Pregnancy and the dangers of mercury

According to a study from Consumer Reports, pregnant women should avoid all tuna due to the dangers of being exposed to high levels of mercury. This contradicts the FDA’s recommendation made in June stating that women who are pregnant may consume up to 12 ounces of fish per week. But while fish is a great source of lean protein and omega-3 fatty acids, larger fish – such as tuna - contain high and unsafe amounts of mercury. Consumer Reports says that these amounts of tuna are to be avoided by women who are in any of the three categories: pregnant, thinking about becoming pregnant, or breast-feeding.

Fish is a major source of omega-3 fatty acids, low in saturated fat, and high in protein, vitamin D, and other nutrients – all of which are important for both the development of a healthy baby and in the health of the mother. However, fish also contains mercury – a contaminant that when consumed in excess amounts, is dangerous for a baby’s growth and development. Tuna – specifically, canned tuna – happens to be one of the most commonly consumed fish in the United States. Despite its reputation to be a low calorie and tasty meal, there are actually 60 micrograms of mercury in canned albacore tuna. This is compared to a 4-ounce serving of salmon which contains about 2 micrograms of mercury, and swordfish, which contains 150 micrograms of mercury.

Mercury contaminates fish via natural and man-made sources such as emissions from coal-fired power plants. When mercury finds its way into lakes, rivers, and oceans, bacteria convert it to methylmercury – a neurotoxin which can affect the brain and nervous system – which is absorbed by fish through the water they swim in or consumed by what they eat. Once the mercury makes its way into the marine food chain, it is accumulated by the larger predators – hence why larger fish are riskier to eat than smaller fish. Methyl mercury also binds tightly to the proteins in fish muscle and can remain there even after the fish is cooked - making raw and cooked fish a concern. Babies, including those in utero, and young children are the most vulnerable to high levels of mercury because of their still developing brain and nervous system.  

When we eat fish, methylmercury can be easily absorbed through our digestive tract. Because of this easy access, when a woman is pregnant, methylmercury can cross the placenta and makes its way into the womb. When a woman is breast-feeding, it can reach the baby through the consumption of breast milk.  And when a woman is trying to get pregnant, it is important to be concerned about mercury exposure even then because accumulated mercury in our bodies takes time to go away.

In the United States, one out of every six children are born each year having been exposed to mercury levels so high that they are at risk for learning disabilities, motor skill impairment, and short-term memory loss. Studies show that when the womb is exposed to high levels of methylmercury, a baby’s growing brain and nervous system can be impaired. According to the Environmental Protection Agency (EPA), cognitive skills such as memory and attention, motor skills, vision, and language may be impaired. Therefore, Consumer Reports states that women who are pregnant, thinking of becoming pregnant, or breast-feeding, as well as their babies and young children, should avoid tuna and all fish that contain high levels of mercury.

In addition to avoiding tuna, the FDA and Consumer Reports advises to avoid other high mercury fish such as:

·       Swordfish

·       Shark

·       King mackerel

·       Gulf tilefish

·       Marlin

·       Orange roughy

So what are the alternatives for people who want fish in their diet but want to avoid consuming an unsafe amount of mercury? Consumer Reports recommends eating the following fish about two to three times a week:

·       Tilapia

·       Wild Alaskan salmon

·       Shrimp

·       Scallops

·       Sardines

·       Squid

·       Oysters