The Risks and Benefits of Seafood for Sensitive Populations

<p>NON-TECHNICAL SUMMARY: Infants are exceptionally sensitive to the adverse long-term health effects from exposure to environmental toxicants. Exposure to methylmercury, a developmental toxicant found primarily in fish, has been predicted to negatively impact the health of 400,000 newborns every year in the United States, with adverse effects (abnormal memory, attention and language skills) possibly lasting past childhood. Pregnant or nursing women need to consume seafood because it is nutritionally important and provides lipids which promote healthy brains and eyes during perinatal development. Since maternal transfer of mercury and omega-3 fatty acids are the primary routes for fetal (placental transfer) or infant (maternal milk) exposure/nourishment, there is a critical need to communicate specific advice to childbearing-aged women.Fifty years ago, the debilitating effects from exposure to high levels of mercury were documented during the Minimata Bay (Japan) incident (NRC, 2000). However, the effects of low level mercury exposure on the developing brain are still being determined. Grandjean et al. (1999) reported that excessive exposure to methylmercury when in the womb caused sustained deficits in language, attention, memory and fine-motor function that were measurable at 7 years of age for children living in the Farao Islands. Davidson et al. (2008) reported an adverse association between mercury exposure and Psychomotor Developmental Index score at 2.5 years of age for children living in the Republic of the Seychelles. The toxic effects of methylmercury have been reported in American adults by Hightower and Moore (2002). They found that adult patients living in San Francisco, who were high-end consumers of large marine species, experienced symptoms of mercury toxicity (including fatigue, headache, decreased memory, decreased concentration, muscle and joint pain) which receded following removal of these species from their diets. Some children of these patients were found to have mercury levels that were 40 times higher than the national average. </p><p>Nationally, the CDC (2004) using the National Health and Nutrition Examination Survey (NHANES) estimates that ~6% of childbearing-aged women in the United States have whole blood mercury levels that exceed the safe limit of 5.8 µL/L. Mahaffey (2004) predicted that 10% of babies born in the United States have been exposed to unsafe levels of mercury. Maas et al. (2004) tested hair from nearly 1,500 people in the United States and reported that 21% had mercury concentrations exceeded 1 ppm which is considered the safe limit based upon the Environmental Protection Agency's Reference Dose (RfD = 0.1 µg/kg body weight-day).The Environmental Protection Agency (NESCAUM, 2005) has estimated that canned tuna contributes 34% of the mercury to which Americans are exposed. Certain segments of the population (i.e., infants from low income families) may be at increased risk because of federal assistance programs which provide canned tuna to lactating women. The USDA's Special Supplemental Nutrition Program for Women, Infants and Children (WIC) provides resources to ~8 million low-income women including services that aid ~50% of all infants born in the United States. Lactating women frequently obtain canned tuna which may contain moderate amounts of mercury (i.e., Albacore and Yellowfin tuna) through WIC vouchers (USDA-FNS, 2004). Salmon is a better choice since it provides higher amounts of healthy fats and is lower in environmental pollutants (i.e., mercury and PCBs) than most canned tuna products.While the solution to reducing mercury exposure may seem as simple as recommending that pregnant or nursing women avoid eating fish, one should not underestimate the importance of fish as part of a healthy diet. Oken (2005) reported a 4-point increase in visual recognition memory in infants which was associated with a higher maternal seafood intake; however, an increase in mercury intake from fish was associated with a decline in the visual memory recognition score. The Harvard Project (2005) examined the risks and benefits and concluded, "that if pregnant women were to eat the same amount of fish but replace fish high in mercury with fish low in mercury, cognitive development benefits, amounting to about 0.1 IQ points per newborn baby, could be achieved with virtually no nutritional losses."Our research group is just completing a clinical trial to develop dietary recommendations which are aimed at optimizing the nutritional benefits from consuming fish while also minimizing the relative risks to sensitive populations. Our group surveyed 721 low-income women (of which 35% were pregnant and 5% were nursing), from across Indiana. Thirty-nine percent reported that they had not eaten commercial fish within the past month and 10% of fish eaters had consumed fish that contains moderate to high levels of mercury (tuna steak, shark, swordfish or king mackerel). Only 33% understood that the omega-3 fatty acids in fish are nutritionally important for the health of the unborn child and nursing infant. </p><p>The Dietary Guidelines Advisory Committee (2004) recommended that adults consume 8 ounces of fish every week. Unfortunately, there are very few fish species (herring, mackerel, sablefish, salmon, shad and whitefish) which provide the desired amount of the long-chain omega-3 fatty acids (EPA and DHA) at the recommended consumption rate. King mackerel, which is much higher in mercury than canned Jack mackerel, and sablefish are both higher in mercury. Based upon the top ten most frequently consumed seafoods, it is more likely that consumers, who attempt to follow the dietary recommendation to simply 'eat fish', will increase their intake of mercury without increasing their intake of long-chain omega-3 fatty acids.The USDA reports nutrient information for ~57 species; however, it is difficult to determine the origin, size or age of the fish, or the date of sampling. Nutrient concentrations can vary dramatically for farmed fish because fatty acid concentrations in the edible tissue are affected by feed composition and energy status. It has been reported that after the PCB controversy in farmed salmon (Hites et al., 2004), that producers changed the composition of their feed to reduce PCB residues (Friesen et al., 2008). PCBs that were reported in the farmed salmon were unintentionally added when fish oil, an excellent source of omega-3 fatty acids, was added to the feed. Changes in feed composition can have a dramatic effect on nutrient composition. Accurate and current lipid composition data, which can change over time, are critical for nutritional assessments and consumption advice. Likewise, the FDA mercury data is limited because it does not provide the size or age of the fish or the locations from which the fish were grown. These factors can have a significant effect on mercury residues which are directly affected by fish age and dietary exposure.Recent controversies surrounding the safety of fish have many healthcare professionals questioning the overall risks and benefits from fish consumption. Within the past several years, news stories have reported on the safety of farmed salmon that contains PCBs, flame retardants and pesticides; catfish that contain dioxins; and tuna, swordfish, king mackerel, shark and tilefish that contain mercury. It is essential that childbearing-aged women consume 8-12 ounces per week and that they make an informed decision to select fish which are lower in pollutants and higher in omega-3 fatty acids. Communicating this multi-pronged message to consumers can be challenging. There is a need to improve and validate current dietary recommendations regarding seafood consumption and deliver the resulting science-based dietary recommendations to consumers. </p>