At the April 2017 meeting of the American Academy of Neurology, a research paper was presented that suggests a link between the intake of certain types of fish, their mercury content, and the increased risk for Lou Gehrig’s disease (ALS). The study included 294 individuals with ALS and 224 individuals without ALS.

Researchers estimated mercury exposure of the two groups by referring to tables of the mercury content of various fish, and by evaluating mercury levels in subjects’ toenails: a reliable marker of long-term mercury ingestion. The study showed that those in the top 25% for estimated annual mercury intake were at double the risk for ALS, compared to those in the lower levels.

What issues occur in the person affected by ALS condition?

In ALS, the motor neurons that control muscle function deteriorate, leading to progressive muscle weakness and paralysis throughout the body. Most people only live 2-5 years after the onset of the disease. Scientists are slowly making progress as to what causes this disease, but toxic substance accumulation has been identified as one of the factors associated with it.

How eating fish increases the risk factor of mercury consumption?

When it comes to mercury exposure from fish and seafood, which are the main dietary sources that tend to affect us, there are a few key things to know:

1. Thousands of tons of mercury are released into the air each year through pollution and waste. Bacteria and natural processes can transform mercury into the organic mercury compound methylmercury (MeHg), which is a poisonous substance.
   Methylmercury can accumulate in streams and oceans. Unfortunately, this toxin is in the fish we eat. It also accumulates in the food chain, as each fish absorbs all the mercury of the smaller fish or organisms it has eaten. That is why the oldest and largest fish, such as shark or swordfish, have the highest levels of methylmercury.
2. In March 2004, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) issued a joint Consumer Advisory, warning about methylmercury in fish. The advisory was intended for women who might become pregnant, are pregnant or nursing, and children.

Here are a highly valuable recommendation for pregnant/nursing women and children

• Avoid eating shark, swordfish, king mackerel, and tilefish (also known as golden bass or golden snapper)

• Limit consumption of all other types of fish to 12 ounces per week.
• Limit the consumption of canned albacore (“white”) tuna or fresh tuna to no more than 6 ounces per week.
• Limit the fish eaten by young children to even smaller portions per week.
• Check local advisories about the safety of fish caught in local lakes, rivers, and coastal areas. If no advice is available, eat no more than 6 ounces per week of locally caught fish, and do not consume any other fish during that week.
• If more than the recommended amount of fish is eaten in one week, eat less in the following weeks.

There was a 2017 update provided by the EPA and FDA, which also included a chart to simplify the list of Best Fish Choices, Good Fish Choices, and Fish to Avoid. I have included a link to this chart in the text below. 

As a quick and easy reference, I have also included a list of fish to be avoided and the ones that are safer to consume in the text below. In general, having two, maybe 3 servings of safer fish each week, is one way to get higher amounts of desirable omega-3 fats.

How can we limit the fish intake from our daily diet chart?

Because we need to limit our fish intake to this degree due to the risk of mercury accumulation, many experts suggest that we also take an omega-3 fat supplement each day that includes fish and/or flaxseed oil, to help optimize important omega-3 fat status in the body. Omega-3 fat supplements are virtually devoid of any mercury or other contaminants, making them a safe option to boost omega-3 fat nutritional status.

Benefits of Omega-3 Supplements

As you probably know, omega-3 fats are quite important in cardiovascular health, in suppressing inflammation, in possibly reducing cancer risk, and certainly for brain health and the prevention of Alzheimer’s disease. So, it’s good to have an omega-3 fat strategy, just not one that also comes with the price of mercury accumulation in your body. The latest study suggests a link to Lou Gehrig’s disease, but mercury is toxic to the nervous system in general.

Check out the list of safe and unsafe fish in the text below, along with scientific references that I have also included.

Fish High In Mercury to Avoid:

• Shark
• Swordfish
• King Mackerel
• Tilefish (a.k.a. golden bass, golden snapper)

Lower in mercury but still to be avoided:

• Tuna steak (also used in sushi and sashimi)
• Canned Albacore white tuna

Fish to be eaten in limited quantities by women who are/may be pregnant or nursing, and young children:

Canned light tuna Sea bass Gulf Coast oysters Eastern Oyster Marlin Halibut Channel catfish (wild)

Haddock Mahi-mahi Largemouth bass Blue mussel Cod Pollack Gulf Coast blue crab

Pike Great Lakes salmon Lake whitefish White croaker Walleye

Fish lowest in methylmercury:

Catfish (farmed) King crab Scallops Fish sticks Flounder (summer)

Trout (farmed) Salmon (wild Pacific) Shrimp Tilapia Sardines

References:

1. https://www.fda.gov/food/consumers/advice-about-eating-fish
2. http://www.nutraingredients-usa.com/Suppliers2/Continued-buzz-about-mercury-in-fish-could-bolster-omega-3-supplements

Eat Smart, Live Well, Look Great!

Dr. James Meschino