Mercury Exposure More Likely from Fish than Fillings

Q:  Recently a friend alarmed me by discussing the dangers of toxins such as mercury. She was researching possible causes of cancer in a family member and found that some vaccines and dental fillings contain mercury.

Should my daughter with asthma get an influenza vaccine if it has mercury in it?

Should I be worried about the silver fillings in my mouth?

A:  Mercury is a toxin that can cause nervous system problems and kidney failure. In fact, the idea of the "Mad Hatter" originates from the large number of 19th-century hat industry workers who suffered lack of coordination, memory loss and anxiety as a result of their professional exposure. At the time, mercury was used to process hat felt, and the workers inhaled a great deal of it.

Nowadays, our greatest risk of exposure to mercury is with the consumption of specific marine fish such as shark, swordfish and tuna and some fish taken from polluted fresh waters (pike, walleye and bass).

Mercury probably isn't an important cause of cancer. The US Environmental Protection Agency lists mercury as a "possible" carcinogen but has no hard-and-fast proof. Some jobs still have limited exposure to mercury, and care should be taken in the event of a broken glass thermometer containing mercury (call the Poison Center to aid in cleanup).

Silver dental fillings do contain very small amounts of inorganic mercury, which is not easily absorbed by the human body. According to Anthony Ziebert, a professor of dentistry and chairman of restorative dentistry at Marquette University, amalgam fillings are the No. 1 restorative material for the treatment of cavities, and all clinical studies have found these fillings to be safe. He notes that millions of people have benefited from this treatment, and if any risk exists, it is surely infinitesimal. Removing amalgam fillings already in place increase your risk of mercury exposure because of the disruption.

Some vaccines contain mercury in the form of the preservative thimerosal. Most vaccines routinely given to infants and children now do not contain thimerosal, and even a limited number of thimerosal-free influenza vaccines have been made available.

Overall, there is little convincing evidence that thimerosal causes any harm, and guidelines published by the Food and Drug Administration, the Centers for Disease Control and Prevention and the American Academy of Pediatrics suggest that the benefits of influenza vaccine in susceptible individuals (such as pregnant women and people with asthma) outweigh any possible risks. At the same time, these groups recommend that the thimerosal levels in vaccines should be reduced or eliminated as a precautionary measure, and vaccine manufacturers are responding to this plea.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices internal medicine at the Froedtert & Medical College General Internal Medicine Clinic - East. Her column also appears in the Milwaukee Journal-Sentinel.