|
|
|
DHA :
Linoleic acid (LA) is an omega - 6 fatty acid and alpha-linolenic acid (ALA) is an omega-3 fatty acid are essential fatty acids for normal growth and development. These fatty acids cannot be synthesized in the human body and must be obtained from the diet. These fatty acids are converted into very long chain polyunsaturated fatty acids (LC-PUFAs) through a series of desaturases and elongases. (1) LA is converted to docosahexaenoic acid (DHA) in the body, however rate of conversion varies from 0.2% and 21%.(2) The PUFA are important constituents of phospholipids. Phospholipids has been shown to be associated with normal growth and development, as well as in the outcome of chronic diseases such as coronary heart disease (CHD), hypertension, cancer, arthritis, allergies and other autoimmune diseases, since both omega-6 and omega-3 PUFAs are processed to powerful promoters of eicosanoids such as prostaglandins and leukotrienes. (3)
There is mounting literature to indicate that DHA may be of considerable benefit in the development of, retarding the progress of, or helping manage a number of chronic disorders especially cardiovascular disease/outcomes and associated risk factors. (4)
Action of DHA (5):
(1) |
|
Decreased production of prostaglandin E2 (PGE2) metabolites |
(2) |
|
Decrease in thromboxane A2, a potent platelet aggregator and vasoconstrictor |
(3) |
|
Decrease in leukotriene B4 formation, an inducer of inflammation and a powerful inducer of leukocyte chemotaxis and adherence |
(4) |
|
Increase in thromboxane A3, a weak platelet aggregator and a weak vasoconstrictor |
(5) |
|
Increase in prostacyclin PGI3, leading to an overall increase in total prostacyclin by increasing PGI3 without a decrease in PGI2. Both PGI2 and PGI3 are active vasodilators and inhibitors of platelet aggregation; and |
(6) |
|
Increase in leukotriene B5, a weak inducer of inflammation and a weak chemotactic agent |
Thus, DHA in high doses lowers cholesterol and has anti-thrombotic and anti-inflammatory properties. (1)
|
|
DHA and Cardiovascular Effects: |
|
|
DHA and cardiovascular effects: In 3 large controlled trials of 32,000 participants randomized to receive omega-3 fatty acid supplements containing docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), results showed reductions in cardiovascular events of 19% to 45%. These findings suggest that intake of omega-3 fatty acids, whether from dietary sources or fish oil supplements, should be increased, especially in those with or at risk for coronary artery disease (6). The American Heart Association (AHA) has endorsed the use of omega-3 fatty acids for secondary prevention of cardiovascular (CV) events in people with documented coronary artery disease (CAD). The recommendation calls for approximately 1 g/d of a mixture of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). (7) The Food and Drug Administration (FDA) has approved an omega-3 fatty acid ethyl ester formulation, at a dosage of 4.0 g/d, for the treatment of very high triglyceride levels. (6)
|
|
|
DHA and mental health: Observational studies support a direct association between poor n-3 fatty acid status and increased risk of maternal depression and childhood behavioral disorders such as attention-deficit hyperactivity disorder (ADHD)(8) and there may be a role of increasing DHA intake in these individuals. Results in young children suggest that neurodevelopment and cognitive abilities are also enhanced by early provision of omega-3 PUFA through breast milk or DHA-fortified foods. Similarly, prospective cohort studies have shown that increased fish consumption and higher omega-3 PUFA in blood lipid sub-fractions are associated with decreased risk of dementia in older people. (9)
|
|
|
DHA in Chronic Pediatric Disorders: Low plasma and/or red blood cell DHA content has been documented in infants and children with fetal alcohol syndrome, attention deficit hyperactivity disorder, cystic fibrosis, phenylketonuria, unipolar depression, aggressive hostility, and congenital metabolic disorders, particularly adrenoleukodystrophy. (10)
Other effects of DHA: Usefulness of DHA has already been established for visual performance. However it has been found that dietary DHA Omega-3 may protect against gum disease, act as anti-inflammatory agent for discogenic pain. Risk for colorectal cancer was 12% lower in those with adequate fish intake (fish being a good source of essential fatty acids). (4)
Conclusion: Protective effect of DHA is most likely to be due to the fundamental properties of docosahexaenoic acid in cell function. Evidence shows that omega-3 PUFA play important roles in heart health, brain health, child and infant development, inflammation and other functions. Unfortunately the typical westernization of diet and Indian vegetarian diet does not supply enough EPA and DHA, which may contribute to increased risk of chronic diseases. (11)
References:
1. |
Simopoulos AP. Genetic variants in the metabolism of omega-6 and omega-3 fatty acids: their role in the determination of nutritional requirements and chronic disease risk. Exp Biol Med (Maywood). 2010; 235: 785-795 |
2. |
BurdgeG. Alpha-linolenic acid metabolism in men and women: nutritional and biological implications. Current Opin Clin Nutri Metab Care 2004;7:137-144 |
3. |
SimopoulosAP. The importance of the omega-6/omega-3 fatty acid ratio in cardiovascular disease and other chronic diseases. Exp Biol Med (Maywood) 2008; 233: 674-688 |
4. |
|
5. |
LewisRA, LeeTH, AustenKF. Effects of omega-3 fatty acids on the generation of products of the 5-lipoxygenase pathway. In: SimopoulosAP, KiferRR, MartinRE, eds. Health Effects of Polyunsaturated Fatty Acids in Seafoods. Orlando: Academic Press, 1986:227-238 |
6. |
Lee JH, O'Keefe JH, Lavie CJ, Marchioli R, Harris WS. Omega-3 fatty acids for cardioprotection. Mayo Clin Proc. 2008 Mar;83(3):324-32 |
7. |
Kris-Etherton PM, Harris WS, Appel LJ, American Heart Association Nutrition Committee. Fish consumption, fish oil, omega-3 fatty acids, and cardiovascular disease [published correction appears in Circulation. 2003; 107: 512. |
8. |
Ramakrishnan U, Imhoff-Kunsch B, DiGirolamo AM. Role of docosahexaenoic acid in maternal and child mental health. Am J Clin Nutr. 2009; 89: 958S-962S |
9. |
Dangour AD, Uauy R. N-3 long-chain polyunsaturated fatty acids for optimal function during brain development and ageing. Asia Pac J Clin Nutr. 2008; 17 Suppl 1:185-188 |
10. |
Long-chain Polyunsaturated Fatty Acids in Chronic Childhood Disorders: Possible Additions to Special Products. Available at url: http://www.ifm.net/industry/lpufa.htm. Accessed on 30th August 2010 |
11. |
|
|
| |
|
|
|
|
|
