Denture Cream Zinc Poisoning Study Reviewer Failed to Disclose Conflict

Did a consultant for Proctor & Gamble, the maker of <"">Fixodent denture cream, help suppress an important study that showed a link between zinc-containing denture adhesives like Fixodent and severe nerve damage? The study, though completed in 2006, wasn’t published in the journal “Neurology” until 2008. According to a recent ABC News report, the denture cream zinc poisoning study was delayed because of criticism from its peer reviewers, including Dr. Kenneth Shay, a Michigan dentist.

At the time, Dr. Shay did not disclose his conflict-of-interest as a consultant to Proctor & Gamble. ABC News also reported that in addition to criticizing the study, Dr. Shay also sent draft reports of the study to Procter & Gamble, Good Morning America reported. In one e-mail, he said, “Please be circumspect because, as a reviewer, I’m not supposed to be passing an unpublished manuscript around.” It’s not clear what Procter & Gamble did with the information, ABC News said.

But now, the lead author of the “Neurology” study is defending its peer review process, and denying that Dr. Shay caused it to be delayed or watered down. Sharon Nations, MD, associate professor of neurology at the University of Texas Southwestern Medical Center in Dallas, told MedScape today that the suggestions made by the study’s three-member review panel helped to improve the study.

For his part, Dr. Shay acknowledged to MedScape that he was wrong not to disclose his connection with Proctor & Gamble when he reviewed the denture cream zinc poisoning study, but claims that was only because he thought the company had actually referred him to “Neurology.” He also said sending the study to someone Proctor & Gamble to “double-check” his facts was a mistake. However, Dr. Shay insists his review was fair and unbiased.

In a statement, Robert A. Gross, MD, PhD, the editor-in-chief of Neurology, condemned Dr. Shay’s behavior.

“Dr. Shay did not disclose any conflict of interest to the editor-in-chief of Neurology, he writes.”Furthermore, it appears that Dr. Shay improperly shared the manuscript authored by Dr. Sharon Nations to Procter and Gamble, in violation of the journal’s confidentiality policy.”

“Neurology considers violations of our ethics policies to be egregious misconduct, and the academy’s general counsel is reviewing its options with the editors,” Dr. Gross adds. “Furthermore, we will continue our ongoing review of policies for authors and reviewers to ensure that the integrity of Neurology is preserved for our readers and the patients and caregivers affected by the research we publish.”

The “Neurology” article reported on four patients – all of whom used excessive amounts of zinc-containing denture cream – suffering from neuropathy and other neurological symptoms typical of zinc poisoning and copper depletion. The study concluded that excess use of zinc-containing denture cream could have been responsible for their symptoms.

The human body does need zinc – but only in small amounts. Studies show that consuming at least 50 milligrams of zinc a day for a few months could lead to copper deficiency, which can cause anemia, bone loss, nerve damage and other problems. Ingesting 80 or 100 milligrams or more for months or even years can lead to irreversible damage.

As we’ve reported previously, in March 2010, Procter & Gamble began cautioning consumers about zinc in Fixodent denture creams on it website, The new information stated that some reports suggest that excessive and prolonged zinc intake may be linked to adverse health effects. At the same time, Procter & Gamble also began shipping Fixodent with updated label instructions on how to apply the product. The zinc, however, remains in Fixodent.

Proctor & Gamble didn’t go nearly as far as GlaxoSmithKline, maker of <"">Super Poligrip products which also contained zinc. A month prior to the release of the Fixodent zinc caution, Glaxo announced it would stop the manufacture, distribution and advertising of three Super Poligrip products that contained zinc. In a statement posted on its website, Glaxo said it was reformulating the Super Poligrip products as a precautionary measure to minimize any potential risks to consumers.

Both Proctor & Gamble and Glaxo have been named in <"">denture cream lawsuits alleging that excessive exposure to zinc in Fixodent and Super Poligrip caused severe nerve damage.

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