| Seventy five years ago, long chain polyunsaturated | | | | proteins, it is found throughout fish tissue, including |
| oils (PUFA also known as polyunsaturated oils) were | | | | muscle tissue that makes up fish steaks and fillets. |
| added to the list of essential nutrients. Since then | | | | Fish can also absorb organic chemicals (such as PCBs, |
| there have been many publications reporting low | | | | dioxins and DDT) from the water, suspended |
| rates of death from coronary heart disease (CHD) | | | | sediments, and their food. |
| among Greenland Eskimos due to fish consumption. | | | | In humans, health effects of very high mercury |
| Today, fish is considered a health food. Now, we all | | | | exposure following occupational or industrial accidents |
| know the importance of eating fish to obtain the | | | | include paresthesias, ataxia, and sensory abnormalities |
| daily and much needed omega-3 oils into our modern | | | | in adults, and delayed cognitive and neuromuscular |
| day diets not only in the prevention of CHD but also | | | | development following exposure to the unborn child. |
| in preventing sudden death from this disease. | | | | Health effects of chronic low level mercury exposure |
| The omega-3 polyunsaturated oils: eicosapentaenoic | | | | seen with fish consumption are less well established. |
| acid (EPA also known as 20:5 omega-3) and | | | | The public is aware of the potential harm from |
| docosahexaenoic acid (DHA also known as 22:6 | | | | mercury in fish but lacks clear understanding of who |
| omega-3) found in fish are linked with optimal brain | | | | is at risk or which seafood species contain mercury. |
| function, cognition, and improved eye and skin health. | | | | Adult men, and women who are not planning to |
| Some studies, furthermore, show that although some | | | | become pregnant, are less at risk from mercury |
| omega-3 oils may be protective against certain | | | | exposure than children. Methylmercury crosses the |
| cancers and may have a therapeutic effect on | | | | placenta, and foetal exposure correlates with |
| depression and specific autoimmune diseases including | | | | maternal exposure. Methylmercury is a neurotoxicant |
| lupus erythematosis, psoriasis, and arthritis yet other | | | | and high exposures over long periods of time may |
| omega-3 oils derived from certain other sources can | | | | adversely affect the developing foetal brain and |
| actually increase the risk of certain types of cancers. | | | | central nervous system. It can take 5 years or more |
| This is because the omega 3 oils obtained from | | | | for women in their childbearing years to rid their |
| vegetable origin (α-linolenic acid) is a precursor | | | | bodies of PCBs, and 12-18 months to significantly |
| of long chain polyunsaturated omega-3 as found in | | | | reduce their mercury levels. |
| fish and the endogenous conversion of | | | | Recent work shows public confusion about the |
| α-linolenic acid in the human body to EPA and | | | | benefits of fish, challenged by the evidence of |
| DHA is limited and inefficient. Therefore the source of | | | | mercury and other contaminants in fish, resulting in |
| omega-3 fatty acid can influence a disease outcome. | | | | controversy and confusion over the role of fish |
| When comparing different types of fish, lower risk | | | | consumption in a healthy diet. The low levels of |
| appears more strongly related to intake of oily or | | | | pollutants in oily fish that can build up in our bodies, |
| fatty fish (salmon, herring, sardines, mackerel), rather | | | | pregnant and breastfeeding women, girls and women |
| than lean fish (cod, catfish, halibut). Some common | | | | who one day may have a baby are advised not to |
| fish that contains high levels of omega-3 per serving | | | | eat more than two portions of oily fish a week. |
| of 100g (about a 4 oz.) are: | | | | Mothers who consume contaminated fish before |
| 1. Atlantic Mackerel - 2.45g | | | | becoming pregnant are said to have children who are |
| 2. Chinook Salmon - 2.09g | | | | slower to develop and learn yet the fact is, that high |
| 3. Pacific Sardines - 1.87g | | | | maternal seafood consumption of the type known to |
| 4. Atlantic Herring - 1.67g | | | | be contaminated with mercury, has been associated |
| 5. Tuna - 1.57g | | | | with fewer - not more - autistic markers in the |
| 6. European Anchovies - 1.44g | | | | offspring. With the bulk of messages about fish |
| White fish also contains omega-3 fish oils although at | | | | consumption focused on risk, the benefits may be |
| much lower levels than the ones mentioned above. | | | | lost to consumers. Yet no such warning is given to |
| There are many other benefits that can be obtained | | | | these vulnerable groups when contaminants such as |
| by eating fish. Fatty fish also contains Vitamin D and | | | | mercury are found in high fructose corn syrup |
| selenium. One scientific study suggest that the | | | | (HFCS), which is used as a sugar additive in a wide |
| beneficial effects of omega-3 oils particularly on | | | | variety of the processed foods we consume. |
| stroke and CHD, may be due to vitamin D or | | | | One study done in 2006, gives a good overview of |
| selenium, or additional components of fish other than | | | | the levels of omega-3 oils and contaminants in |
| omega-3 oils. This study does however, pool the | | | | commonly consumed fish, shellfish, and other foods |
| omega 3 oils obtained from vegetable origin | | | | (see Table 2). From this it is obvious that some |
| (α-linolenic acid) and fish omega-3 oils when | | | | fishes have more contaminants than others and this |
| doing the comparison between omega-3 with vitamin | | | | will also depend not just on the type of fish but also |
| D or selenium and this may have distorted the final | | | | where it has been raised or farmed. Some fish and |
| analysis. | | | | vegetable oils have more omega-6 (Linoleic acid) |
| Vitamin D has gained increasing recognition for | | | | polyunsaturated fatty acid. For instance, tilapia has a |
| reducing the risk of many chronic and infectious | | | | much higher content of omega-6 than omega-3 oils |
| diseases and mortality rates especially from | | | | yet most of us will think we are getting a good |
| epidemiological studies. Vitamin D inadequacy is | | | | source of omega-3 by eating tilapia! Although |
| common worldwide and classically causes | | | | omega-6 oils are required by the body, current |
| osteomalacia and rickets. More recently, the | | | | evidences suggest that it is the ratio of omega-3 to |
| contribution of low vitamin D status to increased falls | | | | omega-6 is that is crucial in preventing disease and |
| and fracture risk has become appreciated. Now, | | | | cancer. |
| Vitamin D is the current wonder compound. One | | | | Our modern day diet consists of too much of the |
| recent study indicates that high vitamin D status | | | | omega-6 oils even in foods that we may think are |
| appears to correlate to reduced risk of several | | | | natural. Take something as simple as eggs: feeding |
| cancers, including colorectal cancer. Recently, interest | | | | hen with one type of feed may produce eggs with a |
| has also extended to studying vitamin D's benefits | | | | particular ratio of omega-6: omega-3. Supermarket |
| for the brain. Low vitamin D status is being potentially | | | | eggs have a 20:1 ratio whereas range-fed eggs have |
| associated with a multitude of conditions (including | | | | a 1.5:1 ratio of omega-6: omega-3. When you see |
| Alzheimer disease, osteoarthritis, multiple sclerosis, | | | | eggs or any other products on supermarket shelves |
| and hypertension) and higher overall mortality. | | | | that state these have been enriched with omega-3, |
| Consuming fish is inversely correlated with Alzheimer's | | | | all it means is that there is slightly more omega-3 in |
| disease (AD) prevalence and a 2010 review also | | | | these products but there is still a high amount of |
| describes how Vitamin D deficiency may be a cause | | | | omega-6! Meat from grass-fed animals has two to |
| for autism. | | | | four times more omega-3 oils than meat from grain- |
| The two major naturally relevant forms of Vitamin D | | | | fed animals. One recent publication, showed that a |
| are vitamin D2 (ergocalciferol) and vitamin D3 | | | | 35% fat diet with an omega-6: omega-3 ratio of 28:1 |
| (cholecalciferol). Synthetic Vitamin D is D2 yet these | | | | caused obesity that progressively increased over |
| supplements do not necessarily work in reducing | | | | four generations of mice. Although most studies like |
| deficiency. It is the naturally occurring vitamin D that | | | | this have their own flaws, they nevertheless |
| is by far the most widely used form for correcting | | | | together suggest that an imbalance of these PUFA is |
| vitamin D deficiency. Research also indicates that | | | | capable of causing obesity in mice that worsens over |
| omega-3 fats may also be better absorbed from | | | | several generations. |
| food than supplements. Selenium is also one of those | | | | The half-life of omega-6 in fat tissue is about two |
| minerals that cannot be added to our food once it | | | | years, so reducing it is a long-term prospect. Our |
| has been processed. Taking these into consideration, | | | | advice has been to eat fish to obtain the essential |
| it would seem that the best way of obtaining omega | | | | omega-3 oils. Also, consider choosing a wider variety |
| 3, vitamin D and selenium might be from the natural | | | | as this will not only help maintain a balanced omega-6: |
| source especially from fish. This statement is further | | | | omega-3 ratio but will help reduce the environmental |
| strengthened by a recent study where low intake of | | | | impact. Young children are advised to avoid some |
| fish, polyunsaturated oils (PUFA) and vitamin D | | | | types of fish, such as shark, swordfish, king |
| deficiency has been suggested to play a role in the | | | | mackerel, or tilefish, and to eat up to 12 ounces per |
| development of schizophrenia. This was a huge study | | | | week of fish and shellfish that are lower in mercury, |
| with more than 33,000 subjects (although it was | | | | such as shrimp, canned light tuna, salmon, pollock, and |
| self-assessment questionnaire), so the outcomes are | | | | catfish. |
| more relevant. Fish is necessary as part of our | | | | The list below shows the amount of various types of |
| healthy diet, there is no doubt about that. | | | | fish that a woman who is pregnant or planning to |
| Government policy documents and health professional | | | | become pregnant can safely eat. Small children should |
| organizations recommend we eat more fish. We | | | | reduce portion sizes. |
| should be aiming to eat at least two portions and up | | | | Fish that contains least mercury (less than 0.09 parts |
| to four portions of fish per week, one of which | | | | per million) are: |
| should be oily. Conversely, there are many of us who | | | | Anchovies |
| worry about what else we may be eating with our | | | | Herring |
| fish. It is true that most fish will contain some | | | | Mackerel (North Atlantic, Chub) |
| mercury or PCBs or both or other environmental | | | | Salmon (Fresh wild) |
| contaminants, just like any of the other food we | | | | Sardines |
| consume. These contaminants build up in the fatty | | | | Depending on where you live, you can enjoy at least |
| tissues of fish and other animals and by frequent | | | | one of these omega-3 rich fish at least 2 times a |
| consumption of this contaminated food they | | | | week. If you live in the Atlantic, the Atlantic Mackerel |
| accumulate in your body over time and may result in | | | | would be the best choice as it provides the highest |
| health problems, ranging from small, hard-to-detect | | | | omega-3 fish oil and the lowest mercury levels and |
| changes to birth defects and cancer. Environmental | | | | hardly any PCBs. Wild Alaskan Salmon has hardly any |
| contaminants such mercury, lead, arsenic, PCBs and | | | | mercury but has higher levels of PCBs. |
| dioxins, brominated flame retardants, arsenic, lead, | | | | Fish with high amount of mercury (0.3 to 0.49 parts |
| cadmium, and other organic and inorganic | | | | per million) are: |
| contaminants are inadvertently present in a wide | | | | Mackerel (Spanish, Gulf) |
| variety of our food. These environmental | | | | Tuna (Canned Albacore) |
| contaminants are discussed more in detail in our book | | | | Tuna (Yellowfin) |
| "Is Your Food Killing You?" | | | | Of these fish, eat three servings or less per month |
| Mercury is one of the main concerns of a | | | | If trying to avoid contaminants from fish, then avoid |
| contaminant found in fish. Mercury is a reactive heavy | | | | these fish: (mercury levels of more than 0.5 parts per |
| metal emitted from natural sources (volcanoes) and | | | | million) |
| human sources (coal-fired electric power plants, gold | | | | Mackerel (King) |
| mining, institutional boilers, chlorine production, and | | | | Tuna (Bigeye, Ahi)* |
| waste incineration). From the atmosphere, mercury | | | | Farmed salmon |
| cycles from rainwater into lakes and oceans, where it | | | | A more in-depth analysis of mercury and other |
| is converted by bacteria into methylmercury. | | | | contaminants in fish is available here. Also remember |
| Inorganic mercury is poorly absorbed following | | | | that cooking can alter the omega-3 content in your |
| ingestion, and elemental mercury does not readily | | | | fish depending on how which method you choose to |
| cross tissue barriers. In contrast, methylmercury is | | | | cook your fish. More about the cooking process is |
| readily absorbed and actively transported into tissues. | | | | covered in our book. |
| Fish therefore absorb methylmercury mostly from | | | | In conclusion, if you are worried about mercury and |
| their food, but also from the water as it passes over | | | | PCB or other contaminants, it is not just from the |
| their gills. Concentrations of methylmercury in aquatic | | | | fish source that you should be worried about. |
| species depend on levels of environmental | | | | Mercury (along with aluminium and residual |
| contamination and on the type of fish. Generally, | | | | formaldehyde, all of which are nasty compounds) can |
| larger, older predators (e.g., swordfish, shark) have | | | | be found in vaccines such as in tetanus and diphtheria |
| higher tissue concentrations, while smaller or younger, | | | | toxoids. In our article entitled "Environmental |
| shorter lived species (e.g., shellfish, salmon) have very | | | | exposures and Cancer risk", we show that |
| low concentrations. In addition, the large predatory | | | | environmental pollutions can be found in the foods |
| fish near the top of marine food chains are more | | | | we consume daily! Reduce the intake of these foods |
| likely to have high levels of mercury than fish lower in | | | | instead if you are worried about eating contaminated |
| marine food chains due to the process of | | | | foods! Gain the benefits of omega 3 from fish by |
| biomagnifications. Since methylmercury binds to | | | | eating the right kinds of fish and cooking it correctly. |