Bioavailability of soluble oxalate from tea and the effect of consuming milk with the tea

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.

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.

University campus.

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.

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.