‘Buyer beware’: Resveratrol supplements fail NOW testing

“‘Buyer beware’ certainly applies to resveratrol, as we found significant problems with most products tested,” said Dan Richard, vice president of global sales and marketing at NOW. “Once again, NOW will share this info with Amazon directly and with the FDA, in hopes of further action.”

This is the company’s 18th round of product policing​ since it initiated its testing program in 2017 to evaluate lesser-known brands sold online. All rounds to date have raised concerns tied to issues such as potency, labeling, contamination, adulteration and heavy metals across product categories.

Resveratrol in the market ​

First isolated in 1939, resveratrol is a polyphenol naturally found in grapes, red wine, peanuts and herbs, and it performs largely as supplement across antioxidant, beauty, reproductive, heart and circulation, and cognitive health subcategories. 

According to data from market research firm SPINS for the 52 weeks ending July 17, 2024, U.S. sales totaled over $5.1 million, up from close to $4.7 million a year prior—with antioxidant supplements leading the way at over $4.8 million.

“Overall, the category is seeing impressive growth this year with a 9.4% increase in sales compared to a year ago,” said a spokesperson for SPINS. “When broken down into subcategories, beauty supplements and condition specific supplements are the largest areas of growth for resveratrol.” 

Regarding quality, NOW explained that the two types—cis-resveratrol and trans-resveratrol—have the same molecular formula, but trans-resveratrol is more bioavailable and easier for the body to absorb. The most common source in dietary supplements is Japanese knotweed, with the trans-resveratrol portion often testing between 50% and 98%.

“Natural resveratrol also contains many trace levels of additional antioxidants, while synthesized resveratrol is isolated chemically and does not contain other synergistic components,” the company added.

The test results​

For this round of in-house testing, NOW purchased two bottles of each of the 30 resveratrol brands on Amazon in June. It also sent one unopened bottle of each product to independent contract laboratory Alkemist Labs. Both labs used high-performance liquid chromatography (HPLC) with ultraviolet light detection (HPLC-UV) as correct testing method to measure the amount of trans-resveratrol in each sample. 

Of the 30 brands tested, NOW reported that two-thirds had “confusing or dishonest labeling” for resveratrol, 21 tested below labeled potency and 17 contained less than 10% of claimed potency. 

NOW also analyzed its own brand, which it has sold since 2015, and found that it met an average 114% of label claim, making it one of four products tested designated as having “honest labeling”.

“Many brands display the highest potency number on the front panel and in Amazon search terms, but ‘tricky’ labeling on the side panel may not match numbers,” the company shared in a statement, noting that resveratrol is a very interesting natural compound to test due to its complexity and labeling options.

Both labs also used high-performance thin-layer chromatography (HPTLC) for internal testing to verify if the resveratrol was extracted from Japanese knotweed. Most of the samples contained resveratrol extract with a purity of over 98%, but in these cases, neither lab could confirm the botanical source. 

“The results above further substantiate the fact that the market is saturated with unscrupulous companies that make false claims,” Richard said. “Consumers should be cautious when buying from lesser-known brands and opt for trusted, honest and transparent brands.”

Commenting on the results, Daniel Fabricant, PhD, president and CEO of the Natural Products Association, noted that some of the same brands continue to fail NOW testing round after round, indicating a potential Current Good Manufacturing Practice (cGMP) issue and suggesting that Amazon and FDA may want to investigate further.

"I think too often we see the narrative of the retailer as the 'quality gatekeeper' or some derivative—it’s important what NOW is doing as it really re-establishes that it’s really about the brand, especially as it pertains to quality," he told NutraIngredients-USA.

"The values of the brand are ultimately where we rise or fall. Brands that aren’t invested in the industry and aren’t working with independent retailers or specialty retailers or don’t engage in the community in other ways have made lots of money from electronic platforms because of the premise of the platform or retailer as the gatekeepers. This is added evidence that brands not being immersed in the community don’t really hold up to scrutiny.”

NutraIngredients-USA reached out to Amazon for comment but did not hear back prior to publication.