OMEGA 3

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n−3 fatty acids (popularly referred to as ω−3 fatty acids or omega-3 fatty acids) are a family of unsaturated fatty acids that have in common a final carbon–carbondouble bond in the n−3 position; that is, the third bond from the methyl end of the fatty acid.

Important nutritionally essential n−3 fatty acids include α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), all of which are polyunsaturated. The human body cannot synthesize n−3 fatty acids de novo, but it can form 20-carbon unsaturated n−3 fatty acids (like EPA) and 22-carbon unsaturatedn−3 fatty acids (like DHA) from the eighteen-carbon n−3 fatty acid α-linolenic acid. These conversions occur competitively with n−6 fatty acids, which are essential closely related chemical analogues that are derived from linoleic acid. Both the n−3 α-linolenic acid and n−6 linoleic acid are essential nutrients which must be obtained from food. Synthesis of the longer n−3 fatty acids from linolenic acid within the body is competitively slowed by the n−6 analogues. Thus accumulation of long-chain n−3 fatty acids in tissues is more effective when they are obtained directly from food or when competing amounts of n−6 analogs do not greatly exceed the amounts of n−3.^{[citation needed]}

[edit]History

Although omega-3 fatty acids have been known as essential to normal growth and health since the 1930s, awareness of their health benefits has dramatically increased in the past few years.^[1] New versions of ethyl esterized omega-3 fatty acids, such as E-EPA and combinations of E-EPA and E-DHA, have drawn attention as highly purified and more effective products than the traditional ones. In the United States, these novel versions are often sold as prescription medications, such as Lovaza. In the European Union, they are available as dietary supplements.

The health benefits of the long-chain omega-3 fatty acids — DHA and EPA omega-3 — are the best known. These benefits were discovered in the 1970s by researchers studying the Greenland Inuit Tribe. The Greenland Inuit people consumed large amounts of fat from seafood, but displayed virtually no cardiovascular disease. The high level of omega-3 fatty acids consumed by the Eskimos reduced triglycerides, heart rate, blood pressure, and atherosclerosis.^{[citation needed]}

On September 8, 2004, the U.S. Food and Drug Administration gave "qualified health claim" status to EPA and DHA n−3 fatty acids, stating that "supportive but not conclusive research shows that consumption of EPA and DHA [n−3] fatty acids may reduce the risk of coronary heart disease."^[2] This updated and modified their health risk advice letter of 2001 (see below). Currently, regulatory agencies do not accept that there is sufficient evidence for any of the other suggested benefits of DHA and EPA other than for cardiovascular health, and further claims should be treated with caution.

The Canadian Government has recognized the importance of DHA omega-3 and permits the following biological role claim for DHA: "DHA, an omega-3 fatty acid, supports the normal development of the brain, eyes and nerves." ^[3]

[edit]Chemistry

Chemical structure of alpha-linolenic acid (ALA), an essential n−3 fatty acid, (18:3Δ9c,12c,15c, which means a chain of 18 carbons with 3 double bonds on carbons numbered 9, 12 and 15). Although chemists count from the carbonyl carbon (Blue Numbering), physiologists count from the n (ω) carbon (red numbering). Note that from the n end (diagram right), the first double bond appears as the third carbon-carbon bond (line segment), hence the name "n−3". This is explained by the fact that the nend is almost never changed during physiologic transformations in the human body, as it is more stable energetically, and other carbohydrates compounds can be synthesized from the other carbonyl end, for example in glycerides, or from double bonds in the middle of the chain.

Chemical structure of eicosapentaenoic acid (EPA).

Chemical structure of docosahexaenoic acid (DHA).

The term n−3 (also called ω−3 or omega-3) signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (n) of the carbon chain.

n−3 fatty acids which are important in human nutrition are: α-linolenic acid (18:3, n−3; ALA), eicosapentaenoic acid (20:5, n−3; EPA), and docosahexaenoic acid (22:6, n−3; 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; in other words, the two hydrogen atoms are on the same side of the double bond.

Most naturally-produced fatty acids (created or transformed in animalia or plant cells with an even number of carbon in chains) are incis-configuration where they are more easily transformable. The trans-configuration results in much more stable chains that are very difficult to further break or transform, forming longer chains that aggregate in tissues and lacking the necessary hydrophilic properties. This trans-configuration can be the result of the transformation in alkaline solutions, or of the action of some bacterias that are shortening the carbonic chains. Natural transforms in plant or animal cells more rarely affect the last n−3 group itself. However, n−3 compounds are still more fragile than n−6 because the last double bond is geometrically and electrically more exposed, notably in the natural cis configuration.

[edit]List of n−3 fatty acids

This table lists several different names for the most common n−3 fatty acids found in nature.

[edit]Biological significance

The biological effects of the n−3 are largely mediated by their interactions with the n−6 fatty acids; see Essential fatty acid interactions for detail.

A 1992 article by biochemist William E.M. Lands^[4] provides an overview of the research into n−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 n−3 in the diet (~1% of total calories) enabled normal growth, and increasing the amount had little to no additional effect on growth.

Likewise, researchers found that n−6 fatty acids (such as γ-linolenic acid and arachidonic acid) play a similar role in normal growth. However, they also found that n−6 was "better" at supporting