Omega-3 fatty acid
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–carbon
double 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 are:
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- and 22-carbon unsaturated
n−3 fatty acids 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.
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) 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.
Note that taking the 18 carbon α-linolenic acid has not been shown
to have the same cardiovascular benefits as DHA or EPA. Currently there
are many products on the market which claim to contain health promoting
'omega 3', but contain only α-linolenic acid (ALA), not EPA or DHA.
These products contain mainly higher plant oils and must be converted
by the body to create DHA and therefore considered less efficient. DHA
and EPA are made by microalgae that live in seawater. These are then
consumed by fish and accumulate to high levels in their internal
organs. If a person is concerned about mercury and oceanborne
contaminants in fish, DHA can be produced directly from microalgae as a
vegetarian source. People with certain circulatory problems, such as varicose veins, benefit from fish oil because it contains the EPA and DHA derived from microalgae. Fish oil stimulates blood circulation, increases the breakdown of fibrin, a compound involved in clot and scar formation, and additionally has been shown to reduce blood pressure.[3][4] There is strong scientific evidence that n−3 fatty acids reduce blood triglyceride levels[5][6][7][8] and regular intake reduces the risk of secondary and primary heart attack.[9][10][11][12]
Some benefits have been reported in conditions such as rheumatoid arthritis[13][14] and cardiac arrhythmias.[15][16][17]
There is preliminary evidence that n-3 fatty acids supplementation might be helpful in cases of depression[18][19] and anxiety.[20][21] Studies report highly significant improvement from n-3 fatty acids supplementation alone and in conjunction with medication.[22]
Some research suggests that fish oil intake may reduce the risk of ischemic and thrombotic stroke.[23][24][25]
However, very large amounts may actually increase the risk of
hemorrhagic stroke (see below). Lower amounts are not related to this
risk,[25] 3 grams of total EPA/DHA daily are considered safe with no increased risk of bleeding involved[26]
and many studies used substantially higher doses without major side
effects (for example: 4.4 grams EPA/2.2 grams DHA in 2003 study).[18]
Some research suggests that fish oil intake may reduce the risk of ischemic and thrombotic stroke.[23][24][25] However, very large amounts may actually increase the risk of hemorrhagic stroke (see below). Lower amounts are not related to this risk,[25] 3 grams of total EPA/DHA daily are considered safe with no increased risk of bleeding involved[26] and many studies used substantially higher doses without major side effects (for example: 4.4 grams EPA/2.2 grams DHA in 2003 study).
