Mercury is a metal found naturally in the environment. Human activities, such as farming, burning coal, and using mercury in manufacturing, increase the mercury cycling through the air, water, and soil. In water, mercury changes its form and becomes methylmercury. Fish absorb this mercury. When you eat fish containing mercury, you absorb the mercury, and at high levels it can be harmful. Mercury will leave the body over time in the urine, feces, and breast milk.
For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart health and children's growth and development.
Nearly all fish and shellfish contain traces of mercury. But some contain high levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. In a fetus or young child, this can damage the brain and nerves (nervous system).
Because of the mercury found in fish, Health Canada recommends that people eat limited amounts of fish high in mercury. Certain people need to limit high mercury fish even more, including:
If you are concerned about your or your child's mercury level, talk to your doctor or local health unit about testing.
Most people should not eat more than 150 g (5 oz) per week of fish that are known to have higher mercury levels. These include fresh or frozen tuna (not canned "light" tuna), shark, swordfish, marlin, orange roughy, and escolar. Some people need to restrict high-mercury fish even more:footnote 1
Most Canadians don't need to limit how much canned (white) albacore tuna they eat each week. But women who are or may become pregnant, nursing mothers, and children need to limit canned albacore tuna intake to no more than:
Health Canada has no restrictions on eating fish and shellfish that are lower in mercury. These include salmon, rainbow trout, pollock, herring, shrimp, mussels, clams, oysters, and canned "light" tuna.
Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas.
Mercury accumulates in your bloodstream over time and slowly leaves the body through urine, feces, and breast milk. If you eat a lot of fish high in mercury, it may take up to a year for your mercury levels to drop after you stop eating the fish. If you decide to become pregnant or if you have an unplanned pregnancy, you may have high levels of mercury. While elevated levels of mercury usually do not cause significant health problems, they may affect a developing fetus. If you are of childbearing age, try to follow the guidelines above when you eat fish.
For specific information on your province's or territory's fish consumption advisories, see www.ec.gc.ca/mercure-mercury/.
For general information on mercury in fish, see:
Health Canada (2008). Mercury in fish: Consumption advice: Making informed choices about fish. Available online: http://www.hc-sc.gc.ca/fn-an/securit/chem-chim/environ/mercur/cons-adv-etud-eng.php.
Current as ofSeptember 5, 2018
Author: Healthwise StaffMedical Review: Sarah A. Marshall, MD - Family MedicineBrian O'Brien, MD, FRCPC - Internal MedicineAdam Husney, MD - Family MedicineKathleen Romito, MD - Family MedicineSiobhan M. Dolan, MD, MPH - Reproductive GeneticsKirtly Jones, MD - Obstetrics and Gynecology, Reproductive Endocrinology
Current as of: September 5, 2018
Sarah A. Marshall, MD - Family Medicine & Brian O'Brien, MD, FRCPC - Internal Medicine & Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & Siobhan M. Dolan, MD, MPH - Reproductive Genetics & Kirtly Jones, MD - Obstetrics and Gynecology, Reproductive Endocrinology
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