In recent years, numerous misperceptions have circulated surrounding mercury and canned tuna. In many cases, the facts don't support the rumors. Here are some common myths, and what nutritionists and scientists are really saying.
Myth #1
Many babies are born in the U.S. with mercury levels in their blood that may put them at risk for neurological problems.
This myth has been widely circulated by environmental groups pressing for stringent mercury emission standards for coal-burning power plants. To further their political goals, these groups erroneously state that roughly one in six babies born in America - or 630,000 infants born each year - has a blood mercury level above the monitoring level set by the Environmental Protection Agency (EPA).
Here is what is actually true. What the environmentalists cite as the cutoff level for safety is what is called the "reference dose," which is used by EPA to monitor mercury concentrations in the environment. In determining this reference dose, EPA conducted a major study to find the lowest mercury levels in the blood of pregnant mothers that could have a neurological impact on children. This is known as the "risk level," even though it is not know what effect, if any, this subtle variation may have in the real world. As a next step, EPA divided this number by 10 - arriving at a ten-fold safety factor, which the government applies in regulating mercury levels in fish. The resulting reference dose set by he EPA for mercury levels in fish is the most stringent in the world. Therefore, if women have this very low level of mercury in their blood, they actually have an amount that is ten times lower than the true risk level.
To come up with their alarming estimates of the number of children at risk, environmentalists used a major study conducted in 1999 by the Centers for Disease Control and Prevention (CDC), which analyzed mercury levels in the blood of a random sample of American women and children. This study found that not a single woman or child in the United States was even close to the risk level. But because this study found that 8 percent of the women surveyed had mercury levels slightly above EPA's reference dose, the environmentalists multiplied this number by the total number of births in the U.S., arriving at 300,000 babies.
And since that number didn't seem big enough, the environmentalists went one step further - by stating that babies have even more mercury in their blood than their mothers do (which is true but was factored into the original calculation of the "reference dose" used by the EPA). Based on this doubling up of the numbers, the environmentalists were able to bump up their estimates to 630,000 babies. But this analysis completely misrepresents what EPA's reference dose means, as well as the fact that EPA builds in ten levels of safety.
In reality, no government study has ever found unsafe levels of mercury in women or children who eat canned tuna. This includes the 1999 CDC study, which has been recently misrepresented by the environmentalists. This study found that every one of the women and children studied - 100 percent - had mercury levels that were significantly below the threshold for any known risk.
Moreover, a follow-up CDC study in 2004 found that mercury concentrations in the blood of American women have actually declined over a four-year period (1999-2002). While CDC estimated that 8 percent of U.S. women had mercury levels at or slightly above EPA's reference dose in 1999, this number has dropped to only 6 percent. For this reason, the Food and Drug Administration (FDA) and EPA are telling pregnant and nursing women: "With a few simple adjustments, you can continue to enjoy [fish including canned tuna] in a manner that is healthy and beneficial."
Myth #2
It is possible to get poisoned from the mercury levels in fish.
No single person in this country has ever experienced mercury poisoning from eating fish. And the same is true for most countries around the world.
There have been four cases worldwide where people have been poisoned by consuming foods containing very high concentrations of methylmercury. During the 1950s, 111 people from Minamata City, Japan died or experienced neurological disorders from eating fish contaminated with very high concentrations of methylmercury - up to 40 parts per million, compared to the FDA limit of 1 ppm. In this case, an industrial facility was releasing manufactured methylmercury directly into Minamata Bay. A second incidence in 1965 occurred in Niigata, Japan where 120 people were similarly poisoned.
Another two incidents involved people in Iraq who ate bread from grain that was contaminated with a fungicide containing mercury. Here, the people were exposed to even higher levels of mercury than in Japan and thousands were hospitalized.
In the more than 30 years since the Iraqi poisonings, the University of Rochester in New York is closely followed populations eating large amounts of fish, including Samoans, Peruvians, and residents of the Seychelles Islands. The researchers have not found any adverse effects from mercury in either adults or children among these substantial fish-eating peoples.
Myth #3
The amount of mercury in fish can cause serious neurological harm to unborn children.
This frequent claim is based on unconfirmed and unresolved evidence from a study conducted in Faroe Islands, located in the North Sea between Scotland and Iceland. People in the Faroes regularly consume ten times the amount of seafood that most Americans eat, including a large amount of whale meat. When the children in this study were given 17 neuropsychological tests, some scored slightly below average on three. Scientists have since disputed whether there was ever a statistical correlation. They further note that, even if there was a correlation, it's impossible to know if it was caused by mercury, as the mothers were also consuming high levels of other toxins such as PCBs and DDT.
Also disputing this claim is the conclusion of another major study conducted by a team of University of Rochester researchers who investigated 779 mother-infant pairs in the Seychelles Islands off the coast of Madagascar. The results of this study, which followed children from before birth in 1989 to 9 years of age, were published in the medical journal The Lancet and found no detectable risk from the low levels of mercury exposure to these children - despite the fact that their mothers eat 10 times as much seafood as people in the U.S. and have an average of six times as much mercury in their bodies. In fact, the children in this study have been tested five times, and each time no harmful effects from mercury have been found.
Myth #4
The government is warning pregnant and nursing women not to eat canned tuna, and especially albacore.
This is absolutely not true. To ensure that pregnant and nursing women have the best advice about how to add fish to their diets, the FDA and EPA issued a joint advisory on March 19, 2004 that states "women and young children in particular should include fish and shellfish in their diets due to the many nutritional benefits."
To help pregnant women and moms choose fish that are low in mercury, FDA and EPA have identified 5 commonly eaten fish with very low mercury levels: shrimp, salmon, pollock, catfish and canned light tuna. The FDA and EPA further advise pregnant and nursing women they can safely eat up to 12 ounces a week of these fish. The average serving size of canned tuna is 2 ounces, which gives pregnant and nursing woman many options to continue eating canned tuna.
The government advisory also tells pregnant and nursing women that they can safely eat up to 6 ounces a week of canned albacore tuna. In general, there are 2 ounces of albacore in a typical serving.
However, the advisory also identifies those types of fish that have higher levels of mercury and should be avoided by pregnant and nursing women, and young children. These fish are shark, swordfish, tilefish and king mackerel.
Myth #5
Government studies find high levels of mercury in canned albacore tuna.
No, they don't. When FDA conducted a survey of canned tuna samples, the agency found that canned albacore tuna contains somewhat more mercury than canned light tuna. But the average amount (0.35 parts per million or ppm) is still exceedingly low. To put this amount into perspective, FDA has set a limit of 1.00 ppm for mercury in fish - and both canned light and albacore tuna are well below this level.
Myth #6
The amount of mercury in canned tuna is increasing.
Absolutely not. Studies find that the amount of mercury in canned tuna has not increased in the last 25 years. In fact, a major study measured mercury concentrations in Yellowfin tuna caught off the coast of Hawaii in 1998 and compared them to similar measures of Yellowfin tuna caught in the same area in 1971. That study found no increase in mercury levels.
Myth #7
To be on the safe side, women should avoid eating fish when they are pregnant or nursing.
This myth does a terrible disservice to women, who need increased amounts of the omega-3 fatty acids found in canned tuna and other types of fish during pregnancy. For example, canned tuna contains DHA (docosahexaenoic acid), an omega-3 fatty acid that is essential for the healthy development of the fetus and young child. According to scientific studies, DHA comprises approximately 40 percent of the polyunsaturated fatty acid content in the cell membranes in the brain and 60 percent of the cell membranes in the retina. DHA is transferred from mother to the fetus at a high rate during the last trimester of pregnancy.
It is because fish is so important to a pregnant and nursing woman's diet that FDA and EPA issued their seafood advisory - which tells these women how to receive the benefits of fish while reducing their exposure to mercury levels. According to the government advisory: "Fish and shellfish are an important part of a healthy diet... So, women and young children in particular should include fish or shellfish in their diets due to the many nutritional benefits."
Revised: August 2005
