Blueberry's Superfruit Status

By Toby Amidor, R.D., Contributing Editor

As one of the few fruits native to the United States, blueberries are a healthy part of the countrys history. Native Americans gathered fresh blueberries from forests and bogs and used them for food and medicinal purposes. Once the settlers arrived, the Wampanoag Indians taught them how to gather, dry and store blueberries for the long winter months to supplement their cultivated food supply. Civil War soldiers drank blueberry juice in order to prevent scurvy. Today, blueberries have gained a reputation as being a superfruit because of their nutritional benefits.

All about blueberries

The blueberry genus Vaccinium includes over 450 plants, but three varieties are most abundant. The northern highbush (V. corymbosum) grows wild in North American forests, and the bush can reach a height of 15 ft. The lowbush (V. angustifolium), known as wild blueberries, grow on 1- to 2-ft. dwarf bushes and survive in the wild as far north as Arctic North America. Unlike cultivated highbush berries, lowbush blueberries are harvested from wild clones. The southern rabbiteye (V. ashei) thrives in the southern United States.

The North American blueberry season is from April through October; in South America it runs from November through March. This makes blueberries available year-round. About half of the blueberry crop is sold as fresh; the rest are processed into various forms, including frozen, dried, and liquid juices and purees.

Superfruit nutrient stats

Cultivated blueberries contain approximately 57 calories per 100 grams, no fat, only 1 mg sodium, and provide 2.4 grams fiber.  They are an excellent source of vitamin C (9.7 mg per 100 grams). Wild blueberries are smaller than the cultivated highbush varietiesapproximately 1,600 wild blueberries in a pound, compared with around 500 cultivatedso they tend to be more nutrient-dense. One of the most notable differences is that wild blueberries contain more than eight times more manganese per 100 grams than cultivated blueberries. Wild varieties also have 25% fewer calories.

Blueberries rank among the highest in ORAC (oxygen radical absorption capacity) value at 2,400 per 100 grams and, in addition to vitamin C, contain a number of phytochemicals, such as phenolic acid, anthocyanins, proanthocyanidins and ellagic acid; the latter is linked to inhibiting tumor growth (Nutrition and Cancer, 2008; 60(2):227-234). According to the "USDA Database for the Flavonoid Content of Selected Foods," they contain the following average flavonoid amounts: the anthocyanins cyanidin (15 mg per 100 grams), delphinidin (30 mg per 100 grams), malvidin (49 mg per 100 grams), peonidin (7 mg per 100 grams), petunidin (12 mg per 100 grams); the flavan-3-ol epicatechin (1.11 mg per 100 grams); and the flavonols myricetin (0.82 mg per 100 grams) and quercetin (3.11  mg per 100 grams). Anthocyanins give blueberries their deep-blue color and are a major contributor to their antioxidant activity. Procyanidins (catechin and epicatechin, and a series of oligomers) make up to 32% of blueberries total ORAC.  Fresh and frozen blueberries contain the highest amounts of anthocyanins; little is found in the dried form. A study published in the Journal of Agriculture and Food Chemistry in 2006 (54(11):4,069-4,075) found anthocyanins were highest in fresh and frozen berries, but were almost undetectable in processed foods. The fresh highbush (cultivated) contain 125 mg anthocyanins per 100 grams. Proanthocyanidins, or condensed tannins, are polymers of flavan-3-ols, and contribute an astringent flavor.

A 2000 study published in the Journal of Food Science (65:357-364) looked at changes in blueberry anthocyanins and polyphenolics during processing into juice and concentrate. Results indicated that only 32% of the anthocyanins were found in the single-strength juice, with 18% left in the press-cake residue.

Studying health benefits

Northeast Native American tribes relied on blueberries for their medicinal effects. They thought tea made from blueberry leaves was good for the blood, and used blueberry juice to treat coughs. Today, extensive studies indicate that blueberries and blueberry ingredients might play a role in reducing risk of cancer, cardiovascular disease and urinary tract infections, and improving memory and cognitive function.

Several blueberry phytochemicals may help protect against various forms of cancer. A 2006 study in the Journal of Agricultural and Food Chemistry (54(25):9,329-9,339) found the phenolic compounds in blueberries were most effective against prostate cancer cells and inducing cell death of colon cancer cells. A study published in 2005 in the same journal concluded that phenolic compounds found in blueberries inhibited the growth of colon cancer cells in vitro and induced cancer cell death (53(18):7,320-7,329). A 2001 in vitro study published in the Journal of Medicinal Food (4:49-51) concluded that blueberry extracts inhibited cervical and breast cancer cells.

Several studies have also suggested that blueberries may play a role in heart health and helping prevent urinary tract infections. A 2008 study in the British Journal of Nutrition (100(1):70-78) linked blueberry supplementation in pigs to reduced plasma cholesterol levels. A 2002 study in Nutritional Neuroscience concluded that the consumption of blueberries may protect the brain against damage from ischemic strokes (5(6):427-431). A study published in 2004 in The Journal of Agricultural and Food Chemistry (52(21):6,433-6,442) found that blueberries contain the same compounds as cranberries that prevent the growth of bacteria responsible for urinary tract infections.

Studies of older laboratory animals consuming blueberry supplements have shown measurable improvement in memory and cognitive function. A 2007 study published in the Journal of Neuroscience Research (85(5):1,010-1,017) found that blueberry extract inhibited various markers of CNS inflammation, such as nitric oxide, cytokines interleukin-1B and tumor necrosis factor-a. A second study, published in 2008 in Neurobiology of Aging (29(11):1,680-1,689), found that rats fed a diet containing 2% blueberry extract and treated with kainic acid exhibited less impaired learning performance than rats treated with kainic acid alone, based on performance variables using a T-maze. A third study, published in April 2005 in Nutritional Neuroscience (8(2):111-120), found a relationship between performance of aged rats in the Morris water maze and the total number of anthocyanin compounds found in the cortex of the rats.

Another potential blueberry benefit might be for obesity and diabetes. A 2009 study published in the International Journal of Obesity (33:1,1661,173) studied the effects of juice extract from lowbush blueberries biotransformed with bacteria from the skin of the fruit. This juice decreased hyperglycemia in diabetic mice and protected prediabetic mice from developing obesity and diabetes.

Toby Amidor is a registered dietitian with 10 years experience in the field as a culinary school educator, food safety consultant and clinical practitioner. She has consulted for various online sites and is currently the nutrition expert for FoodNetwork.com. She can be reached at [email protected].

Photo: U.S. Highbush Blueberry Council