Methyl Mercury and the Three Omega 3's

Note: This is an article I wrote for the Well Fed Network last spring. It is long and somewhat technical, but I feel it is important, which is why I've chosen to re-publish it here. Omega 3 fatty acids are very important in the development and maintenance of the central nervous system (CNS). This is well understood by the general public, however the effect of methyl mercury (in fish sources of omega 3s) on the adult CNS is often down-played or ignored. Fetuses are particularly vulnerable to accumulating mercury, and this can impact their development even when the mother has only a moderate intake. I checked all of the links and some of them needed to be updated. As certain medical journals have a tendency to move articles around in cyberspace, I have chosen to use a more formal (but as brief as possible) citation on updated links, so they will be easier to track down should they go missing in the future.

Once upon a time obtaining dinner meant picking a few berries off that shrub over there, and spearing a salmon out of the stream. Then we got it in our heads that we might want to keep a chicken around for a reliable source of eggs and maybe tend a patch of wheat. Now it means grabbing a pre-packaged, chemical cocktail wrapped in plastic. Slowly our diets have changed drastically from wild foods to cultivated foods to genetically modified and chemically adulterated foodstuff. Along the way, we have lost access to vital nutrients, including healing fats.

Essential fatty acids are those fatty acids that the body cannot synthesize from other dietary components; therefore they must be included in the diet. There are two such fatty acids – omega 3 and omega 6. Omega 3 refers to the position of the first unsaturated (double) bond in the fatty acid. There are three molecular forms of Omega 3 – eicosapantaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA). EPA and DHA are known as the long forms, as their structures contain longer fatty tails with 5 and 6 double bonds respectively. They appear to be found in nature mainly in marine life forms, such as marine algae, kelp, and the fish associated with such ecosystems. ALA is structurally known as the short form, as it contains only 3 double bonds on a shorter fatty tail. Common sources of ALA are terrestrial plants such as grasses, flax seeds, and wild greens; as well as the animals which graze upon them, such as free-range chickens, cows, etc. While it is possible for the human body to convert ALA to EPA and DHA, the conversion is far from efficient.

The modern human’s diet is grossly deficient in omega 3 fatty acids, while simultaneously gluttonous upon omega 6 fatty acids (the other essential fatty acid). This imbalance in essential fatty acids has been linked to the increased risk of cardiovascular disease, cancer, as well as autoimmune and inflammatory diseases. An ideal healthy ratio of omega 3:omega 6 is in the range of 1:2 to 1:4, while the average American’s profile is 1:15 or worse. What are the root causes of this imbalance? Primarily our food cultivation practices. Wild plant foods are much higher in ALAs than cultivated varieties. The practice of feeding farm animals with corn and grains, rather than allowing them to free-range in pastures skews their essential fatty acid composition. Fish farming contributes as well, because farmed fish cannot forage on foods rich in EPAs and DHAs and most fish farmers feed their fish grains. Another contributing factor is our heavy reliance on cooking oils which are high in omega 6s such as corn, soy, cottonseed, and peanut.

With the increasing awareness of the importance of omega 3 fatty acids, more and more products are sporting omega 3 labels. Omega 3 eggs come from chickens fed flax seeds. Flax seeds and flax oils are being added to many products. But remember that products based upon flax oils will mostly contain ALA and not EPA or DHA, which appear to be more important to human health. According to the Institute of Medicine, “ALA is not known to have any specific functions other than to serve as a precursor for synthesis of EPA and DHA.” However, it is interesting to note that cultures with high ALA consumption are also those known for the greatest longevity.

Regular consumers of animal products, including dairy products, would be doing themselves a favor by purchasing products from free-range, grass-fed animals. Not only are the animals treated more humanely, but their bodies have a more balanced essentially fatty acid profile, the benefits of which get passed on to the consumer. Any actions you can take to re-balance your omega 3:omega 6 ratio should benefit your long-term health. For those who choose to avoid fish, there is some good news, as it appears that so long as your omega 3 to omega 6 ratio is 1:4, your ability to convert ALA to EPA will be optimized. Further evidence shows that if your diet is high in saturated fat, as opposed to omega 6s, your conversion rate may be as high as 6% for EPA and 3.8% for DHA. (International Journal for Vitamin and Nutritional Research, 3/1998, Gerster, "Can Adults Adequately . . .") That’s up to 50% greater conversion than for a diet high in omega-6 fatty acids.

Several recent studies confirm the hypothesis that omega 3 fatty acids, specifically EPA and DHA, can inhibit the growth and discourage the spread of certain cancers. Additionally, conjugated linoleic acids, which are found in higher percentages in the meat and dairy products of grass-fed animals, have been shown to significantly reduce cancer risk.

There seemed to be clear evidence that EPAs and DHAs also improve cardiovascular health, until recently. According to Dr. Mike Knapton, director of prevention and care at the British Heart Foundation, this uncertainty may be due to the effect of methyl mercury being thrown into the equation. Methyl mercury has been shown to diminish the positive effects of omega 3 consumption on heart health. Specifically methyl mercury can increase the risk of heart attack, and can lead to thickening of the major arteries that lead from the heart to the brain, in addition to encouraging accumulation of plaques in these arteries.

Omega 3 fatty acids contribute to brain cell development and maintenance. DHA is an important component of neuron membranes, where it facilitates ion exchange necessary for signal transmission. DHA deficient diets appear to lead to decreased neuron size and reduced spatial memory in developing brains (Nutritional Neuroscience, vol 5 #2 2002, 103-113, Ahmad et. al., “A Decrease in Cell Size . . .”). There is some evidence that low DHA levels are further linked to depression, memory loss, attention deficit disorder, and an increased risk of Alzheimer’s. One study, currently in progress in the UK, suggests that omega 3 supplementation may ameliorate the symptoms of Attention Defecit Disorder. However, fish consumption again looks like a two-edged sword, because mercury has a degenerative effect on neurons, potentially causing neurological problems in the developing brains of children. Adults should also be concerned, because methyl mercury accumulates in the brain, and elevated blood mercury levels appear to be associated with Alzheimer’s. Chronic low doses of methyl mercury may lead to accelerated brain aging later in life.

If you would prefer to benefit from the protective effects of omega 3 long chain fatty acids, without worrying about exposure to methyl mercury, there are a few options. To just minimize your mercury exposure, choose fish lower in mercury content. Fish oil supplements may be a better way to avoid mercury altogether, as many of the supplements have tested negative for mercury in the past. If you are vegetarian, look for DHA eggs, from chickens fed fish oils or marine algae, or else find recipes that incorporate fresh kelp.