Your health this month.

Health and medicine explained.
July 1 2005 3:39 PM

Your Health This Month

Mercury in vaccines and dental fillings, avian flu, episiotomies, and more.

Mercury in Vaccines: Why you can stop worrying about thimerosal.

State of the Science: The claim that a spate of autism has been caused by the past presence of mercury in vaccines, through the preservative thimerosal, is affecting public-health policy. Even though there is strong evidence to refute the thimerosal-autism connection and even though—let me hasten to reassure you—the mercury is now gone, families in my pediatric practice continue to be afraid to immunize their children. Thimerosal came to be incorporated into vaccines nearly 80 years ago for a good reason. Is there cause today to think that the mercury-containing preservative is or was unsafe?

Prognosis: No. Different forms of mercury are associated with different levels of toxicity. Methyl mercury, an organic compound whose molecules directly and easily penetrate the nervous system, causes extremely serious environmental damage and poses a major health risk, especially to pregnant women and children. But neither thimerosal nor ethyl mercury, the compound into which the body breaks it down, cross the blood-brain barrier and enter the nervous system. Both are eliminated from the body quite rapidly and do not accumulate between vaccine doses. In the tiny amounts formerly associated with vaccines, there is no sign that either is toxic.

Fall-out: Mercury was eliminated from vaccines in 1999 out of concern that the thimerosal panic would lead to widespread refusal of vaccines. That decision was prudent, if only to preserve faith in immunization, but it was also costly. Since a Royal Commission in Australia investigated a vaccine disaster there in 1928 (go read about the history, really!), it has been clearly established that vaccines packaged in multidose containers must contain a preservative. The alternative is to bottle vaccines in tiny single-dose containers, taking meticulous care to ensure that the vaccine is not contaminated in the manufacturing or bottling process. This method has greatly increased costs and led to vaccine shortages in the past few years. As public funding for children's health and access to medical insurance drops, many poor children may be priced out of the market for vaccines. That would reduce the average rate of immunization—and raise the rate of illness.

Mercury in Teeth: It's safe for dentists to use, too.

State of the Science: The legislators of my home state of Connecticut have shown a remarkable ability to enact well-intended but wrong-headed laws governing medical practice, and they might be about to do it again. At issue is another use of mercury, this time in dental fillings. Dentists have been using mercury-containing amalgam (called dental amalgam) to fill cavities in teeth since the early 19th century. This material is easy to use, durable, and relatively inexpensive. But questions about the harmful effects of dental amalgam have led to proposals either to outlaw it outright or to forbid it by extending Connecticut's existing "zero-mercury" statute. Maine and New Hampshire already have laws requiring dentists to inform their patients about dental amalgam's mercury content. How much risk, to the patient or to the environment, does the amalgam pose?

Prognosis: Very little, if any. The environmental risk is virtually eliminated by a device called an amalgam separator that dentists use to prevent the material from entering the environment via the sewage stream. (The amalgam is recovered and reprocessed.) The risk to patients with amalgam fillings is similarly low: A recent study of more than 1,500 veterans detected no evidence of neurological harm related to the fillings, confirming the results of several previous studies.

So, how to explain the frenzy over amalgam fillings? Like thimerosal, dental amalgam is prey to risk confusion. The clear environmental harm caused by dumping large amounts of mercury or its compounds makes it harder to accept that tiny individual exposure to metallic mercury probably doesn't matter much. A few dentists have exploited the confusion to promote the lucrative practice of removing old amalgam fillings and replacing them with mercury-free materials. Law firms interested in setting the stage for class-action suits have also stoked fears.

Contrarian thought: Conspiracy theorist that I am, I wonder if the agitation over minor mercury sources obscures the real cause of mercury contamination of our seafood and water: coal-fired power, ore processing, and garbage incineration. U.S. power plants dump almost 50 tons of mercury a year into the air, and other industrial sources contribute another 100 tons annually. The Environmental Protection Agency recently gave the power plants a free pass until 2018, at which time they must reduce the 50 tons they currently emit to 15. Are the trivial and demonstratively non-harmful uses of mercury by dentists—or, in the past, to protect vaccines from contaminants—distracting us from the serious environment-poisoning?

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