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Researchers in Italy analyzed 14 brands of resveratrol pills and found only 5 that met their labeled value for dosage.  The brands were not identified.

The difference between the labeled and actual dose may be attributed to degradation of the molecule.  The active form of this molecule (trans resveratrol), degrades to its less active form (cis resveratrol) upon exposure to light.  Heat and oxygen (oxidation) can also degrade resveratrol.  Light exposure actually “isomerizes” resveratrol into a different molecule — trans to cis.

Indeed, the researchers tested for cis resveratrol and found it was prevalent in many of the mislabeled brands, which suggests the product may have been exposed to environmental factors during extraction from a botanical source, during manufacturing, or possibly during shipping of shelf storage.

Only a few resveratrol pills are made (micro-encapsulation) or packaged (opaque shell) to protect from light degradation.

The authors of the study below found the pure synthetic form of resveratrol performed better than botanically-derived extracts (giant knotweed, grape), but purity is no guarantee resveratrol will not be subject to degradation.

The resveratrol products were also put to a lab dish test and only 3 of 14 brands adequately inhibited cell growth (i.e cancer), one of its well-touted benefits.

Readers can view the full text of the study by clicking here.   Copyright 2012 Bill Sardi, ResveratrolNews.com

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Molecules. 2012 Oct 22;17(10):12393-405. doi: 10.3390/molecules171012393.

trans-Resveratrol in Nutraceuticals: Issues in Retail Quality and Effectiveness.

Rossi D, Guerrini A, Bruni R, Brognara E, Borgatti M, Gambari R, Maietti S, Sacchetti G.

Source

Dipartimento Scienze della Vita e Biotecnologie-SVEB, UR7 Terra&Acqua Tech-Università di Ferrara, Corso Ercole I d’Este 32, 44121 Ferrara, Italy. renato.bruni@unipr.it.

Abstract

Fourteen brands of resveratrol-containing nutraceuticals were evaluated in order to verify their actual resveratrol content and to control if their health-promoting properties are related to manufacturing quality. Products included pure resveratrol capsules or multi-ingredient formulations with standardized amounts of resveratrol and other phytochemicals. Samples were analyzed for total trans-resveratrol, flavonoids, procyanidin, polyphenol content and the results were compared with the content declared on-label. Only five out of 14 brands had near label values, compliant with Good Manufacturing Practices (GMP) requirements (95-105% content of active constituent), four products were slightly out of this range (83-111%) and three were in the 8-64% range. Two samples were below the limit of detection. The greater the difference between actual and labeledresveratrol content, the lower was the antioxidant and antiproliferative activity strength. Dietary supplements containing pure trans-resveratrolexhibited a greater induction of differentiation towards human leukemic K562 cells when compared to multicomponent products. Great differences currently exist among resveratrol food supplements commercially available and GMP-grade quality should not be taken for granted. On the other side, dosages suggested by most “pure”, “high-dosage” supplements may allow a supplementation level adequate to obtain some of the purported health benefits.  PMID: 23090020