Blueberries

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

HPhytonutrient Richness from Blueberries

Part of what provides blueberries with their spectacular flavors, aromas, and colors is their unique combination of phytonutrients. These berries provide us with 260-460 milligrams of total phenols in just two-thirds of one cup and at a cost of only 50-60 calories. Many of these phenols come in the form of flavonoids. Within this flavonoid group, blueberries provide us with flavonols like quercetin, myricetin, and kaempferol. But blueberries are best known for their anthocyanin flavonoids. Included in this anthocyanin list are cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin. Up to one third of all phenolic compounds in blueberries can consist of flavonoids.

In addition to other phytonutrients including phenolic acids and carotenoids, blueberries provide us with two unique anti-inflammatory and antioxidant phytonutrients belonging to the group of compounds known as stilbenoids. These two members of the stilbenoid family are resveratrol and pterostilbene. Resveratrol is the better known of these two stilbenoids due to a good bit of publicity about its concentration in red wine. (Red wine gets its resveratrol from the skin of red grapes.) Blueberries do contain resveratrol, yet in much smaller amounts than red wine. However, blueberries do have a strong suit in this stilbenoid category of phytonutrients, and that strong suit is pterostilbene.

You may sometimes hear stilbenoids being referred to as "phytoalexins." This name describes a group of molecules that can be synthesized by plants in response to the threat of infection by bacteria, other microbes, or environmental stressors. Because of their antioxidant, anti-inflammatory, and antimicrobial properties, stilbenoids like resveratrol and pterostilbene are a perfect fit in plant defense systems.

Pterostilbene has been shown to display many of the same properties as resveratrol in recent studies. It not only acts as an anti-inflammatory and antioxidant nutrient, but it also has antidiabetic, cardioprotective, neuroprotective, and chemopreventive (anti-cancer) properties. (Resveratrol has been shown to have all of these same properties.) Recent studies have shown that pterostilbene may be more bioavailability than resveratrol when we eat foods, including blueberries, that contain both stilbenoids. One study has shown pterostilbene to spend as much as five times longer in our body (once absorbed) before being metabolized into other compounds. This longer-lasting nature of pterostilbene may give it more time to provide us with its many health benefits. It's worth noting here that pterostilbene is present in grape plants as well as blueberries, but unlike its presence in the blueberries themselves, pterostilbene it is found primarily in the vine portion of the grape plants rather than the grapes.

The list below provides a summary of key photonutrients provided to us by blueberries:

  • Anthocyanins

    • malvidins

    • delphinidins

    • pelargonidins

    • cyanidins

    • peonidins

    • petunidin

  • Hydroxycinnamic acids and derivatives

    • caffeic acids

    • ferulic acids

    • coumaric acids

  • Hydroxybenzoic acids and derivatives

    • gallic acids

    • protocatechuic acids

  • Flavonols

    • kaempferol

    • quercetin

    • myricetin

  • Flavan-3-ols

    • catechin

  • Stilbenoids (phytoalexins)

    • pterostilbene

    • resveratrol

Other Potential Health Benefits from Blueberries

With a nutrient-rich fruit like blueberries, we would typically expect to be present you with a list of chronic diseases and clear evidence for the ability of blueberries to decrease risk of those diseases when enjoyed in an everyday meal plan. Several research limitations prevent us from providing you with such a list, even though we are confident that we will eventually be able to do so. What we can tell you with certainty is where the research stands at present.

In the area of cardiovascular problems, the best research we've seen shows a consistently favorable impact of blueberry consumption on blood pressure, especially in persons with already elevated blood pressure. Participants in most of these studies have consumed blueberries in the form of freeze-dried blueberry beverages rather than blueberries in their fresh form. In general, however, we simply don't have a sufficient number of human studies in this cardiovascular area to document blueberry benefits. Although we would expect the unique collection of antioxidant and anti-inflammatory phytonutrients found in blueberries to provide cardiovascular benefits well beyond blood pressure regulation (including decreased risk of atherosclerosis), we need large-scale human studies to document these benefits. We also need studies on the consumption of whole, fresh blueberries as well as studies that analyze low, medium, and high intake of blueberries among healthy persons. And finally, we need studies that look specifically at blueberries rather than lumping them together with other berries.

Animal research on blueberries and cardiovascular problems provides us with more definitive results. In animal studies, blueberry extracts have fairly consistently shown an ability to decrease risk of oxidative stress and unwanted inflammation in blood vessels. And like human studies, animal studies have also shown blueberry extracts to have favorable effects on blood pressure regulation.

In the area of blood sugar regulation, a fairly substantial number of animal studies have looked at intake of blueberry extracts (or isolated blueberry phytonutrients) on blood sugar levels, insulin secretion, insulin resistance, and insulin sensitivity. For the most part, the results have shown improved insulin sensitivity, decreased insulin resistance, and improved blood sugar levels following intake of extracts by rats and mice. However, benefits have not been shown in all animal studies. The best studies that we have reviewed on human consumption of blueberries haven't focused on blueberries per se but have included them among other fruits. In one of these studies, blood sugar regulation was improved through consumption of three low-GI (glycemic index) fruit servings per day. While we are encouraged by this result, we would still like to see blood sugar-related studies that focused specifically on blueberries.

In this context of glycemic index, we would also like to note that blueberries are classified as a low-GI fruit based on studies showing their GI value to fall between 40-53. (At WHFoods, we consider all foods to be low GI if their glycemic index value falls at 55 or below.) Blueberries also rank as a good source of fiber, providing about 3.5 grams per fresh cup. When you combine their low GI value with their ability to provide us with a good amount of fiber, it should not be surprising that blueberries might help us improve our blood sugar regulation, even though they have enough sweetness to feel like a delicious treat.

Two other health research areas are important to mention with respect to blueberries. The first involves cognitive function. Preliminary studies have shown an ability of blueberry intake to improve nervous system responses, most likely by helping to protect nerve cells from oxidative damage. In one study involving older adults (with an average age of 76 years), 12 weeks of daily blueberry consumption was enough to improve scores on two different tests of cognitive function including memory. While participants in the study consumed blueberries in the form of juice, three-quarters of a pound of blueberries were used to make each cup of juice. When converted into cups, this amount represented between 2 and 2-1/2 cups per day. While this amount is likely to be more than most people would consume on a daily basis, it is still encouraging to see improvement in cognitive function (including memory) being linked to intake of blueberries in food form. We would also like to note that improved neural responses following intake of blueberry extracts has been shown in several animal studies. In addition, decreased impact of reactive oxygen species (ROS) on the central nervous system has been observed in animal studies involving intake of blueberry extracts.

A final area of health research we want to touch on is research on cancer risk. Both of the stilbenoids present in blueberries—pterostilbene and resveratrol—have been shown to have chemoprotective (cancer-preventing) and tumor suppressing properties. In addition, we know that the combination of chronic oxidative stress and chronic low level inflammation can increase the likelihood of cancer initiation. This unwanted combination leaves blueberries in a very likely position to lower cancer risk by supplying us with a unique combination of antioxidant and anti-inflammatory phytonutrients. Lab studies on several cancer cell lines have already shown the ability of blueberry extracts to inhibit proliferation (increase in cancer cell numbers) and to induce apoptosis (cell death) in several cancer cell types. This area of blueberry intake and decreased cancer risk is one we expect to see gaining attention in future research studies.

Contacts

mail@doforothers.org

Socials
Subscribe to our newsletter

(203) 545-7857