The abundant polyphenols found in berries deliver numerous health benefits
Of all fruits, the consumption of fresh berries is something we oft seek out more than their somewhat more boring apple or banana counterparts. Whether it be berry smoothies; berry cobblers, pies, or crisps; homemade berry wines; or simply fresh berries eaten by the handful when purchased at the farmer’s market – we all probably can remember the last fresh berry product we consumed, which are found abundantly in restaurants and groceries and picnics in the summer.
Berries are excellent sources of polyphenols. Polyphenols are antioxidant compounds that are considered secondary metabolites of plants.[1] They serve to protect the plants in which they are found from environmental challenges including the damaging rays of the sun, insects, disease, and other possible threats to their survival.
More than 8,000 different polyphenols are found in the plant species we consume as food or use medicinally.[1],[2] Although some of these compounds have similar effects in the body due to their related structures, the fact that they are so numerous sheds light on the importance of eating a whole foods diet that provides a rainbow of natural colors. Nature’s colorful rainbow is produced by the interactions of light with the polyphenols and other phytonutrient compounds found within the flora abundant on our earth.
Herein, we take a closer look at the beneficial effects of berry polyphenols on health, with a focus on immunity.
The beneficial actions of berry polyphenols
Both the seeds and skins of grapes and berries are rich in polyphenols including gallic acid, catechin, and epicatechin (which we also find at high levels in green tea), as well as quercetin.
Grapes (which are technically a berry, although we oft consider them as their own subset of fruit) bring us high levels of the well-known polyphenol resveratrol, found primarily in the grape skin.[3] Grape seeds and skin, including the products remaining after the processing associated with wine or juice, have a very high antioxidant capacity, making this a valuable byproduct for potential use in animal feed or the supplement industry.[4],[5] Both the seeds and skins of grapes and berries are rich in important procyanidins and proanthocyanidin members of the polyphenol family including gallic acid, catechin, and epicatechin (which we also find at high levels in green tea), as well as quercetin.[6],[7]
Both animal and human studies have shown enhanced antioxidant status and reduced levels of inflammation with grape seed extract supplementation.[8],[9],[10],[11],[12] In animals, grape seed extract products have been shown to benefit the brain, reducing inflammation, amyloid-β accumulation, and the impact of age on various markers of antioxidant status.[13],[14] In humans, we see their benefits on metabolic health elucidated in a 2020 systemic review and meta-analysis of randomized controlled trials, finding they positively impact fasting glucose, cholesterol balance, and inflammation.[15]
Grape seed extracts have been shown to benefit the brain, reducing inflammation, amyloid-β accumulation, and the impact of age on various markers of antioxidant status.
These are not the only benefits of berry polyphenols – we also find these potent antioxidants with prebiotic potential have a positive impact on immune function and gastrointestinal health.[16] The addition of berry extract products to the diet of animals has been shown to enhance levels of protective immunoglobulins and the response to vaccinations,[9],[17],[18],[19] increase levels of healthy gastrointestinal flora (including lactobacilli and bifidobacteria), and reduce intestinal inflammation as well as levels of potentially pathogenic bacteria.[16]
Clinical studies with berry polyphenols
In a randomized double-blind, placebo-controlled trial of elderly individuals, supplementation with a wolfberry-enhanced milk product significantly improved the vaccination response.
Positive effects on immune function, wellbeing, and gut health have also been seen clinically, particularly in the elderly, in studies with berry or berry polyphenol supplementation. In a randomized, double-blind, placebo-controlled trial (RDBPCT) of older individuals ranging in age from 55 to 72, intake of a boxthorn berry product was shown to significantly increase numbers of lymphocytes (within normal ranges) and IgG levels.[20] Significant improvements were seen in overall feeling of well-being, which included sub-parameters of dizziness, fatigue, and sleep, while a trend of improvement was also seen in short-term memory and focus. In another RDBPCT of elderly individuals (age 65 to 70), supplementation with a wolfberry-enhanced milk product significantly increased influenza-specific IgG levels and seroconversion rate after influenza vaccination.[21]
In humans, regular intake of 100% grape juice has also been observed to be beneficial. 100% grape juice consumption was associated with increased levels of γδ-T cells (which function as a bridge between the innate and adaptive immune response[22]) as well as vitamin C levels.[23] Human consumption of a cranberry polyphenol blend has also been shown to significantly increase proliferation of γδ-T cells (observed in a cell culture) compared to placebo, which was accompanied by a significant reduction in cold and flu symptoms in the individuals taking the polyphenol blend.[24] Intake of berry-derived preparations has also been shown to increase levels of lactobacilli and bifidobacteria in the human gut.[16]
Given that we consume between 200 to 300 mg of polyphenols per 100 g of commonly consumed fresh fruits, dietary intake can be substantial in a diet with a high level of fruit and vegetable intake.[1],[2] Although supplementation always is an option, the studies discussed herein pointedly remind us: don’t forget to eat your fruits and vegetables!
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