincoln University.
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The authors wish to acknowledge Trevor Walmsley, Canterbury Health Laboratories, Christchurch, NZ, for his assistance with the analysis of urinary oxalate and Professor D McNeil, Plant Sciences, Lincoln University for his assistance with the statistical analysis of the data.
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Savage, G., Charrier, M. & Vanhanen, L. Bioavailability of soluble oxalate from tea and the effect of consuming milk with the tea. Eur J Clin Nutr 57, 415–419 (2003). https://doi.org/10.1038/sj.ejcn.1601572
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