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Pregnancy and Fish:
Do We Really Have to Give it Up?
By Courtney Migel
What is the issue?
The demand for knowledge regarding women’s health is increasing. Doctors attempt to stay abreast of cutting edge information and technologies. In turn, they advise their patients as to how they too can remain at the peak of personal wellbeing. However, issues arise that bring with them great amounts of debate and controversy. If one doctor advises you one way, and another doctor says the opposite, which do you believe? Shouldn’t practicing health care professionals be in agreement as to what the most effective treatments really are?
The “Health and Body” column of a recent Glamour Magazine (September 2005) article raised a very pertinent issue: pregnancy and the dangers of eating fish. In the last fifty years this topic has been hotly debated. Some gynecologists are under a different belief system than others regarding research findings, resulting in the confusion of many mothers-to-be. Dating back to the 1920’s and the horrific incident of Minamata, Japan where a village population was exposed to extreme levels of MeHg due to toxic waste, mercury exposure from the consumption of certain types of fish containing high levels of the toxin has become a major public health concern. Yet it wasn’t until the late 1950’s and 1960’s that the breadth of the concern was realized by government agencies and officials and action was taken to protect consumers. In more recent years scientists and researchers have worked diligently to gain a better understanding of how the toxin is passed from the mother to the fetus and the threats that mercury exposure poses to in-utero development. However, all the research has not provided enough concrete data to sustain a single consumer recommendation leaving much room for controversy. Whereas women in one population may be advised to abstain from eating fish, women in other populations may eat upward of twelve servings a week. This paper will attempt to sort out some of the myths and recent research in regards to mercury exposure from seafood and freshwater fish, as well as the effects on mothers and the developing fetus.
What is MeHg?
Pollution due to mercury is widespread in the aquatic environment and occurs both naturally as well as from man-made sources. Levels of Methylmercury (MeHg), the form of the toxin under scrutiny, are increasing and therefore are a major cause for concern. Scientists have traced the pollutant back to coal-burning power plants that release the mercury from their smokestacks to eventually reside in oceans, rivers and even smaller streams. The problem is not that people are ingesting contaminated water, but rather, that they are ingesting fish that live in the polluted aquatic regions. “The infectious cycle is perpetuated as bacteria convert the harmful toxin into an easily absorbable form, which is later consumed by fish.” (PBS: The Mercury Story, 2005) As depicted by the food chain, the smaller animals are eaten by larger predators, which in turn are preyed upon by even larger species. (see visual below) It is then fitting that the largest and oldest species of fish will contain the highest levels of mercury.
(source of image: Google images)
By ingesting fish containing high levels of the contaminant, MeHg is absorbed into the blood stream. As we know with other nutrients and products consumed by pregnant women, MeHg may be passed through the umbilical cord to the developing fetus. One study, conducted by Minoru Yoshida, supports that “Unlike forms of mercury vapor, mercuric mercury, MeHg, is not transferred to the fetus across the placenta.” (Yoshida, 2002) Although tests such as those in Yoshida’s study have shown that MeHg levels are lower in the developing fetus than are those found in the mother, the toxin is still present, thus posing a threat to typical fetal development. MeHg is known to cause damage to the Central Nervous System of a developing fetus, especially during neural migration and differentiation.
Certain fish contain higher levels of mercury than others. The standard guidelines presented by the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are the larger the fish, the higher the level of mercury. “Specifically, these fish include Shark, King Mackerel, Swordfish and Tilefish.” (FDA/EPA, 2004) Please refer to the following site for information regarding mercury levels in various types of fish and shellfish. (http://www.cfsan.fda.gov/~frf/sea-mehg.html) “Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.” (FDA/EPA, 2005)
The “Minamata Disaster”
The story of the “Minamata Disaster” dates back to the early part of the 20th century in a small village called Minamata, located near Kumamoto, Japan. After nearly twenty years in existence, in 1925 a large petrochemical and plastic making company, Chisso Corporation, located on the Minamata Bay, began dumping waste products into the surrounding waters in an attempt to avoid waste removal costs.
“From 1932 to 1968, Chisso Corporation dumped an estimated 27 tons of mercury compounds into Minamata Bay. The town consists of mostly farmers and fisherman. When Chisso Corporation dumped this massive amount of mercury into the bay, thousands of people whose normal diet included fish from the bay, unexpectedly developed symptoms of methylmercury poisoning.”
Due to extensive poisoning from high levels of mercury being transmitted from the fish to the villagers a wide array of symptoms began to develop. Doctors noted the degeneration of the inflicted people’s nervous systems, numbness in the extremities, irregular speech, and impaired vision. Others suffered from lapses of unconsciousness and involuntary movements. It wasn’t until such devastating symptoms began to effect the local population that the source of the pollution, the Chisso Corporation, was identified. This episode in history has come to be known as the “Minamata Disaster” as over 3,000 people have been recognized as being afflicted by the environmental pollution. The case was not taken seriously until the 1960’s when scientists began to study the effects of methylmercury exposure, but since has been a propelling factor in the response from health care professionals on the subject.
(Information and quotations from http://www.american.edu/TED/MINAMATA.HTM)
Recent Research and Discrepancies
One of the most widely known studies on the issue of pregnancy and eating fish was conducted by Constantine Lyketsos and is titled, “Should pregnant women avoid eating Fish? Lessons from the Seychelles”. A longitudinal study of an island population, Lyketsos attempted to determine the effects of high fish consumption by mothers on the developing fetus. To do so, in 1989 he obtained an original cohort composed of 779 mother-child pairs. Based on predetermined geographical constraints the people of the island were, and still are, highly dependent on local fish as a staple of their diet. Compared to the average American woman who consumes 1-2 servings of fish per week, Seychellois mothers consumed an average of 12 servings of fish in a seven-day period. Lyketsos hypothesized that due to such elevated rates of fish consumption the mothers would contain higher than average levels of mercury, therefore passing the toxin on to the developing fetus and causing an increased risk of developmental damage. “Prenatal exposure to MeHg was determined by measuring total Hg in maternal hair growing during pregnancy, the method most indicative of prenatal exposure.” (Lyketsos, 2003) The first centimeter of the mother’s hair was tested and Hg levels were recorded. Later, assessments of neurocognitive, language, motor, memory, perceptual-motor and behavior functions were made for the toxin-exposed children. The children were assessed using such tests as the WISC III (Wechsler intelligence scale for children III), letter-word recognition, various visual-memory tests, and motor functioning tests, among others. They subjects were assessed at the ages of 6, 19, 29 and 66 months of age. Based on the data collected from the Seychellois population in comparison to typically developing children at corresponding ages, there were no adverse effects reported. This paper, published in 2003, assess the original children, this time at nine years of age. Lyketsos’ conclusions support his previous claims that there are no immediate adverse effects displayed by the children due to in-utero exposure to MeHg. One point to note, however, is that “at nine-years-old the children averaged higher scores than typical nine-year-olds on assessments of hyperactivity”. (Lyketsos, 2003) Hypotheses were not made as to why this was the case and as to what implications such a finding may carry. It would then appear based on the study of the Seychelles Island population that increased consumption of fish containing MeHg by the mother has no significant effect on the developing fetus.
Although this study may seem fairly convincing, other studies have shown disagreement among results, thus creating the pending controversy. “Strongly positive results were obtained in a New Zealand study of 74 children born to mothers who ate fish frequently and have elevated levels of hair mercury (i.e. four times the amount of mercury found in the average American mother). This study was constrained by sample size, but found deficits in performance in a range where the Seychelles study reported none.” (Gochfeld et al., 2005) Much of the literature points to this New Zealand population study, however, the paper has thus far been unattainable. However, in the study comparisons were made between the famed Seychelles study, the New Zealand study and data obtained from a population of Inuit peoples in the Artic region. Comparative analysis showed that the highest levels of MeHg, found in the Inuit population, were equivalent to those found during the Minamata Disaster, and were “linked to tremors and impaired muscle tone in newborns”. (Gochfeld et al., 2005) As one can see there appear to be inconsistent findings based on population size and geographic location. There may also be cultural differences and tolerances that are not attributed for in the studies, thus providing the varied findings.
Because it is unethical to implement tests on humans that can potentially be harmful, some researchers have opted to test the effects of mercury and toxicity on other species. Cahanksy et al. decided to observe embryonic development of a crab species, chasmagnathus granulatus from the Rio de la Plata region of South America, after exposing the larvae to mercury. Researchers found increased abnormalities in the sample of larvae exposed to MeHg, including pigmentation defects, enlarged eye-size, abnormal coloration of the eyes. Although such results cannot be generalized to humans based on this crab sample, it seems plausible to conclude that mercury exposure increases the risks of abnormalities and defects. (Cahansky et al., 2005)
What are doctors and officials saying now?
My initial interest in this topic was sparked by a recent edition of Glamour Magazine in which it stated, “In Japan sushi stays on the menu. Here [in the USA] the American College of Obstetricians and Gynecologists (ACOG) says to avoid fish because of parasites, a risk experts told Glamour, is very low. Just eat fish in moderation to avoid mercury exposure,” said Andrei Rebarber, M.D. (Tranell, 2005) After considering much of the current research and consulting U.S. Federal organizations such as the FDA and EPA, it appears that what Rebarber asserts is a consistent belief among doctors in America. The FDA and EPA “are advising women who may become pregnant, pregnant women, nursing mothers, and young children to avoid some types of fish and eat fish and shellfish that are lower in mercury.” (http://www.cfsanfda.gov/~dms/admehg3.html) Also, it is recommended that women eat no more than one 12 oz. serving of low mercury containing fish, or two 6 oz. servings per week. A common concern among pregnant women is eating canned tuna fish. It has been supported that albacore “white” tuna has more mercury than does its counterpart “light canned tuna”, and it is therefore suggested that women eat the canned version instead of a fresh albacore steak. Also, the FDA and EPA are attempting to initiate programs to remove mercury from power plant emissions. Such programs, however, are expected to cost between two and six billion dollars.
Not surprisingly, major fisheries in the United States have been up in arms, denying accusations and assertions made by government agencies about the potential dangers of mercury in fish. A perfect example of this is seen in the U.S. Tuna Foundation. In 2004, the Foundation issued a press release stating that “New Evidence Shows Benefits of Eating Fish During Pregnancy”. Of course, the Foundation then cites data showing that the intake of Omega-3 fatty acids is beneficial to the developing fetus, a peripheral issue that was not being questioned in regard to mercury intake. They also state that mercury levels in American women were low and unrelated to neurodevelopment, also not the pertinent issue. After completion of a study on “childhood development at 15 and 18 months, the study found a subtle but consistent link between eating fish during pregnancy and a child’s early cognitive development, even after adjusting for factors such as age and education of the mother, whether she breastfed, and the quality of the home environment.” (US Tuna Foundation, 2004) The study attempted to say that eating canned tuna caused children to perform better on cognitive tasks, but was rather unfounded. Although these findings may appear strong the cautious reader should take into account other issues that may have confounded the results, as there are certainly variables that were not controlled for. (http://www.tunafacts.com/press/2004/july14.cfm)
The presented studies on fish consumption during pregnancy show just how controversial the issue really is. As with any controversial topic it is furthered by ultra-conservative groups such as the Environmental Health Unit of Maine. This association puts out warnings across the state of Maine stating that pregnant women should NEVER eat fish in order to protect their unborn child. Of course this is a radical perspective, but again, displays the concern of mercury exposure on the fetus. The agency does validate their claims by listing specific examples of possible damages due to the toxic exposure including paresthesia, constriction of visual field, intention tremor, impairment of hearing/speech, and mental disturbances such as decreased cognitive functioning. (Information from http://www.maine.gov/dhhs/ehu/fish/)
Interviewing an OB/GYN
While conducting research on this topic I was lucky enough to be able to speak with my own physician, Dr. Richard Reuben, M.D., and find out what he is currently advising his patients in regard to consuming fish while carrying a child. Most of what he said agreed with what the FDA and EPA presented. He stated that he advises pregnant women to “avoid eating fish containing high mercury levels, including shark, swordfish, tilefish, and king mackerel.” He asserted that although many physicians may not inform their patients, there is an increasing concern about mercury levels raising in salmon and tuna, therefore Dr. Reuben advises women to maintain a very low intake of such fish. It is important to note that salmon and tuna were not historically considered high-risk fish, but the threat is growing. Reuben recommends no more than 12 oz per week of well-cooked fish. “If this regime is followed,” he states, “MeHg absorption should not be a problem.” (Reuben, 2005) He also said that an estimated 60,000 babies are affected each year worldwide. Most frequently they suffer from damage to the Central Nervous System and decreased cognitive functioning. I raised the question of the importance of obtaining Omega-3 Fatty Acids, which are contained in fish, and his response was to weigh the risks versus the benefits. “Although Omega-3 Fatty Acids are important and are known to reduce depression in the mother by synthesizing serotonin in the brain, they can be taken in the form of a daily supplement, diminishing the need for large amounts of fish.” Interestingly, he brought up the issue of cultural disparities on the subject, specifically that women in Japan continue to eat sushi throughout their pregnancy, as Glamour also mentioned. About this he simply stated, “I prefer to err on the side of caution.” No clear understanding has been reached as to why women in some areas continue to eat fish whereas other women do not.
The issue of eating fish while pregnant is a complicated one that seems to elicit differing responses depending on who you consult. After considering various sides of the debate I believe that a medium needs to be struck. In a general sense, continued consumption of sushi during pregnancy in the Japanese population does not seem to be producing an increase in birth defects. However, I would not suggest disregarding all medical advice presented here in the U.S. Cases such as the “Minamata Disaster” seem proof enough that extremely high levels of MeHg can be quite damaging to the unborn baby as well as to the mother. The FDA and EPA recommendations as well as the case presented by Dr. Reuben seem reasonable given what data we have on the subject. With future research and analysis, there is a possibility that cultural differences will one day be understood, but until then, it seems that doctors and women will continue to follow the medical recommendations presented in their region.
PBS: The Mercury Story, January 2005
Food and Drug Administration/Environmental Protection Agency
Environmental Health Unit of Maine
US Tuna Foundation
American University: The “Minamata Disaster”
Cahansky, A.V., Lopez Greco, L.S., Sanchez, M.V., Rodriguez, E.M. (2005). Toxicity of
Mercury during the embryonic development of chasmagnathus granulatus.
Environmental Research. 99, 72-78.
Gochfeld, M., Burger, J. (2004). Good Fish/Bad Fish: A composite benefit-risk by dose
curve. NeuroToxicology. 26, 511-520.
Lyketsos, C.G. (2003). Should pregnant women eat fish? Lessons from the Seychelles.
The Lancet. 361.
Trannell, K. (2005). Do I really have to give up sushi? Glamour. p. 182.
Yoshida, M. (2002). Placental to fetal transfer of mercury and fetotoxicity. The Tohoku
Journal of Experimental Medicine. 196, 79-88.
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