...But maybe you should watch the tea.
Many studies have shown that drinking tea can inhibit absorption of important dietary minerals such as iron. Now researchers at the University of Wisconsin in Madison have begun identifying chemical clues to what might be happening, as well as possible ways to temper tea's adverse effects on nutrition.
They focused on the solubility of iron and calcium in brews of black, green, oolong and instant (black) teas. The reason, explains Lauren Jackson, one of the researchers, is because "in general any mineral is going to be more bioavailable if it's soluble." The data she and colleague Ken Lee report in the January/February Journal of Food Science show that iron was totally soluble in instant tea, but only 85 percent soluble in green and oolong, and just 69 percent soluble in regular black tea. Tea's effects on calcium were even more pronounced. Calcium was most soluble--88 percent--in oolong, 66 percent soluble in black, 46 percent soluble in green and only 35 percent soluble in instant teas.
In an effort to identify what might be happening, the pair added either the enzyme tannase or lemon juice to each of the brews. Tannase, which had an effect on only black tea, increased iron solubility 17 percent and calcium solubility 11 percent. This suggests, Jackson says, that one reason for the minerals' initial insolubility was their binding to some of the large polyphenolic molecules that tannase eventually broke down. Lemon juice increased calcium's solubility even more in two of the teas--24 percent in black and 15 percent in green tea. It also increased iron's solubility 7 percent in black tea. The researchers speculate that one or more of the juice's organic acids are responsible.
Jackson and Lee believe their findings suggest the prospect of reducing some teas' detrimental effects on mineral bioavailability, perhaps with something like a tannase pretreatment. And for the calcium-conscious tea drinker, a wedge of lemon perhaps?
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|Title Annotation:||research on countering tea's adverse effects on absorption of dietary minerals|
|Date:||Mar 12, 1988|
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