by Craig Weatherby
Back in 2004, we reported the encouraging results of a study showing that wild blueberries kept rats’ arteries relaxed after administration of a stress hormone.
For that report, see “Fish Oils and Blueberries Cut Cardio Risks.”
Several kinds of polyphenol-type compounds are known to relax arteries in animals and people, and protect or enhance artery-lining functions in ways that support optimal cardiovascular health.
They’ve become known as “antioxidants”, because many of the polyphenols found in plant foods squelch the pro-oxidant compounds called free radicals… in test tubes.
There’s ample evidence that eating foods rich in polyphenols 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 any significant extent.
Instead, polyphenols bring their benefits mostly by indirect means, via so-called “nutrigenomic” effects on gene switches in our cells (Nicholson SK et al. 2008).
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.
Polyphenols in berries and other plant fefoods: Artery allies?
Several polyphenol-rich foods and beverages tested either in people or in human cells appear to exert very positive effects on artery function (Plotnick GD et al. 2003; Suzuki A et al. 2006; Sánchez M et al. 2008; Chaves AA et al. 2009).
The polyphenols likely to aid arteries most include chlorogenic and caffeic acids (coffee, carrots, apples, strawberries, and pineapple), flavanols (berries, grapes, cocoa, and tea), quercetin (onions), resveratrol (grapes), and tyrosols (olives and extra virgin olive oil).
But many more foods and isolated polyphenols remain to be tested. To varying extents, all fruits, vegetables, nuts, seeds, whole grains, and beans should be beneficial to arteries, because they all abound in polyphenols.
Prior research on the artery effects of wild blueberries suggests that their polyphenols help arteries relax and produce various beneficial effects in artery linings.
Recently, some of those same researchers sought to confirm their prior findings… and pinpoint the reasons why blueberries appear to promote artery health.
Like nitrate-rich veggies, berries eased animals’ arteries via nitric oxide
Researchers from the University of Maine, Northwestern University, and the University of Louisville tested a blueberry-rich diet in rats (Kristo AS et al. 2010).
Wild blueberries were used, and they usually provide higher levels of polyphenol-type antioxidants, compared with cultivated ones.
This difference occurs because polyphenols are produced by plants in response to the pests, fungi, and microbes, which do not as seriously stress berries sprayed with protective pesticides.
They divided the rats into several groups and tested various diet and drug regimens, for eight weeks.
Some animals were given a control diet of standard rat chow, while others were assigned a special chow consisting of eight percent freeze-dried, powdered wild blueberries.
The researchers wanted to see whether blueberries would relax the animals’ arteries, and gave some of the rats drugs that would help pinpoint precisely how the berries worked to produce an easing effect, if any.
They presumed, based on prior research, that the berries would primarily affect the body’s production of nitric oxide (NO), which relaxes arteries.
(The male performance drug Viagra™ works by raising production of NO, thereby boosting blood flow in the relevant body region.)
After eight weeks on the blueberry-rich diet, the rats were exposed to the vasoconstrictor compound called l-phenylephrine, which causes arteries to narrow.
As hoped, the results showed that the narrowing caused by l-phenylephrine was eased significantly in the wild blueberry group.
And because the researchers had also given some of the rats compounds that affect production of NO, they were able to determine that the berries worked in part by boosting production of NO.
As the Maine-based team wrote, “These findings document the potential of wild blueberries to modify major pathways of vasomotor control and improve the vascular tone…” (Kristo AS et al. 2010).
We should note that a prior study by the same team showed that wild blueberries also affected the inflammation pathways controlled by the COX-2 enzyme (Kalea AZ et al. 2010).
This is the same pathway affected by the anti-inflammatory drugs Vioxx and Celebrex, which unfortunately produce adverse side effects (Vioxx was withdrawn from sale for raising heart risks).
To date, the effects of blueberries on human arteries have not been tested.
That said, humans and rats share highly similar artery control mechanisms, so it seems reasonable to expect that ample amounts of berries could also relax people’s arteries.
The blueberries used in the study were provided by the Wild Blueberry Association of North America.
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Kristo AS, Kalea AZ, Schuschke DA, Klimis-Zacas DJ. A wild blueberry-enriched diet (Vaccinium angustifolium) improves vascular tone in the adult spontaneously hypertensive rat. J Agric Food Chem. 2010 Nov 24;58(22):11600-5. Epub 2010 Oct 22.
Nicholson SK, Tucker GA, Brameld JM. Effects of dietary polyphenols on gene expression in human vascular endothelial cells. Proc Nutr Soc. 2008 Feb;67(1):42-7. Review.
Plotnick GD, Corretti MC, Vogel RA, Hesslink R Jr, Wise JA. Effect of supplemental phytonutrients on impairment of the flow-mediated brachial artery vasoactivity after a single high-fat meal. J Am Coll Cardiol. 2003 May 21;41(10):1744-9.
Sánchez M, Galisteo M, Vera R, Villar IC, Zarzuelo A, Tamargo J, Pérez-Vizcaíno F, Duarte J. Quercetin downregulates NADPH oxidase, increases eNOS activity and prevents endothelial dysfunction in spontaneously hypertensive rats. J Hypertens. 2006 Jan;24(1):75-84.
- Suzuki A, Yamamoto N, Jokura H, Yamamoto M, Fujii A, Tokimitsu I, Saito I. Chlorogenic acid attenuates hypertension and improves endothelial function in spontaneously hypertensive rats. J Hypertens. 2006 Jun;24(6):1065-73.