Zinc Levels In Poligrip Scrutinized

Until very recently, the denture adhesive Super Poligrip contained high levels of zinc — enough, scientists say, to cause neurological damage in people who used too much of it. Host Linda Wertheimer talks to New York Times columnist David Leonhardt about why the product remained on the shelves for so long.

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LINDA WERTHEIMER, host:

For decades, people who wear dentures have turned to products like this one:

(Soundbite of advertisement)

Unidentified Woman: At last, I'm eating a carrot. Thanks to Super Poligrip with its new, ultra-hold formula.

WERTHEIMER: GlaxoSmithKline, the company that makes Super Poligrip, recently decided to change that formula after a number of Poligrip customers filed lawsuits against the company. They allege that using Super Poligrip led to neurological disorders.

Columnist David Leonhardt wrote about this recently for the New York Times. Welcome to the program.

Mr. DAVID LEONHARDT (Columnist, New York Times): Thank you, thanks for having me.

WERTHEIMER: Could you just explain to us why this product is connected to nerve damage?

Mr. LEONHARDT: Absolutely. So these products contain zinc. Super Poligrip contains zinc, which helps with adhesion. It helps the dentures stick. Zinc is one of those substance that the human body needs but only in small amounts.

When you get too much zinc, it can lead your body to have a copper deficiency, and that, in turn, can lead to neurological damage, and that seems to be what has happened here. Customers who have used significant amounts of this cream have developed really severe neurological problems. In one case, there appears to be a death that was tied to use of these creams.

WERTHEIMER: Now, the folks who are suing the companies that produce denture adhesives containing zinc, wouldn't it be fair to say that very likely, most of them are older? Is it clear that denture adhesive is the main cause of their infirmities, of their nerve damage?

Mr. LEONHARDT: It is not 100 percent clear because there's almost always some uncertainty in science, but it seems highly probable. There was a recent study conducted by a scientist at Vanderbilt University in which he went out and found 11 people with very elevated levels of zinc.

He didn't know why they had the levels, and then he tested them. It turned out all 11 of them had elevated levels of zinc because they were using large amounts of this denture cream. He told me that really surprised him. He didn't expect to see all 11, but it seems to be one of the main causes of people having too much zinc in their system.

WERTHEIMER: Is this a question of misusing the product, of slathering on the adhesive?

Mr. LEONHARDT: Well, that's really where we get to the debate. The companies say that this is a matter of misusing the product, and the people who have used it and use too much, according to the companies, and gotten nerve damage say no, that it's a matter of there not being clear enough directions.

And there were not very explicit directions on these products about how much to use even when evidence began to emerge very clearly that these creams were causing the problem, and that really started in 2008.

The companies really didn't respond very aggressively. I mean, what GlaxoSmithKline did was they put a note in the creams that said: For best results, start with a small amount. That's not exactly a really clear warning.

WERTHEIMER: So David Leonhardt, here's what I don't understand. This is an old product. I mean, I can remember those these commercials about sticking your dentures down going on for years. How come it's just now becoming an issue?

Mr. LEONHARDT: Well, zinc began to be used in denture cream in 1996, in Poligrip. So it's been in this denture cream for 14 years. This is a period in which the science has been evolving. We knew for a long time, back to the 1950s, that zinc could cause some problems, but we really didn't know until earlier this decade about this two-step link: zinc to copper deficiency, copper deficiency to nerve damage. And then it was in 2008 that you got the first study that tied the denture cream to these problems.

Now, I don't think we should have needed all this science to tell us that a product with very high levels of zinc, which this cream had, would likely have caused these series of problems because much of the science was there, but the companies didn't take particularly strong action, and they relied on consumers to get it right. Most did, but some significant number appeared not to have gotten it right. And it does make you wonder more broadly whether we are taking these sorts of toxic risks seriously enough and whether we have strong enough regulatory oversight of companies because this is just one example - lead in paint, mercury in tuna, now zinc in denture cream in which companies have not been all that aggressive about protecting consumer safety.

WERTHEIMER: David Leonhardt is a columnist for the New York Times. Thank you very much for joining us.

Mr. LEONHARDT: Thank you.

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