Omega-3 fatty acids are polyunsaturated fatty acids found in certain fish tissues, and in vegetable sources such as flax seeds, walnuts, and canola oil.

Omega-3 fatty acids are classed as essential fatty acids. These fatty acids were originally designated as "Vitamin F", until it was realized that they must be classified with the fats.

The term "omega-3" signifies that the first double bond in the carbon backbone of the fatty acid, counting from the end opposite the acid group, occurs in the third carbon-carbon bond. This way of counting was introduced by physiologists. Chemists would normally count the position of the double bond from the acid end position (the alpha positions). However by counting from the other end, physiologists revealed the similarity between fatty acids of diverse length.

Like all polyunsaturated fatty acids, the omega-3 fatty acids have minimum 2 and maximum 6 double bonds in a carbon chain that ranges from 18 until 22 carbon atoms.

In natural conditions, the double bonds are in the cis-conformation, with the two hydrogen atoms at the same side of the double bond. This characteristic, along with the fact that every double bond is separated by a methyl group, explains the 3D-structure and the properties of omega-3 and omega-6 fatty acids as well as those of the phospholipids that contain them. With every additional cis bond, the carbon chain will change direction, so that the long omega-3 and omega-6 chain structure is not one long straight chain, but a twisted molecule. This simple difference explains a host of biological phenomena in structures that are rich in polyunsaturated fatty acids, especially the lipid bilayer of the cell membrane.

Common omega-3 fatty acids in the body are (alpha)linolenic acid (18:3), eicosapentaenoic acid (20:5), docosahexaenoic acid (22:6). Gamma-linolenic acid is an omega-6 fatty acid.

It has been conjectured that the diet in the Human Environment of Evolutionary Adaptedness may have been rich in seafood, nuts and other sources of vegetal omega-3, and that modern diets are deficient in the ratio of omega-3 to omega-6 fatty acids, perhaps leading to a number of modern illnesses.

Arachidonic Acid, an omega-6 fatty acid (C20:4, n-6), is one of the most important precursors of anti-inflammatory prostaglandins. These precursors are jointly referred to as eicosanoids since they have 20 carbon atoms (eicosa is Greek for 20). Since the metabolism of omega-3 and omega-6 fatty acids shares common enzymes (elongase and desaturase enzymes), its is widely accepted that both types of polyunsaturated fatty acids behave as competitive substrates. However, the desaturation of omega-3 fatty acids leads to less inflammatory eicosanoids than arachidonic acid. It is also likely that omega-3 fatty acids such as eicosapentaenoic acid have very specific biological activities. EPA supplementation inhibits or attenuates the pro-inflammatory cascade that follows on the enzymatic release of free arachidonic acid from the cell membrane. In this respect, some researchers have uncovered interesting parallels between the biological effect of aspirine, NSAIDs (non-steroidal anti-inflammatory drugs) and fish oil.

The scientific and commercial attention about the effect of omega-3 fats on inflammation and inflammatory signals, has really exploded since the 1990s.

Possible benefits of omega-3 fatty acids

A number of remarkable benefits have been attributed to omega-3 fatty acids in recent years. However, these are so far provisional results, and cannot yet be regarded as fact until they have been confirmed by further studies.

• There are preliminary reports that supplementing the diet with large doses of omega-3 oils may act as a mood stabilizer, opening the possibility of their use as a treatment for depression and bipolar disorder. However, the reports relating to this state that care must be taken to avoid overdose, and more research is needed.
• Lower doses have also been reported as having possible beneficial cardiovascular effects,.
• There are also initial reports that omega-3 fatty acids may lower the risk of dementia in old age.

Known and suspected risks of omega-3 fatty acids

In its letter entitled Letter Regarding Dietary Supplement Health Claim for Omega-3 Fatty Acids and Coronary Heart Disease the U. S. Food and Drug Administration Center 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 times,
• 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

In addition, another potential risk is the possibility of vitamin poisoning from taking large doses of supplements which contain significant amounts of vitamins in addition to omega-3 fatty acids.

For these reasons, the FDA recommends that total dietary intake of omega-3 fatty acids be limited to 3g/day, of which no more than 2g/day should come from nutritional supplements. [1] (http://www.fda.gov/bbs/topics/news/2004/NEW01115.html) However, many nutritionists recommend more than this, pointing out that the studies used by the FDA only indirectly show that high doses of omega-3 fatty acids are harmful.

References

• Andrew L. Stoll et al. Omega 3 Fatty Acids in Bipolar Disorder - A Preliminary Double-blind, Placebo-Controlled Trial (http://archpsyc.ama-assn.org/cgi/content/short/56/5/407)
• "FDA ANNOUNCES DECISION ON ANOTHER HEALTH CLAIM FOR DIETARY SUPPLEMENTS" (http://www.fda.gov/bbs/topics/ANSWERS/ANS01050.html)
• U. S. Food and Drug Administration Center for Food Safety and Applied Nutrition, Office of Nutritional Products, Labeling, and Dietary Supplements: Letter Regarding Dietary Supplement Health Claim for Omega-3 Fatty Acids and Coronary Heart Disease (Docket No. 91N-0103)
• BBC News story: Fish 'lowers dementia risk' (http://news.bbc.co.uk/1/hi/health/2356665.stm)

See also

• Omega-6 fatty acid

External links

• New Findings About Omega-3 Fatty Acids and Depression (http://weeksmd.com/articles/psychiatry/depomega.php3)
• The A-Z`s of Omega 3`s (http://www.bipolarchild.com/newsletters/0501.html)