Health Benefits of Grapes
Author: Winston Craig, MPH, PhD, RD.
Grapes are native to the Mediterranean region and Central Asia. They grow in clusters on a deciduous woody vine, Vitis vinifera, and come in many colors. Blue, red, purple, black, golden, and green are the most common. The original grapes were red, and the dark grapes all contain a rich supply of anthocyanins, the antioxidant polyphenolic that conveys many health-promoting properties of grapes. Grapes rank with blueberries and blackberries as excellent sources of antioxidants.
Good News from the Grapevine
Grapes can be eaten fresh or dried (raisins), while grape juice is a favorite beverage. Although seedless grapes are highly sought after for table grapes, the absence of seeds does diminish the phytochemical content of the grape. Grapes are also used for making jam, jelly, and wine.
Currants are dried Zante grapes, but the name currant has also been applied to two berries, black currants and red currants, that are unrelated to grapes. Sultanas were originally raisins derived from a lighter grape of Turkish origin.
Grape seeds provide an edible oil. Grape seed extract is also available as a supplement. It is claimed to strengthen capillary walls, so that it finds use in the treatment of venous insufficiency, and edema following surgery. It also reduces the risk of blood clots.
Many of the health benefits attributed to red/purple grapes are due to the pigments that are concentrated largely in the skin and seeds, which have about 100 times higher level than the pulp of the grape. Anthocyanins tend to be the main polyphenolics in red grapes while the catechins are the more abundant phenolic in white grapes. The phenolic content of grape skins depends upon the variety, the soil, climate, geography, cultivation practice, and exposure to fungal infections. Grapes are also rich in ellagic acid, a potent flavonoid that helps fight cancer.
Grapes and grape juice function in different ways in the cardiovascular system. The pigments in red, purple and black grapes protect the cardiovascular system by a number of mechanisms that include the suppression of blood clots, inhibition of LDL cholesterol oxidation, reduced homocysteine levels, and anti-atherosclerotic properties. Grapes stimulate endothelial nitric oxide production which induces relaxation of the blood vessel walls, and a reduction in blood pressure levels. Recently, it was shown that a Concord grape extract lowered LDL cholesterol, raised HDL cholesterol, and decreased plasma inflammatory biomarkers.
Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a dietary constituent found in grapes exerts a wide variety of pharmacological activities. Resveratrol is as an effective agent for cancer chemoprevention due its ability to block many steps in the carcinogenesis process. Resveratrol contained in red grapes and berries has been shown to inhibit prostate cancer cell growth, induce apoptosis, influence interleukin-6, and exert immuno-modulatory effect on mouse lymphocytic leukemia. One of the possible mechanisms for the protective activity of resveratrol is by down regulation of inflammatory responses. Resveratrol also inhibits the nuclear transcription factor, NFkappaB.
Anthocyanins and proanthocyanidins are two groups of polyphenolics in Concord and similar grape juices. These substances show cancer preventive and anti-proliferative properties and can detoxify the activity of some cancer-causing substances. Concord grape juice can protect healthy breast cells from DNA damage caused by a chemical carcinogen. Grape juice also suppresses the growth and development of breast cancer cells in laboratory animals given chemically induced tumors. The grape juice reduced both mammary tumor size and the number of tumors per animal. The pigments in grape juice also improve immune responsiveness.
Promising data suggests the use of grape juice to promote brain health and delay neurodegenerative diseases. Participants that drank purple grape juice and similar fruit juices three times a week were about 70% less likely to develop Alzheimer's disease. When laboratory animals were fed Concord grape juice they showed significantly improved scores on memory and coordination tests.
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Americans typically eat <1 serving/day of whole grain products. The recommendation is for at least 3 servings/day of whole grains. Four large epidemiological studies all reveal a 25 to 35 percent reduction in risk of coronary heart disease with a regular intake of whole grain products.