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Family Health Magazine - MODERN LIVING

Is Seafood Safe?
Questions and answers about mercury in fish

Concerns about mercury levels are making many Canadians reluctant to eat fish. Canada’s Food Guide recommends that anyone aged two and older eat at least two servings of a variety of fish each week. However, we tend to eat just over three fish meals in a month. Are possible toxins a good reason to bypass the benefits of fish?

Why eat fish?

Fish is a source of many important nutrients. It contains high quality protein, is low in saturated fat, and is one of the best food sources of omega-3 fatty acids. These essential fats help with heart health and brain development. They have been shown to reduce blood clots, blood pressure and irregular heart rhythms while improving artery health. Omega-3 may even help lower levels of depression and mental illness.

Omega-3 fatty acids are crucial to the developing nervous system. They are especially important for young children, pregnant women and their unborn babies.

Fish is a good source of vitamin B12. Other minerals in fish, including selenium, iodine, magnesium, iron and copper, are needed for growth and tissue repair.

Why is mercury a problem?

Mercury occurs naturally in the environment. Weathering, volcanoes and forest fires can all release it from soil and rocks. It is found in lakes and oceans. Human activities, such as burning fossil fuel, are also releasing mercury.

Since plants do not take up much mercury from soil, levels in fruits and vegetables are very low. However, micro-organisms in water absorb mercury to create an organic version. This form, called methyl mercury, attaches to proteins in fish. The amount a particular fish will absorb will depend on where it is and whether it eats other fish.

Why should I care about mercury levels in my food?

Low levels of mercury, even long term, should not significantly affect the health of most people. It is thought that these risks are outweighed by the health benefits of eating fish.

However, high levels of mercury can damage the nervous system. The developing nervous system in particular is very sensitive to the effects of mercury. Mercury can affect attention, verbal learning, fine motor and memory skills in babies and growing children. Kids should be exposed to as little as possible. Women of childbearing age, especially those who are pregnant or breastfeeding, will also want to be cautious.

Why is mercury a problem in some fish but not others?

The age, size and species of a fish affect the mercury content. All fish contain some mercury. However, fish that eat other fish, and fish that are larger and older tend to contain more. For these reasons, large predatory fish such as shark, marlin, and swordfish, are relatively high in mercury.

In turn, fish are the main way most Canadians take in mercury. Keep in mind that some fish have very low levels. Eat these types as often as you like, while eating species with higher levels less often. Remember, including fish low in mercury as part of your diet has many health benefits. The information in Tables 1 and 2 can help you decide on what type and how often to eat fish.

What else do I need to know?

• Cleaning, preparing and cook­ing fish will not remove or reduce the amount of mercury in fish.
  
• We do not yet have enough information about mercury levels in all types of fish in all regions. If you like a type of fish that is not included in this list, keep the amount you eat low. Instead, eat a wide variety of fish.
  
• Mercury levels in the body can increase over time and will not drop suddenly if mercury exposure is eliminated or reduced. It can take over a month for levels in the blood to drop significantly. For this reason, all women of childbearing age should watch their consumption of mercury-containing fish, even if they are not pregnant or planning to become pregnant soon.

Fish is a healthy food for you and for your family. It offers an excellent source of nutrients for pregnant women and their developing babies, for growing children, and for the population in general. It is possible to enjoy fish as a regular part of your diet without exposing yourself or your family to harmful levels of mercury.

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While effort is made to reflect accepted medical knowledge and practice, articles in Family Health Online should not be relied upon for the treatment or management of any specified medical problem or concern and Family Health accepts no liability for reliance on the articles. For proper diagnosis and care, you should always consult your family physician promptly. © Copyright 2019, Family Health Magazine, a special publication of the Edmonton Journal, a division of Postmedia Network Inc., 10006 - 101 Street, Edmonton, AB T5J 0S1    [ML_FHb08]