The most abundant polyphenols in pomegranate juice are the hydrolyzable tannins called ellagitannins formed when ellagic acid binds with a carbohydrate. Pomegranate ellagitannins, also called punicalagins, are tannins with free-radical scavenging properties in laboratory experiments[36] and with potential human effects.[37]
Punicalagins are absorbed into the human body and may have dietary value as antioxidants, but conclusive proof of efficacy in humans has not yet been shown.[38][39] During intestinal metabolism by bacteria, ellagitannins and punicalagins are converted to urolithins which have unknown biological activity in vivo.[40][41] The different punicalagins present in P. granatum are granatin A and B, punicacortein A, B, C and D, 5-O-galloylpunicacortein D, punicafolin, punigluconin, punicalagin, 1-alpha-O-galloylpunicalagin, punicalin and 2-O-galloyl-punicalin.[citation needed] Other phenolics include catechins, gallocatechins, and anthocyanins, such as prodelphinidins, delphinidin, cyanidin, and pelargonidin.[42] The ORAC (antioxidant capacity) of pomegranate juice was measured at 2,860 units per 100 grams.[43]
Many food and dietary supplement makers use pomegranate phenolic extracts as ingredients in their products instead of the juice. One of these extracts is ellagic acid, which may become bioavailable only after parent molecule punicalagins are metabolized. However, ingested ellagic acid from pomegranate juice does not accumulate in the blood in significant quantities and is rapidly excreted.[44] Accordingly, ellagic acid from pomegranate juice does not appear to be biologically important in vivo.
In preliminary laboratory research and clinical trials, juice of the pomegranate may be effective in reducing heart disease risk factors, including LDL oxidation, macrophage oxidative status, and foam cell formation.[45][46][47] In mice, "oxidation of LDL by peritoneal macrophages was reduced by up to 90% after pomegranate juice consumption...".[48]
In a limited study of hypertensive patients, consumption of pomegranate juice for two weeks was shown to reduce systolic blood pressure by inhibiting serum angiotensin-converting enzyme.[49] Juice consumption may also inhibit viral infections[50] while pomegranate extracts have antibacterial effects against dental plaque.[51]
Despite limited research data, manufacturers and marketers of pomegranate juice have liberally used evolving research results for product promotion, especially for putative antioxidant health benefits. In February 2010, the FDA issued a Warning Letter to one such manufacturer, POM Wonderful, for using published literature to make illegal claims of unproven antioxidant and anti-disease benefits.[52][53][54]
Metabolites of pomegranate juice ellagitannins localize specifically in the prostate gland, colon, and intestinal tissues of mice,[55] leading to clinical studies of pomegranate juice or fruit extracts for efficacy against several diseases.
In 2011, 32 clinical trials were registered with the National Institutes of Health to examine effects of pomegranate extracts or juice consumption on a list of diseases:[56]
- prostate cancer
- prostatic hyperplasia
- diabetes
- lymphoma
- rhinovirus infection (completed, July 2008)
- common cold (completed, June, 2007)
- oxidative stress in diabetic hemodialysis
- atherosclerosis
- coronary artery disease
- infant brain injury
- hemodialysis for kidney disease
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