Perlmutter, medical director of the Perlmutter Health Center in Naples, and author of "The Better Brain Book" (Riverhead, 2004), said most people don't even think of mercury when they see health problems.
"Most of the people we end up treating are those in whom the idea of mercury hasn't been explored," he said. He diagnoses his patients by, first, blood test, and then confirms it by giving them a chelating agent and testing their urine.
"Usually if people had issues relating to mercury, they improve right away," he said. "Generally, people in their 20s and 30s have wonderful recovery, and we see it every day."
Even though mercury-based tooth fillings and vapors from industrial pollution can be culprits for mercury toxicity, Perlmutter said most of his patients get it from fish.
"I think more and more it's from fish, because the levels are getting higher and higher, and dentists are using less and less mercury -- not because they're concerned about the mercury (although they should be), but because aesthetically people prefer white fillings," Perlmutter said.
He still thinks people should eat fish "but much less than they do." He recommended people eat fish that are low in mercury, such as tilapia and wild salmon, about twice a month.
Women in their childbearing years, he added, shouldn't eat any fish.
But Philip W. Davidson, who has spent 15 years studying children in the Seychelles born to mothers who consume high amounts of fish, hasn't seen any adverse effects, and thinks people shouldn't be so quick to cut fish from their diet.
Davidson, a professor of pediatrics at the University of Rochester, said he thinks there is not enough evidence for Americans to be cutting fish entirely out of their diet based on mercury fears.
"Our own feeling is that warning people not to eat fish has adverse effects of its own because fish is very nutritious," he said.
Davidson has been working on a study conducted by the University of Rochester Medical Center that suggests eating fish -- and therefore consuming mercury -- during childbearing years and pregnancy may not be problematic after all. In 1990, Davidson along with other researchers began studying children in the Seychelles, an archipelago nation off Africa's eastern coast, where women typically eat 12 meals of fish per week -- even when they're pregnant.
"The hypotheisis has always been that there are adverse effects from consuming fish during pregnancy," Davidson said.
The mothers -- who predominantly eat karang or jack but also regularly consume tuna, red snapper, parrotfish, mackerel, kordonye and grouper -- have mercury levels far higher than the average American. The Seychelles women in the study averaged six parts per million, while the average American has one part per million.
The researchers have measured the functioning of 700 children based on 64 different "endpoints," including cognitive abilities, perception, social skills and memory. The oldest children in the study are 15, as they were born when the study began.
"Up to now, six times we've seen these kids, and we've been unable to confirm adverse effects," Davidson said.
The study recently received funding to visit the Seychelles and measure the children twice more.
Perlmutter cautions against people thinking they are safe to eat all the fish they want based on this study.