Mercury levels in fish eaters

This week the New York Department of Health and Mental Hygiene issued a report on mercury levels in the city's population. Taken from the city's Health and Nutrition Examination Survey (HANES), the report found that "among women 20-49 years old in New York City, the average blood mercury level is 2.64 µg/L (micrograms per liter), three times that of similarly-aged women nationally (0.83 µg/L)," and "approximately one quarter of New York City women in this age group have a blood mercury level at or above 5 µg/L."

Another interesting fact from the HANES study: "Higher-income New Yorkers have higher mercury levels; New Yorkers in the highest income bracket average 3.6 µg/L, compared to 2.4 µg/L among the lowest income group."

We usually think that high-income people are healthier because they have access to better food and better health care. So why do high income New Yorkers have higher mercury levels? Because... they have access to better food. High-income people tend to eat more fish, and more expensive fish (can you say sushi?) and it is this fish that is contributing to higher levels of mercury in these women's blood.

I met Dr. Jane Hightower earlier this year at a conference. In the mid-to-late 1990s, Hightower, a thin, dark-haired woman with the intensity of a bloodhound following a choice scent, had dozens of patients being referred to her who had similar yet indistinct symptoms. Other doctors may have finally given these patients a diagnosis of something—Lyme’s disease, chronic fatique, fibromyalgia—but the patient’s tests didn’t quite fit the normal profile for the diagnosis that they had received; nor had treatment seemed to make them any better. Desperate for help, and often years into their hunt for an answer, they’d show up in Hightower’s office.

“I enjoy problem solving,” Hightower, an internist at San Francisco’s California Pacific Medical Center, explains, “so I get a lot of patients that have been through numerous doctors, and through even more numerous tests. These patients were coming in and saying to me, ‘I just don’t feel well. I have a headache all the time, and always feel like I have a hangover. My stomach’s upset. I have muscle and body and joint pains, and I have trouble thinking.’

These patients were a mixed lot: they spanned all age groups, from young kids to the elderly, included both men and women, and represented various ethnic groups. There were CEOs and physicians, secretaries and soccer moms. Many mentioned loss of motor control, and a number added hair loss to their complaints.

“All these patients had one thing in common—they had a laundry list of non-specific symptoms,” Hightower says.

For a long time, her patients’ symptoms had Hightower stymied, but one day in 1999 one of her colleagues, dermatologist Kathy Fields, mentioned that on a recent trip to Idaho she’d heard a call-in radio program about people with high mercury levels in their hair and blood. The common denominator among the callers was that they fished in Idaho lakes, and ate the fish. One symptom really piqued Fields’ attention: hair loss. Dermatologists frequently deal with hair-loss patients, and Fields knew that at least some of Hightower’s mystery patients reported hair loss.

The two doctors teamed up, arranging to test just one of Hightower’s patients who was suffering from hair loss. “We didn’t even really know what test to ask for,” Hightower says. “But we checked her blood, and it came back with what seemed like a high organic mercury level.”

With the results in hand, Hightower had to figure out what they actually meant. She tried to search the medical literature, but there was a paucity of information on mercury in the common texts that doctors refer to. Next, she checked with the California Department of Health; they said organic mercury could go up to 200 µg/L in blood, so mercury wasn’t the patient’s problem. But Hightower did a little more research, and found that the Environmental Protection Agency put the safe level for blood at less than 5 µg/L. The lab, which typically tested occupational exposures, told Hightower they use 13 µg/L ‘at the end of the work week,’ as the safe figure. Hightower pauses in telling her tale: “I scratched my head, and said, ‘Houston, we have a problem. No one is on the same page.’

Hightower reported the patient’s results to the regional poison control center. They put together a team, and went to the patient’s home and place of business. They searched for a source—and didn’t find one. But they tested all the employees at the business, and found two that also had high levels of mercury. The common denominator seemed to be the same one the Idaho callers had talked about on the radio program: high-mercury results corresponded to frequent fish consumption. Hightower tested a few more patients from the laundry-list group; they too had high levels of mercury.

Knowing that a few of her patients indeed had high mercury—which appeared to be associated with their fish consumption—Hightower decided to look more closely at mercury across the spectrum of patients coming into her practice. She designed an experimental program that involved all 720 patients who came to her office for a one-year period. Each patient was asked to complete a survey that asked questions about fish consumption, vaccination history, and about the number of amalgam, or silver fillings the patient had in their teeth because amalgam is another source of mercury. Her findings: patients who ate a lot of fish had significantly higher mercury levels than patients who consumed little or no fish, frequently exceeding the mercury levels EPA reported to be safe.