Blueberries have long been recognized as a healthy addition to any diet.

They are a good source of vitamin C and manganese as well as dietary fiber and one cup of blueberries is a mere 80 calories. National Nutrient Database for Standard Reference. Release 20 USDA-ARS 2006. But it was the discovery of their antioxidant activity that put blueberries in the headlines in the late '90s.

Blueberries and Antioxidants
Antioxidants are free-radical quenchers, helping protect us against oxidative cellular damage that can lead to the development of cancer, heart disease and degenerating brain function such as Alzheimer's disease. A comprehensive study of the antioxidant capacity of foods, using a test tube assay called ORAC (Oxygen Radical Absorbing Capacity), was conducted by Dr. Ronald Prior and his team of researchers. They reported that blueberries ranked among the highest on the list. (Wu, X. et al. J Agric Food Chem 2004, 52:4026-37.)

The major contributors to this high level of antioxidant activity are a family of compounds in blueberries called polyphenols--particularly the anthocyanins that give blueberries their blue hue. (Prior, R.L. et al J Agric Food Chem. 1998, 46: 2686-93)

While the ORAC antioxidant values cannot tell us how effective individual foods may be in reducing disease-producing oxidative stress, they do provide us with clues. You can find a complete listing of the ORAC values of fruits and vegetables at http://www.ars.usda.gov/Services/docs.htm?docid=15866


Blueberries and Brain Function
The high ORAC antioxidant values inspired many researchers to further investigate the health promoting potential of blueberries. Neuroscientist James Joseph and his team at the USDA Human Nutrition Research Center on Aging in Boston set out to determine whether blueberries protect against age-related decline of brain function. In his landmark study, Dr. Joseph found that aged rats fed blueberry-supplemented diets (equivalent to about 1 cup per day in a human diet) experienced significant improvement in both memory function and motor behavior. Dr. Joseph suspected that the antioxidative properties of the polyphenolic compounds--especially the anthocyanins--contributed to these remarkable findings. When he studied the brain tissues of these animals, however, Dr. Joseph found that the beneficial effects of blueberries could not be explained solely on the basis of the free-radical-quenching antioxidant properties of the polyphenols. (Joseph, J. A. et al. J Neurosci. 1999, 19:8114-21)

Similarly, with a strain of mice that develop Alzheimer's-like symptoms, Dr. Joseph and his team observed that blueberry supplementation resulted in significantly better cognitive and motor performance. They also discovered that in the brains of the blueberry-eating "Alzheimer’s" mice, the levels of certain chemicals responsible for transmitting messages from neuron to neuron were closer to normal than in the untreated "Alzheimer's" animals and that the message receptors on the neurons were better able to receive the signals. Once again, the researchers found that enhanced antioxidant activity could not solely explain the improvements in brain function. (Joseph, J. A. et al. Nutr Neurosci. 2003, 6:153-62)

More recently, Dr Joseph has been studying the anti-inflammatory potential of the polyphenols in blueberries, since chronic inflammation at the cellular level is at the heart of many degenerative age-related diseases. The inflammatory process is extremely complex, controlled by biochemical regulators that can turn it up or turn it down. When rats with neuronal lesions were fed a blueberry-supplemented diet, not only did they perform better in cognitive tests than the controls that were not fed blueberries, the concentration of several substances in the brain that can trigger an inflammatory response was significantly reduced. Apparently the polyphenols in the blueberries were inhibiting the production of these inflammatory mediators. (Lau, F.C. et al., J. Neuroscience Res., 2007, 85:1010-17)

In the treatment of Parkinson's disease, transplantation of dopamine-producing neurons has been used to help offset progressive brain damage. However, the grafted brain cells survive poorly, believed to be the result of their high susceptibility to oxidative stress. In the rodent model, dietary supplementation with blueberry extract for six weeks prior to grafting new dopamine neurons resulted in a two-fold increase in the survival of the implants and improved motor behavior when compared to transplanted animals not receiving blueberries in their diet. (McGuire, S.O., et al. Nutr. Neuroscience, 2006, 9:251-258)


Blueberries and Longevity
A recent study examined the effect of blueberries on lifespan and aging of the simple soil nematode, a microscopic worm used in biologic studies. Researchers were surprised to find that the addition of blueberry extract s ignificantly increased the lifespan of these tiny animals. To understand the mechanism, researchers then fed the nematodes several fractions of the polyphenolic compounds found in blueberries. They discovered that it was the proanthocyanidin fraction protecting against heat stress rather the expected oxidative stress that was responsible for the observed increase in life span. Once again, the explanation went beyond simple antioxidant activity. (Wilson, M. A. et al. Aging Cell, 2006, 5(1): 59-68)


Blueberries and Urinary Tract Health
Several studies conducted at Rutgers University suggest that another polyphenolic compound found in blueberries called proanthocyanidins can inhibit the adhesion of bacteria to the lining of the urinary tract. If the bacteria are prevented from attaching to urinary tract cells, they cannot multiply and cause infections. The blueberry proanthocyanidins are similar to those found in cranberries, which are responsible for prevention of urinary tract infections. Clinical studies are needed to confirm a similar benefit for blueberries. (Schmidt, B.M. et al. J Agric Food Chem. 2004, 52, 6433-42.)