Bilberry extract 200 mg/(kg ■ day) administered intraperitoneally to euthy-roid rats increased radiolabeled triiodothyronine (T3) transport into the brain, compared to vehicle only (21). Postulated mechanisms include central or peripheral inhibition of L-thyroxine's (T4) deiodination to T3; inhibition of T3 protein binding; or enhanced T3 binding to carrier proteins in the brain capillary wall (21). Whether bilberry could interact with thyroid replacement therapy remains to be seen.

Studying a diabetic rat model, Cignarella and colleagues (1) found that administration of an extract from the leaves of blueberry plants caused a 26% reduction in plasma glucose. This was also accompanied by a 39% decrease in plasma triglycerides. Whether this reduction in glucose levels might result in a clinically significant interaction in patients taking antidiabetic agents is unknown, because the glucose lower effects have not been studied in humans. Likewise, whether the triglyceride-lowering effects of hypolipidemic agents used in humans would be enhanced by coadministration of anthocyanidins is unknown.

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