Mayo Clinic just provided another reason to love cranberries … and likely, all other berries and food sources of polyphenol-type antioxidants.
We've reported on some of the many studies that find substantial animal or human health benefits from foods rich in polyphenol-class “antioxidant” compounds.
Two flavonoid-type polyphenols in particular – proanthocyanidins and catechins – appear highly beneficial to brain, heart, immune-system, and overall health.
Aside from berries, the richest food sources of flavanols are cocoa, grapes, and tea … with raw (non-Dutched/alkalized) cocoa and dark chocolate topping the list.
To learn how flavanols and other polyphenols work their health-enhancing magic, see our sidebar, “Berries and brethren influence genes beneficially”.
Berries and brethren influence genes beneficially
There's ample evidence that diets rich in berries or other foods rich in polyphenols help deter the oxidative cell damage and inflammation caused by free radicals.
However, it's becoming clear that polyphenols generally do not exert direct antioxidant effects in the body… at least not to a very substantial extent.
Instead, polyphenols bring their benefits by indirect, so-called “nutrigenomic” effects on gene switches in our cells.
Polyphenols' nutrigenomic effects tend to yield anti-inflammatory responses and beneficially modulate the body's own “antioxidant network”… which includes enzymes, lipoic acid, CoQ10, melatonin, and vitamins C and E.
These indirect effects probably bring most of the health benefits associated with polyphenols and other “antioxidants” from fruits, vegetables, tea, cocoa, whole grains, and nuts.
According to USDA data, the average American's diet provides about 852mg of polyphenols daily.
Polyphenols abound in certain plant foods – especially raw cocoa, berries, tea, coffee, extra virgin olive oil, beans, and whole grains – and are commonly called “antioxidants”.
However, only small amounts of these compounds get into our blood, and they don't exert strong “direct” antioxidant effects in the body … but they appear to exert strong indirect effects on oxidation and inflammation.
Polyphenols benefit health by exerting generally desirable “nutrigenomic” influences on the expression of various genes.
Procyanidins abound in dark-hued berries and in açaí, grapes, red wine, cocoa, and tea, while anthocyanins abound in cherries, açaí, and most berries.
Meanwhile, extra virgin olive oil is rich in hydroxytyrosol … the second most potent polyphenol in terms of antioxidant and nutrigenomic activity in the test tube … with strong, clinically documented vascular benefits.
Cranberries' credible record of health benefit
France affirmed the credibility of the best known belief about cranberries when, in 2004, it approved the first health claim for cranberries.
The French authorities concluded that daily cranberry (whole or juice) intake providing at least 36mg of proanthocyanidins deters the adhesion of E. coli bacteria to urinary tract walls, and may fight urinary infections.
It's less well known that many prior animal and human studies have detected artery-health and other cardiovascular benefits from berries (Kalea AZ et al. 2009; Chaves AA et al. 2009; Del Bo' C et al. 2010; Kristo AS et al. 2010; Schini-Kerth VB et al. 2010; Kawai Y 2011).
Now, cranberries' health rep gets a boost from research out of the Mayo Clinic and College of Medicine in Rochester, Minnesota.
Mayo Clinic trial finds cranberry juice reduces a key artery risk factor
The Mayo team conducted a small, controlled clinical trial, and found that two glasses of cranberry juice a day reduced a known risk factor for hardening of the arteries.
Unlike many other berry-artery studies, they saw no effect on the function of the endothelial lining the arteries,
However, the group given cranberry juice enjoyed a drop in the number of endothelial cells that produce a compound called osteocalcin, which has been linked to hardening of the arteries.
As the team led by Amir Lerman, M.D., wrote, “Although endothelial function remains unaffected, our study demonstrates for the first time a potentially beneficial differential effect of cranberry juice on osteoblastic EPCs [endothelial progenitor cells], which are linked to the development of atherosclerotic lesions.” (Flammer AJ et al. 2012)
“This preliminary finding is of particular interest as it might partly explain the proposed beneficial effect of cranberry juice and other polyphenol-rich nutrition on cardiovascular health.” (Flammer AJ et al. 2012)
The study was funded by cranberry giant Ocean Spray and the U.S. National Institutes of Health (NIH).
Trial puts cranberries to the artery test
Dr. Lerman's team recruited 84 volunteers – whose average age was 49.5 – for a double-blind, randomized, controlled trial.
Out of the total enrolled, 69 participants completed the trial and provided usable data.
The volunteers were randomly assigned to drink either two glasses of a placebo beverage or double-strength Ocean Spray Light cranberry juice, for four months.
The researchers examined the participants' arteries using a method called peripheral arterial tonometry (EndoPAT).
In addition, the volunteers gave blood samples to allow the scientists to look for markers indicating the participants' blood levels of endothelial progenitor cells (EPC) and osteocalcin.
In what appears to be a new finding about the beneficial effects of polyphenols on artery health, the cranberry-juice group enjoyed reductions in the expression of genes that promote osteocalcin production by EPCs.
Surprisingly, given the outcomes of animal and human studies using other berries, there were no differences between the groups' endothelial functions.
As the researchers noted, their findings may hold broader implications: “… [the positive outcome of] this dietary intervention could therefore influence the dynamic process of atherosclerosis and might expand knowledge about the healthy effects of polyphenol-rich fruits and vegetables in general.” (Flammer AJ et al. 2012)
We agree, and believe it's wrong to focus on any one polyphenol-rich plant food.
Thanks to their distinct polyphenol profiles, whole plant foods – especially raw cocoa, berries, onions, extra virgin olive oil, tea, whole grains, nuts, herbs, and spices – exert diverse, overlapping and likely synergistic beneficial health effects.
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