Zinc Poisoning Linked to Popular Denture Creams
Reports Suggest Overuse of Fixodent and Older Version of Poligrip May Cause Nerve Damage
Feb. 15, 2011 -- Many cases of mysterious nerve damage turn out to be caused by overuse of popular denture products, an increasing number of reports suggests.
The culprit: zinc in Fixodent, from Procter & Gamble, and -- until it became zinc-free last May -- Poligrip from GlaxoSmithKline.
The body needs zinc. But because the body balances zinc and copper, people who get way too much zinc have dangerously low levels of copper. Moreover, zinc overdose itself may be toxic.
The result is bone marrow suppression and degeneration of the spinal cord, usually resulting in crippling nerve damage. It's been called "human swayback disease."
Some patients have ended up in wheelchairs. At least one patient died. Lawsuits have blossomed, with a bellwether case scheduled to be heard this summer in Miami. GlaxoSmithKline already has settled a large number of cases; Procter & Gamble has not.
For years, doctors have reported mysterious cases of people suffering a spastic gait, limb weakness and numbness, and difficulty walking. Only around the year 2000 did researchers find that these patients have very low levels of copper in the blood. Copper deficiency can be caused by an overdose of zinc, but most of these patients had no obvious exposure to zinc.
In 2007, Italian researcher Marco Spinazzi, MD, suggested a link to denture cream. And in 2008, Sharon Nations, MD, and colleagues at the University of Texas Southwestern Medical Center identified four patients for whom this was their main source of zinc.
Since then, other researchers have reported similar findings. Of special note: the death of a Georgia patient from zinc overdose linked to denture cream.
Vanderbilt researcher Peter Hedera, MD, had long wondered about unexplained cases of low blood-copper levels in which patients developed crippling disabilities. After hearing of the Nations study, he investigated 11 of these patients. Sure enough, all 11 were using excessive amounts of denture cream.
"Poorly fitting dentures requiring large amounts of denture cream to provide a sufficient seal appear to be the common characteristics of patients," Hedera and colleagues reported in the journal Neurotoxicology.
Linking Zinc Poisoning to Denture Cream
Why did it take researchers so long to figure this out? In an explosive report, ABC news recently reported that publication of the Nations study in the journal Neurology was delayed by a reviewer, Kenneth Shay, DDS, with undisclosed financial ties to Procter & Gamble. Shay, it turned out, violated his confidentiality agreement by sharing the unpublished manuscript with P&G.
"The American Academy of Neurology considers any violation of these ethics policies to be egregious misconduct," the organization says in a statement provided to WebMD.
Shay says he was critical of the Nations report because he felt the researchers' method of measuring zinc in dental cream had "fundamental flaws." After the Nations team refused to accept his revisions, he says, he sent the manuscript to P&G.