Omega-3 fatty acid
2007 Schools Wikipedia Selection. Related subjects: Health and medicine
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Omega-3 fatty acids are polyunsaturated fatty acids which have a C=C double bond in the ω-3 position. (See Nomenclature for terms and discussion of ω (omega) nomenclature.)
Important omega-3 fatty acids in human nutrition are: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). For a more complete list see List of omega-3 fatty acids. The human body cannot synthesize omega-3 fatty acids from scratch, but can synthesize all the other necessary omega-3 fatty acids from the omega-3 fatty acid Alpha-linolenic acid. Therefore Alpha-linolenic acid is an Essential nutrient which must be obtained from food, and the other omega-3 fatty acids which can be either synthesized from it within the body or obtained from food are sometimes also referred to as essential nutrients.
Chemistry
The term omega-3 (aka "n-3", "ω-3") signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (ω) of the carbon chain.
Omega-3 fatty acids which are important in human nutrition are: alpha-linolenic acid (18:3, ALA), eicosapentaenoic acid (20:5, EPA), and docosahexaenoic acid (22:6, DHA). These three polyunsaturates have either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon atoms, respectively. All double bonds are in the cis-configuration, i.e. the two hydrogen atoms are on the same side of the double bond.
Biological significance
- The biological effects of the ω-3 fatty acids are largely mediated by their interactions with the ω-6 fatty acids, see Essential fatty acid interactions for detail.
A 1992 paper by biochemist William E.M. Lands provides an overview of the research into omega-3 fatty acids, and is the basis of this section.
The 'essential' fatty acids were given their name when researchers found that they were essential to normal growth in young children and animals. (Note that the modern definition of ' essential' is more strict.) A small amount of omega-3 in the diet (~1% of total calories) enabled normal growth, and increasing the amount had little to no additional benefit.
Likewise, researchers found that omega-6 fatty acids (such as γ(gamma)-linolenic acid and arachidonic acid) play a similar role in normal growth. However they also found that omega-6 is "better" at supporting dermal integrity, renal function, and parturition. This led researchers to concentrate study on omega-6, and it is only in recent decades that omega-3 has become of interest.
In 1963 it was discovered that the omega-6 arachidonic acid is converted by the body into pro-inflammatory agents called prostaglandins,. By 1979 more of what are now known as eicosanoids were discovered: thromboxanes, prostacyclins and the leukotrienes. The eicosanoids, which have important biological functions, typically have a short active lifetime in the body, starting with synthesis from fatty acids and ending with metabolism by enzymes. However if the rate of synthesis exceeds the rate of metabolism, the excess eicosanoids may have deleterious effects. Researchers found that omega-3 is also converted into eicosanoids, but at a much slower rate. Eicosanoids made from omega-3 fats often have opposing functions to those made from omega-6 fats (ie, anti-inflammatory rather than inflammatory). If both omega-3 and omega-6 are present, they will "compete" to be transformed, so the ratio of omega-3:omega-6 directly affects the type of eicosanoids that are produced.
This competition was recognized as important when it was found that thromboxane is a factor in the clumping of platelets, which leads to thrombosis. The leukotrienes were similarly found to be important in immune/inflammatory-system response, and therefore relevant to arthritis, lupus, and asthma. These discoveries led to greater interest in finding ways to control the synthesis of omega-6 eicosanoids. The simplest way is by consuming more omega-3 and less omega-6 fatty acids.
Cardiovascular health benefits
On September 8, 2004, the U.S. Food and Drug Administration gave "qualified health claim" status to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) omega-3 fatty acids, stating that "supportive but not conclusive research shows that consumption of EPA and DHA omega-3 fatty acids may reduce the risk of coronary heart disease."
A 2006 report in the Journal of the American Medical Association concluded that their review of literature covering cohorts from many countries with a wide variety of demographic characteristics failed to demonstrate a link between omega-3 fatty acids and cancer prevention. This is similar to the findings of a review by the British Medical Journal of studies up to February 2002 that failed to find clear effects of long and shorter chain omega-3 fats on total mortality, combined cardiovascular events and cancer.
In April 2006, a team led by Lee Hooper at the University of East Anglia in Norwich, UK, published a review of almost 100 separate studies into omega-3 fatty acids, found in abundance in oily fish. It concluded that they do not have a significant protective effect against cardiovascular disease.
The above stands in stark contrast with two different reviews also performed in 2006 by the American Journal of Clinical Nutrition and a second JAMA review that both indicated decreases in total mortality and cardiovascular incidents (i.e. myocardial infarctions) associated with the regular consumption of fish and fish oil supplements. Of particular importance is that no or very few complications were documented.
Research in 2005-06 has suggested that the in-vitro anti-inflammatory activity of omega-3 acids translates into clinical benefits. Cohorts of neck pain patients and of rheumatoid arthritis sufferers have demonstrated benefits comparable to those receiving standard NSAIDs.
Those who follow a Mediterranean-style diet tend to have higher HDL ("good") cholesterol levels. Similar to those who follow a Mediterranean diet, Arctic-dwelling Inuit - who consume high amounts of omega-3 fatty acids from fatty fish - also tend to have increased HDL cholesterol and decreased triglycerides (fatty material that circulates in the blood). In addition, fish oil supplements containing EPA and DHA have been shown to reduce LDL ("bad") cholesterol and triglycerides. Finally, walnuts (which are rich in ALA) have been shown to lower total cholesterol and triglycerides in people with high cholesterol.
Omega-3 fatty acids and Autism
According to an internet survey approximately 30% of parents use omega-3 supplements as a therapy for autistic children. There are currently only a few studies on the effectiveness of essential fatty acid supplementation as a treatment of autism and none of these have been well-controlled. Bell and colleagues reported that parents of 18 autistic children who had been supplemented with fish oil for six months described improvements in overall health, cognition, sleep patterns, social interaction, and eye contact. Another case report found that an autistic child given 540 mg of EPA per day over a four week period experienced a complete elimination of his previous anxiety about everyday events as reported by his parents and clinician.
Health risks
In a letter dated October 31, 2000 entitled Letter Regarding Dietary Supplement Health Claim for omega-3 Fatty Acids and Coronary Heart Disease, the U. S. Food and Drug Administration Centre for Food Safety and Applied Nutrition, Office of Nutritional Products, Labeling, and Dietary Supplements noted that the known or suspected risks of omega-3 fatty acids may include:
- Increased bleeding can occur if overused (normally over 3 grams per day)
- The possibility of hemorrhagic stroke
- Oxidation of omega-3 fatty acids forming biologically active oxidation products
- Increased levels of low density lipoproteins (LDL) cholesterol or apoproteins associated with LDL cholesterol among diabetics and hyperlipidemics
- Reduced glycemic control among diabetics
- Suppression of immune and inflammation responses, and consequently, to decreased resistance to infections and increased susceptibility to opportunistic bacteria
The following risks have been attributed to the FDA but are not mentioned in the above letter:
- A significant potential risk is the possibility of vitamin poisoning from taking large doses of supplements which contain large quantities of vitamins (particularly vitamin A) in addition to omega-3 fatty acids. For this reason, the primary source of omega-3, if taken as a supplement, should be from fish body oil and not from a fish liver based oil.
Warning for persons with CHF
Persons with congestive heart failure, chronic recurrent angina or evidence that their heart is receiving insufficient blood flow are advised to talk to their doctor before taking omega-3 fatty acids. It may be prudent for such persons to avoid taking omega-3 fatty acids or eating foods that contain them.
In a congestive heart failure, cells that are only barely receiving enough blood flow become hyperexcitable. This, in turn, can lead to an increased risk of irregular heartbeats, which, in turn, can cause sudden cardiac death. Omega-3 fatty acids stabilize the rhythm of the heart by effectively removing these hyper-excitable cells from functioning, thereby reducing the likelihood of irregular heartbeats and sudden cardiac death. For most people, this is a very good thing and accounts for most of the large reduction in the likelihood of sudden cardiac death. However, for persons with congestive heart failure, the heart is barely pumping blood well enough to keep them alive. Omega-3 fatty acids may eliminate enough of these pumping cells that the heart is no longer able to pump sufficient blood to live, causing an increased risk of cardiac death.
Research frontiers
Psychological disorders
Omega-3s are definitively known to have membrane-enhancing capabilities in brain cells. One medical explanation is that omega-3s play a role in the fortification of the myelin sheaths. Not coincidentally, omega-3 fatty acids comprise approximately eight percent of the average human brain according to the late Dr. David Horrobin, a pioneer in fatty acid research. Ralph Holman of the University of Minnesota, another major researcher in studying essential fatty acids, who gave it the name, surmised how omega-3 components are analogous to the human brain by stating that "DHA is structure, EPA is function."
A benefit of Omega-3s is helping the brain to repair damage by promoting neuronal growth. In a six-month study involving people with schizophrenia and Huntington's disease who were treated with EPA or a placebo, the placebo group had clearly lost cerebral tissue, while the patients given the supplements had a significant increase of grey and white matter.
Consequently, the past decade of omega-3 fatty acid research has procured some Western interest in omega-3s as being a legitimate 'brain food.' Still, recent claims that one's intelligence quotient, psychological tests measuring certain cognitive skills, including numerical and verbal reasoning skills, are increased on account of omega-3s consumed by pregnant mothers remain unreliable and controversial. An even more significant focus of research, however, lies in the role of omega-3s as a non-prescription treatment for certain psychiatric and mental diagnoses and has become a topic of much research and speculation.
In 1999, Andrew L. Stoll, MD and his colleagues at Harvard University conducted a small double-blind placebo-controlled study in thirty patients diagnosed with Bipolar disorder. Over the course of nine months, he gave 15 subjects capsules containing olive oil, and another 15 subjects capsules containing nine grams of pharmaceutical-quality EPA and DHA. In doing, so he was able to make the general distinction between the placebo group failing to improve while the Omega-3 group experienced a noticeable degree of recovery. Though Stoll believes that the 1999 experiment was not as optimal as it could have been and has accordingly pursued further research, the foundation has been laid for more researchers to explore the theoretical association between absorbed omega-3s and signal transduction inhibition in the brain. Andrew Stoll MD also owns a company called Omegabrite that sells an Omega 3 oil supplement.
Should enough research that is currently underway come to confirm the legitimacy of this association, then a debate and reassessment will of course be necessitated between Omega-3s and such prescription bipolar treatments as lithium, or brand Eskalith and various FDA approved and "off label" use pharmacologic agents. Some physicians and psychiatric specialists in the United States do allow willing bipolar patients to use Omega-3 supplements as complementary or conditional treatments. Omega-3s, unlike many psychopharmacologic [medication] treatments, are less expensive and do not commonly induce such side effects as diarrhea, drowsiness, and fatigue. At present, more research is needed before recommending that people with bipolar disorder or other mental illnesses take Omega-3 supplements.
The omega-6 to omega-3 ratio
Clinical studies indicate that the ingested ratio of omega-6 to omega-3 (especially Linoleic vs Alpha Linolenic) fatty acids are important to maintaining cardiovascular health.
Both omega-3 and omega-6 fatty acids are essential, i.e. humans must consume them in the diet. Omega-3 and omega-6 compete for the same metabolic enzymes, thus the omega-6:omega-3 ratio will significantly influence the ratio of the ensuing eicosanoids (hormones), (e.g. prostaglandins, leukotrienes, thromboxanes etc.), and will alter the body's metabolic function. Metabolites of omega-6 are significantly more inflammatory (esp. arachidonic acid) than those of omega-3. This necessitates that omega-3 and omega-6 be consumed in a balanced proportion; the ideal ratio of omega-6:omega-3 being from 3:1 to 5:1. Studies suggest that the evolutionary human diet, rich in seafood, nuts and other sources of omega-3, may have provided such a ratio.
Simopoulos, et al recommend daily intakes of three omega-3 forms: 650 mg of EPA and DHA, and 2.22 g of ALA, and one omega-6 form: 4.44 g of LA. This translates to a 3:2 omega-6 to omega-3 ratio. (i.e. 1.5:1)
Typical Western diets provide ratios of between 10:1 and 30:1 - i.e., dramatically skewed toward omega-6. Here are the ratios of omega-3 to omega-6 fatty acids in some common oils: sunflower (no omega-3), cottonseed (almost no omega-3), canola 2:1, peanut (no omega-3), grapeseed oil (almost no omega-3) and corn oil 46 to 1 ratio of omega-6s to omega-3s.