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In 2009, a hyper-specialized biomedical journal called NeuroToxicology published a fascinating piece of poison sleuthing (http://www.ncbi.nlm.nih.gov/pubmed/19732792). The article documented a disturbing series of 11 cases all of whom shared an unusual and crippling constellation of troubles comprised of profound impairment of the nervous system and an inability to produce an adequate number of blood cells. The specific neurological problems included damage to peripheral nerves (called neuropathy) and the nervous system of the spinal column (called myelopathy). Four of the eleven were wheelchair-bound and four others required a walker for assistance. Moreover, these were not cases selected from an elderly, infirmed population: on average they were 46 years-old at symptom onset (the youngest was 31).
The treating physicians solved part of the puzzle early on. They established that a rare but recognized cause of combined cause of nervous system damage and bone marrow damage was at work - copper deficiency. Copper is an essential nutrient metal. We all need to take in certain amount of copper in our diets. Evolution has allowed for this to be tightly regulated in order to protect us from too much copper getting into our bodies. In fact, a failure of this system is manifest in a serious genetic illness of copper overload (Wilson's disease). In contrast, too little copper is a hard achieve, although sometimes it is seen after gastric surgery or prolonged intravenous nutrition insufficient in copper.
There is one other well appreciated cause of copper deficiency: chronic excess intake of zinc, a practice that interferes with normal copper absorption. This problem is linked to the overuse of zinc-containing dietary supplements. A rare source of exogenous zinc is the pathological ingestion of coins associated with severe psychiatric illness; this has emerged as a particular problem following the substitution of zinc for copper as the major metal constituent of the U.S. penny. Early on for these 11 cases, the treating physicians not only documented the presence copper deficiency, but also showed that there was concomitant excess zinc. Then they hit a roadblock. Each of the patients denied knowingly ingesting heavy amounts of excess zinc; mysteriously, supplementation with copper corrected the blood deficiency yet elevated zinc levels persisted.
Then, in 2008, a scientific report appeared linking elevated zinc levels to the use of denture adhesive. Zinc is a common additive to such products. The eleven patients, whose source of illness until then had remained obscure, were re-contacted. Each and every one reported that indeed they had used denture adhesive for a number of years. Furthermore, all of them also shared a common complaint - ill-fitting dentures that led them to apply relatively large amounts of these over-the-counter zinc-containing products. Seven had used a Poligrip product alone; one, Fixident; and three, both. Unfortunately, even with cessation of use there was only modest improvement overall (one patient advanced from a wheelchair to a walker and one gave up his cane).
Although the case series first became available online in September 2009, it was not until mid-February 2010 that GlaxoSmithKline (GSK, the parent company of the Poligrip product line) announced that it was ceasing to make or market zinc-containing Super Poligrip, although it did not recall product already on the shelves. In a carefully-worded "consumer alert," it acknowledged that "...recent publications suggest that an excessive intake of zinc-containing denture adhesives over several years may lead to the development of neurological symptoms...." (www.mypolicare.com).
GSK may have interpreted the convincing cause and effect relationship meticulously documented in Neurotoxicology as a mere suggestion, but they at least went farther than their competitor, whose web site insists, "The amount of zinc an average denture adhesive user would ingest from daily usage of Fixodent is: Less than the amount of zinc in most daily multivitamins; Less than 6 oysters (fried or raw); Comparable to 6 oz ground beef. " (www.dentureliving.com). So far the US Food and Drug Administration, which belatedly acted last summer to protect the public from zinc-containing nasal sprays, has taken no action on denture adhesives.
Advertisements reassure dental wearers to bite down hard without worrying. If they are eating their apples with a chaser of zinc, it may not be enough to keep the doctor away.
