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Cranberry anthocyanins show low levels of bioavailability, study

By Jane Byrne , 19-May-2010

A new US study shows cranberry juice anthocyanins have only limited absorption but the researchers note that, in spite of this low bioavailability, the levels may be sufficient to generate a sustained health beneficial effect in terms of cell metabolism and gene expression.

Cranberries contain a variety of anthocyanins, which are a sub-group of flavonoids, with reports in the literature suggesting flavonoids are powerful antioxidants, protecting the body from oxidative stress.

Health benefits recently linked to cranberries include cardioprotective effects, anti-cancer properties and reversal of age-related motor behavioural deficits.

However, the authors of the study, which was published in The Journal of Nutrition, said that teh compounds responsible for this bioactivity have not yet been fully determined.

The researchers, based at Tufts University and Boston University Medical Center, said that, to their knowledge, there have been no detailed pharmacokinetic studies of anthocyanins after acute cranberry juice consumption. They added that little is known about the absorption and metabolism of anthocyanins.

And the trigger for their research, they said, was a desire to increase understanding of the bioavailability and benefits of these compounds

Method

Fifteen volunteers with an average age of 62 and with established coronary artery disease were recruited to participate in this research, said the authors.

They explained that after fasting overnight, the participants arrived at the Boston University Medical Center where they each drank 480 ml of a double-strength cranberry juice containing 94 mg anthocyanins.

Plasma samples, continued the scientists, were taken immediately prior to juice consumption and then at intervals of one, two, three and fours hours subsequent to drinking the juice.

They added that urine was collected at the beginning and end of the four hour study, with samples then analyzed for anthocyanin concentrations.

Findings

Following cranberry juice consumption, the researchers said they were able to detect 7 of the 15 known cranberry-derived anthocyanins in both blood and urine, while highest plasma concentrations tended to occur within 1.4 hours after consumption.

However, they found that the concentrations detected in plasma confirmed a relatively low level of intestinal absorption of these compounds. In addition, the scientists said they found significant variability among individuals in terms of when and how much of the anthocyanins were absorbed and excreted.

Recovery of these compounds in the urine ranged from 0.078-3.2 per cent, added the authors.

This variability, they explained, might be due to small genetic differences (polymorphisms) leading to differences in absorption and metabolic clearance between individuals or to differences intestinal microorganism populations that break down and metabolize the various anthocyanins.

The authors concluded that circulating anthocyanin levels after cranberry juice consumption are too low to have health beneficial effects in terms of free radical quenching.

But they concluded that the levels of the compounds may be sufficient to influence cell signal transduction, gene expression, and cellular metabolism and could have a more sustained health beneficial effect.

Source: The Journal of Nutrition
Published online ahead of print: doi:10.3945/jn.109.117168
Title: Anthocyanins are Bioavailable in Humans following an Acute Dose of Cranberry Juice
Authors: P. E. Milbury, J. A. Vita, J. B. Blumberg

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