Most supplements have certain benefits and certain side effects. You may already know about the benefits of resveratrol and this article highlights the potential side effects of resveratrol. We first review the information about resveratrol side effects circulated over the internet and then we review a few scientific articles about its side effects.
Resveratrol Side Effects One top-ranked website in Google says, overdosage of resveratrol may lead to tendinitis pain, but the side effects vary from person to person depending on the physical attributes of the users. The website further says resveratrol can work as a blood-thinner. Faulty consumption of resveratrol may lead to insomina, joint ache, diarrhea, stomach pain, colored urine, flu and acne.
Another top-ranked website in Google says, intake of resveratrol can lead to an increase in blood pressure. Wait a minute, the previous website says resveratrol is a blood-thinner?? This website further says resveratrol side effects include a buzzed feeling, insomnia, stomach cramping and diarrhea.
Linus Pauling Institute, Oregan State University says, resveratrol is not known to cause adverse effects in humans. A single dose up to 5 grams led to no serious side effects. Linus Pauling Institute suggests patents with hormone-related cancers should avoid resveratrol supplements. It is unclear how the estrogenic activities affects the cancers. _______________________________________________________________________
Resveratrol Side Effects - Scientific Articles
Resveratrol may lead to three side effects, based on research findings:
1. Hinderance of metal absorption The first potential resveratrol side effect is a speculation based on its anti-cancer mechanism. In a study of 2005, plasmid bluescript SK(+) DNA was treated with increasing concentrations of resveratrol in the presence and absence of copper ions, transformed into competent DH5alpha cells and sequenced. The study shows a decrease in the transformation efficiency of the plasmid after resveratrol treatment, and although all types of mutations were recorded, point mutations (deletions/substitutions) were found to be the predominant ones. Resveratrol alone resulted in deletion of mainly guanine bases. In the chromatin of nucleus, copper ions are bound to guanine bases. This study suggests the mobilization of such endogenous copper by resveratrol resulting in prooxidant DNA cleavage at the site. In various cancer cell lines, the copper concentration is reported to be elevated and this study may explain the anticancer activity of resveratrol.  In fact, resveratrol is generally considered as a copper chelator. [4-6]. Thus, it is speculated that oral intake excessive amount of resveratrol orally may hinder the absorption of certain metal ions, especially copper ion, leading to copper deficiency. Please, note that it is not a direct evidence for such side effect.
2. High Doses - Delay of Recovery of Gastric Ulcer The second potential resveratrol side effect is observed from an animal study. Researchers from Dr. B.C. Roy Post Graduate Institute of Basic Medical Sciences & I.P.G.M.E. & R., India., demonstrated the biphasic activity of resveratrol in indomethacin-induced gastric ulcerated mice. They observed a beneficial effect of resveratrol at a low dose (2 mg/kg) but unwanted side effect at a higher dose of resveratrol (10 mg/kg). The lower dose of resveratrol (2 mg /kg) augmented eNOS expression without altering COX-1 expression, but, at a higher dose (10 mg / kg), resveratrol predominantly suppressed COX-1 expression, which significantly reduced both PGE2 synthesis and angiogenesis. It (high dose) ultimately resulted in delay healing of indomethacin-induced gastric ulcers. [1, 2]
3. Drug Interaction Hong SP, Chosun University, Korea, found that intake of resveratrol significantly increased the extent of the absorption (AUC) of diltiazem, except for resveratrol 0.5 mg/kg, in a rat study. The relative bioavailability of diltiazem in the presence of resveratrol (2.5 and 10 mg/kg) was increased by 1.48- to 1.60-fold! Researchers explained that resveratrol significantly increased the bioavailability of diltiazem due to the inhibition of both the cytochrome P450 3A4-mediated metabolism and the efflux pump P-glycoprotein in the intestine and/or liver.  This unwanted side effect can be extremely serious for diltiazem users! It is also speculated that resveratrol may slow down the metabolism of some drugs including statins, statins, erectile dysfunction meds, calcium channel blockers and some immune-system suppressants. That could dangerously screw up the doses. 
4. Cancinogenic? There's some evidence that resveratrol may activate estrogen receptors on cells, spelling side effects or trouble for women with a history of estrogen-sensitive tumours (often breast, ovarian and uterine). 
5. Pimples and Infections Finally, Dr. Gerald Weissmann, director of New York University's biotechnology study center pointed out a possible side effects of resveratrol. In an interview, he said, ""you might get terrible pimples, infections or worse" Resveratrol may set loose in the body to scavenge toxins also function to dampen our defenses against some dangerous bacteria." 
Remarks Most of the potential side effects may happen only when resveratrol is taken at very high doses.
Resveratrol probably may have some other side effects not reported yet. Please, consult with your doctor before taking any supplements. _______________________________________________________________________________________________________________
Different people may experience different side effects and benefits of a product. You are encouraged to report adverse side effects to FDA, its website is www.fda.gov., or report the adverse side effects to the manufacturer, you should be able to find the contact information on the label.
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