Basket of new studies adds more evidence of their potent health powers 08/29/2019
Evidence that antioxidant-rich fruits and vegetables aid basic aspects of human health abounds.
We covered a good deal of berry-related research in reports you'll find in the Berries & Fruits section of our news archive.
And a basket of new blueberry studies significantly boosts evidence that their flavonoid-type antioxidants — which occur in all berries — bring real vascular and brain benefits.
We’ll take a quick look at four new blueberry studies that confirmed brain and vascular benefits, and review another recent study that linked strawberries to better brain performance.
Finally, we will summarize what flavonoids are, where they’re found, and the benefits of each of the six types, which are concentrated in different groups of plant foods.
Blue versus gray: Studies find brain and vascular benefits
Four new blueberry studies were presented at a symposium titled “Blue versus Gray: Potential Health Benefits of Blueberries for Successful Aging.”
All four studies appeared in The Journals of Gerontology and were accompanied by an editorial from Donald K. Ingram, Ph.D., of Louisiana State University’s Pennington Biomedical Research Center.
Dr. Ingram noted that the new findings echo a growing body of pro-blueberry evidence: “Since the 1990s, research on the health benefits of blueberries has grown exponentially. Studies have documented that this fruit ranks highest in antioxidant activity compared to many other popular fruits … [and]… other mechanisms for the health benefits of blueberries, such as their anti-inflammatory properties, have been identified.”
Study #1: French clinical trial sees memory benefits
A French team led by Dr. Veronique Pallet conducted a randomized, double-blind, placebo-controlled trial among 215 volunteers who ranged from 60 to 70 years of age (Bensalem J et al. 2019).
The participants in this six-month trial were divided into two groups one of which took daily capsules containing a grape-blueberry extract (258mg flavonoids per capsule), while the control group took placebo capsules daily.
The volunteers underwent periodic brain-performance tests designed to test various aspects of their learning and memory capacities.
Although the results didn’t find that every aspect of brain performance tested improved the blueberry group, the researchers detected specific memory benefits in the blueberry group.
Interestingly, those benefits were most pronounced in people with the highest levels of flavonoids called flavan-3-ols, which are relatively uncommon, but especially abundant in blueberries, non-alkalized cocoa, and in OPC (grape seed and maritime-pine bark) supplements
Study #2: Rat maze test reveals memory benefits
Famed antioxidant researcher Dr. Barbara Shukitt-Hale’s team conducted maze tests that showed, compared to rats on a control diet, improved memory performance among aged rats that received supplemental blueberries (Shukitt-Hale B et al. 2019).
Study #3: British evidence review confirms blueberries’ brain benefits
Dr. Claire Williams of King’s College London led a team that reviewed the evidence from 11 clinical trials. They found that, overall, the trials provided good evidence that blueberries improve memories in children and boost brain performance among older adults suffering from mild cognitive impairment. (Hein S et al. 2019)
(You may be interested in our 2012 report on related research, titled Berries' Brain Benefits Affirmed, Expanded.)
Study #4: British evidence review confirms blueberries vascular benefits
A team led by Dr. Anna Rodriguez, also of King's College London, published an evidence review in which they concluded that blueberries exert beneficial vascular effects, including dilation (opening) of blood vessels (Rodriguez-Mateos A et al 2019).
The authors of the study reported that people who consumed 200 grams (about 1 cup) of blueberries daily enjoyed healthier blood vessel function and lower systolic blood pressure.
Importantly, the authors of that study gave credit to anthocyanins — the flavonoids that give blueberries their dark color.
Strawberries linked to better memories
Chicago’s Rush University has become a center for research on nutrition and the brain.
We’ve reported on several Rush studies, many led by professor Martha Clare Morris, exploring the brain-health effects of the Mediterranean diet and others — including the MIND diet developed at Rush.
In animal studies, strawberries’ antioxidant and anti-inflammatory properties improve brain cell function, cognition and motor (movement) function.
Those findings prompted Dr. Morris to co-author a study published last June, whose results linked higher strawberry intakes to reduced risk for Alzheimer’s disease.
Her new study involved 924 volunteers — average age 81 years, average education level 15 years — who answered to diet surveys and underwent two annual neurological evaluations.
The authors’ analysis revealed that — compared with people who ate no strawberries — the people who reported eating strawberries more than once a week were 32% less likely to develop Alzheimer's.
Importantly, the results accounted for the known brain-health effects of age, sex, education, physical activity, participation in cognitive activities, presence of the APOE- ɛ4 gene variation (which predisposes people to Alzheimer’s), total daily calorie intake, intakes of other fruits, and intakes of green leafy vegetables.
The likely source of berries’ benefits? Antioxidants in the flavonoid family
Most of the antioxidants in the average American’s diet are polyphenols from plant foods.
Coffee is the biggest single source of antioxidants — including flavonoids — in the diets of most Americans, and in countries where people drink more coffee than tea.
While flavonoids abound in most whole plant foods, tests repeatedly rank blueberries as the richest food source by weight — and wild blueberries have significantly more flavonoids than cultivated ones.
Most of the polyphenols in the American diet are flavonoids, which fall into six distinct categories: flavonols, flavanols, flavan-3-ols, flavanones, flavones, anthocyanins, and isoflavones.
Each of these subgroups of flavonoids appears to offer different but overlapping benefits, which underscores the wisdom of eating a wide variety of plant foods:
- Flavones occur in celery, parsley, various culinary herbs, and hot peppers. They’re associated with overall antioxidant benefits.
- Anthocyanidins: The best sources include red, purple and blue berries; pomegranates; plums; red wine; and red and purple grapes. Anthocyanidins appear to support heart health and may help discourage obesity and diabetes.
- Flavonones: Citrus fruits are the richest sources of these antioxidants which are associated with cardiovascular health, and general antioxidant and anti-inflammatory effects.
- Isoflavones: Top sources include soybeans and other legumes. They mimic the female hormone estrogen, and mixed evidence suggests that they may help lower the risk of estrogen-dependent cancers, such as breast, endometrial, and prostate cancers.
- Flavonols abound in onions, leeks, Brussels sprouts, kale, broccoli, tea, berries, beans and apples. Quercetin is a common, powerfully anti-inflammatory flavonol that helps prevent inflammation-related conditions like heart disease and dementia, but also exerts antihistamine effects that may ease hay fever symptoms.
- Flavanols are most concentrated in teas, cocoa, grapes, apples, berries, fava beans, and red wine. They appear to aid cardiovascular and neurological health and may offer some anti-cancer benefits.
- Agarwal P et al. Strawberry Consumption Associated with Reduced Alzheimer's Dementia Risk (FS05-06-19). Current Developments in Nutrition, Volume 3, Issue Supplement_1, June 2019, nzz052.FS05-06-19, https://doi.org/10.1093/cdn/nzz052.FS05-06-19
- Bensalem J, Dudonné S, Etchamendy N, et al. Polyphenols from grape and blueberry improve episodic memory in healthy elderly with lower level of memory performance: a bicentric double-blind, randomized, placebo-controlled clinical study [published online ahead of print July 19, 2018]. J Gerontol A Biol Sci Med Sci. 2019;74:996–1007. doi:10.1093/gerona/gly166
- Bondonno NP et al. Flavonoid intake is associated with lower mortality in the Danish Diet Cancer and Health Cohort. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-11622-x
- Hein S, Whyte A, Wood E, Rodriguez-Mateos A, Williams C. Systematic review of the effects of blueberry on cognitive performance as we age [published online ahead of print April 3, 2019]. J Gerontol A Biol Sci Med Sci. 2019;74:984–995. doi:10.1093/gerona/glz082
- Rodriguez-Mateos A, Istas G, Boschek L, et al. Circulating anthocyanin metabolites mediate vascular benefits of blueberries: insights from randomized controlled trials, metabolomics, and nutrigenomics [published online ahead of print February 16, 2019]. J Gerontol A Biol Sci Med Sci. 2019;74:967–976. doi:10.1093/gerona/glz047
- Shukitt-Hale B, Thangthaeng N, Miller MG, Poulose SM, Carey AN, Fisher DR. Blueberries improve neuroinflammation and cognition differentially depending on individual cognitive baseline status [published online ahead of print February 17, 2019]. J Gerontol A Biol Sci Med Sci. 2019;74:977–983. doi:10.1093/gerona/glz048