Mercury is an environmental toxin which is often concentrated in fish. Mercury toxicity is most commonly found in infants and can trigger a number of developmental problems due to its effect on nerves. While tuna are a rich source of nutrients, such as omega-3 fatty acids, women who are considering becoming pregnant, who are pregnant or who are lactating should ensure that they consume tuna within a safe range to reduce the risk of mercury toxicity in their children.
Mercury and Fish
Nearly all fish contain some amounts of mercury, but these amounts are usually not harmful, the U.S. Food and Drug Administration reports. Methylmercury is the form of mercury that accumulates in fish. Mercury is also released into the air in the form of air pollution. Why mercury is concentrated in fish is not completely known as of 2011. According to the U.S. Geological Survey, certain bacteria capture mercury from the environment and turn it into methylmercury. These bacteria are consumed by different organisms in the food chain, until it reaches fish, where the mercury is concentrated the most.
Signs and Symptoms of Toxicity
The risk of mercury toxicity is greatest in very young children and infants; for this reason, pregnant and lactating mothers are advised to be careful when eating seafood. The symptoms depend on the type of mercury consumed. Methylmercury is most toxic to nerves; children affected with mercury poisoning may experience abnormal brain development. "Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methylmercury in the womb," the U.S. Environmental Protection Agency notes. Methylmercury may also cause impairment of vision, a sensation of tingling extremities, impaired speech and unsteady gait.
Mercury Levels
The Environmental Protection Agency sets limits on the level of methylmercury contamination considered acceptable in foods. However, "Consumer Reports" magazine warned in 2011, the amount of contamination in most commercially sold foods exceeds these amounts. The study found that women exceeded the safe amount of mercury consumption by eating a single serving of canned white tuna or two servings of light tuna a week. Because of this, the magazine advised that women who are considering having children, are pregnant or who are lactating should avoid tuna products altogether.
Avoiding Mercury Toxicity
Despite the concerns of mercury contamination, the Centers for Disease Control and Prevention maintained as of 2010 that mercury levels in most people are within safe limits. The Food and Drug Administration recommends that women who are considering having children eat canned light tuna, which has lower mercury content, and should have no more than 12 oz. of tuna per week. Women are advised to check with local advisories regarding mercury contamination before consuming locally caught fish.
References
- U.S. Food and Drug Administration; What You Need to Know About Mercury in Fish and Shellfish; March 2004
- U.S. Geological Survey; Mercury in the Environment; October 2000
- U.S. Environmental Protection Agency: Mercury: Health Effects; Oct. 1, 2010
- "Consumer Reports" magazine; Mercury in Canned Tuna Still a Concern; January 2011
