Humans have an intimate connection with grapes, with commercial grape production dating back to 1000 BC. Hundreds of species and varieties of grapes exist, varying in colour, flavour, mouthfeel, chemistry and growing region. The majority of the health benefits associated with the consumption of grape products have been attributed to a diverse class of phytochemicals, including anthocyanins and stilbenes (resveratrol and piceid), two classes of phenolics that reside primarily in the skin, and other flavonoid compounds including quercetin, rutin, catechin and kaempferol.1,2

The antioxidant effects of grapes carry through when individuals with coronary artery disease consume Concord grape juice. In one study, 15 patients with coronary artery disease who drank 4ml/kg body weight Concord grape juice twice daily for two weeks found a significant blunting of copper-mediated LDL oxidation.2 Eleven of the 15 subjects were also taking vitamin E (200 ­ 400IU/day) and 10 were taking vitamin C (500 ­ 1,000mg/day), two antioxidants that also delay the rate of LDL oxidation.3 Concord grape juice further protected against LDL oxidation beyond that seen with the antioxidant supplementation alone.

This same researcher also found a single large serving (12ml/kg) produced the same percentage reduction in platelet aggregation as a single serving of French red wine (5ml/kg), with white wine being ineffectual.4

In the study above, where 14 days of Concord grape juice reduced LDL oxidation, researchers noted significant improvements in dilation of the large brachial artery induced by flow (following removal of an inflated blood pressure cuff) or the use of nitroglycerin, a nitric oxide-donating drug.2 A recent animal study showed that feeding rats a freeze-dried extract of red, green and blue-black California table grapes (both seeded and seedless varieties) rendered their hearts much resistant to heart insult caused by ischemia.5

Using the same preparation, but assessing the effects of chronic dosing (twice/day for 21 days) of 36g (added to 100ml water; equivalent to 1.25 cups of fresh grapes) in healthy normal subjects, resulted in marked increases in blood total antioxidant activity and endothelial cell function following a high-fat meal.6 No alterations were noted in any blood lipid parameters. Men with high systolic hypertension (>132mm Hg) receiving a Concord grape juice beverage averaging 340 ml/day for 12 weeks showed a significant drop after eight and 12 weeks of consumption, compared with a group receiving a placebo beverage with the same calorie load.7 Men receiving Concord grape juice for two weeks (10ml/kg body weight/day) displayed equivalent increases in blood antioxidant measures to those seen in men supplemented with 400IU natural alpha-tocopherol/day.8 However, only in the grape juice group were increases seen in blood triglycerides (probably from increased sugar content in the juice) and decreases in protein oxidation markers.

Another potential concern is reduced iron bioavailability. A recent in vitro study using a cell line designed to mimic the human intestine (Caco-2 cells) showed that red grape juice can potently reduce iron bioavailability.9 Despite these concerns, grape juice and its dried derivatives may prove to be highly functional cardioprotective bioactives for both food and beverage utility.

Anthony Almada, MSc, is the president and chief scientific officer of IMAGINutrition Inc and has been a co-investigator on more than 60 randomised controlled trials.
www.imaginutrition.com

References

1. Demrow HS, et al. Administration of wine and grape juice inhibits in vivo platelet activity and thrombosis in stenosed canine coronary arteries. Circulation 1995;91:1182-8.

2. Stein JH, et al. Purple grape juice improves endothelial function and reduces the susceptibility of LDL cholesterol to oxidation in patients with coronary artery disease. Circulation 1999;100:1050-1055.

3. Heller FR, et al. LDL oxidation: therapeutic perspectives. Atherosclerosis 1998;137 Suppl:S25-31.

4. Folts JD. Antithrombotic potential of grape juice and red wine for preventing heart attacks. Pharm Biol 1998;36:21-27.

5. Cui J, et al. Cardioprotection with grapes. J Cardiovasc Pharmacol 2002;40:762-9.

6. Chaves AA, et al. Vasoprotective effects of a standardized grape product in humans. FASEB J 2003;17:Abstr. 154.2.

7. Mark D, Maki KC. Concord grape juice reduces blood pressure in men with high systolic blood pressure. FASEB J 2003;17:Abstr. 693.10.

8. O'Byrne DJ, et al. Comparison of the antioxidant effects of Concord grape juice flavonoids and alpha-tocopherol on markers of oxidative stress in healthy adults. Am J Clin Nutr 2002;76:1367-74.

9. Boata F, et al. Red grape juice inhibits iron availability: application of an in vitro digestion/Caco-2 cell model. J Agric Food Chem 2002;50:6935-8.