CBS5 - Canned tuna is a healthy source of vitamins and protein, but it also contains some levels of mercury. Whether it's enough to require posted warning signs is being debated in a state appellate court. In the meantime, CBS 5's Sue Kwon conducted her own unscientific experiment tracking consumption of canned tuna and measuring levels of mercury.
The experiment involved eating 20 five-ounce cans of albacore tuna over 20 days and not eating seafood that could contain mercury and impact the experiment.
Canned tuna is packed with lean protein and omega-3 fatty acids which studies show benefit the heart, brain, and eyes.
But even the fishing industry acknowledges, it does contain mercury. It's a chemical that could be toxic at certain levels and erase those benefits as well as cause problems in an unborn baby.
California's Proposition 65 requires warning signs to be posted at the fish counter. The law is intended to protect California citizens from chemicals known to cause cancer or other reproductive harm. Canned tuna companies won a legal fight to be exempt from the law, but now the California Attorney General's office is appealing that court decision.
"We know that methyl mercury is a potent neurotoxin that can harm the unborn baby," said California Deputy Attorney General Susan Fiering. "In Minamata Bay, (poisoning of the 1930s-1960s) mercury caused children to be born with cerebral palsy, with small brains, and undersize brains."
Forrest Hainline who represents the three biggest canners, (Bumblebee, Chicken of the Sea, and Starkist,) said warnings in supermarket aisles would decrease fish consumption and have a negative impact on public health.
"It would be completely conflicting with federal law which wants women to understand that while they are pregnant or may become pregnant, eating fish is good for them and their unborn children," Hainline said.
The problem is doctors really don't know how much tuna it takes for a person to accumulate higher levels of mercury.
While the test sounds risky, she was not pregnant or about to become pregnant and was not expected to hit levels associated with side effects.
After eating 20 cans, a phone call comes from the doctor. Dr. Jane Hightower said, "I want you to stop your experiment. It's not worth the risk."
Dr. Hightower is an expert in mercury poisoning and a known critic of the fishing industry. She is not happy with the National Fisheries Institute website which said canned tuna is "healthy" for pregnant women and they can safely eat 6-ounces or a little over a can a week.
She tells pregnant patients, "Why eat mercury at all when you don't have to? Canned albacore tuna has an average of .35 parts per million and they say tuna is a low mercury fish."
It can be considered "low" if one compares it to the legal mercury limit of 1 part per million set by the Food and Drug Administration. But, the allowed level of mercury in the U.S. is double that of Canada (.5ppm), Europe (.5ppm), and Japan (.4ppm). So elsewhere, canned tuna would not be considered a "low" mercury fish.
The experiment illustrates that even at levels below the federal limit, mercury accumulates in the body reaching what Dr. Hightower and an independent lab flagged as "high" levels in a short period.
At the start of the experiment, Sue Kwon's blood mercury level was low at 4 micrograms per liter. In 10 days, it went to 8.9 micrograms per liter. Then in 10 more days, it climbed to 17.2 micrograms per liter. By day 20, it had quadrupled. "Anytime in a woman's body she reaches a 14 or 15 she stands a chance of knocking IQ points off her child's brain," Hightower said.
If the experiment continued, Dr. Hightower said the mercury would accumulate mercury faster and the level would spike. Hightower said, "You probably would've doubled again in another 10 days and then probably leveled out at in a steady state somewhere in the 50 range."
Hightower's patients with blood mercury levels that high have experienced these symptoms. "They get body aches, joint pain, muscle aches, head ache, trouble sleeping, troubles with thinking and memory, stomach upset," she said.
The canned tuna industry said there are no scientific studies proving a link between mercury levels in fish and specific health effects.
"These are issues that need to be discussed with a doctor not the grocery store checkout clerk or the Safeway manager. It's that simple," Hainline said.
Fiering believes consumers need in-store education materials. "There are a lot of women out there who don't use computers and don't see their doctors regularly and are not getting regular checkups and they're not getting the information they need," she said.
According to the Department of Public Health, 17 micrograms per liter is higher than the average exposure which is about 6 micrograms per liter. The fishing industry recommends eating 2-3 servings of seafood a week including canned tuna. A "serving" of canned tuna is half a can, about enough to top 3 crackers. Obviously, the experiment involved eating more than what's recommended.
Even so, at 17.2 micrograms per liter, Sue Kwon did not feel side effects. But, she is lowering her mercury level by avoiding tuna and sweating it out at the gym. She is continuing to eat fish as recommended for nutrients and health benefits. But, she is making sure to mix the varieties and eating tuna along with fish that do not contain as much mercury.