New insights into DHA
Sue McGarrigle ND DipION CNHC mBANT
For centuries, fishing communities all over the world have used fish oil for various purposes and it has gained wide acceptance for its health benefits. It has been estimated that the ratio of omega 6 to omega 3 fatty acids in the diet of early humans was 1:1; however we now know this all-important ratio has altered leading to an overwhelming increase in omega 6 in our current diets.
The need for arachidonic acid, (ARA) which is utilized for eicosanoid synthesis and is a constituent of membrane phospholipids involved in signal transduction, is the main reason why the omega 6 class of Polyunsaturated Fatty Acids (PUFAs) are essential but ARA’s involvement is in the metabolism of the highly inflammatory series 2 prostaglandins. Professor Michael Crawford, Director of the Institute of Brain Chemistry and Human Nutrition, a leading expert in Omega 3’s is convinced that the current ratio of 10:1 omega 6 to omega 3 in the diet is a major cause of many of the ‘diseases of civilisation’ and the cause of most inflammatory disease.
Over the years there has been extensive coverage in omega 3 research of the role of eicosapentaenoic acid (EPA) particularly with respect to inflammatory response. By implication, this has tended to downplay the essential role of docosahexaenoic acid (DHA). It is not the intention of this article to dismiss EPA but simply to redress the balance of understanding between DHA and EPA by explaining the functional essentiality of DHA. Although EPA also is a substrate for eicosanoid synthesis, DHA is an essential fatty acid universally needed in neurological tissues, for vascular tissue and is required for the maintenance of the central nervous system, the development of the brain and for visual function.
However DHA and its metabolites have a number of newly recognized multifunctional roles to play in other vital biochemical functions beyond that of simply being the major structural component in many biological membranes. DHA may have an integral role in modulating many vital intra-cellular activities. DHA plays an important role within the immune system influencing the activity of adhesion proteins on the lipid membrane environment, communication between leukocytes and the body, and the regulation of smooth muscle contraction. As an essential omega 3 constituent, research is revealing that DHA provides protection in reducing the hazards of immune-suppression.
EPA is physiologically important but at high levels of supplementation may exert a competitive inhibitory effect upon DHA metabolism in certain individuals. This is a factor that has perhaps only become relevant as overall levels of Omega 3 supplementation have increased over the past decade. Very small amounts of DHA may be made in the body from Alpha-linolenic Acid (ALA), but the amount made can be low due to a number of factors such as a lack of the vitamins (B3, B6, C) and minerals (zinc, magnesium) necessary for conversion, lack of enzymes through competition and ageing, other nutritional factors and toxic influences. There is evidence that high carbohydrate diets slow down conversion, and diets higher in proteins enhance conversion.
Impaired liver function where DHA synthesis occurs, impaired metabolic pathways due to viral and bacterial infection/damage contribute to the conversion reduction/blockage. Most DHA comes from our diet and there are some individuals who are more efficient at converting ALA ultimately to DHA but the majority of Westerners are poor converters and people who follow a low fat, low fish diet often miss out on beneficial long chain PUFA’s. Fish are the major food source of EPA and DHA and all fish contain EPA and DHA; notwithstanding the issues involving contaminated fish which has influenced our choices, the quantities do vary among species and within a species according to environmental variables such as diet and whether fish are wild or farm-raised.
A practical way to significantly increase DHA levels is to take a supplement that delivers higher levels of DHA. Conversion from ALA to EPA to DHA is minimal when you consider the requirement during pregnancy for example. Hormones during pregnancy increase conversion, something that evolved out of necessity as DHA is vital for foetal brain development and immune health.
Tuna is a good source of preformed DHA with a higher ratio of DHA to EPA,
which is interesting as Tuna consumption by the Japanese is very high and they have population per head higher IQ's than us in the Western World. Research from Paediatrics 2011 reported that a sample of 1094 pregnant women in Mexico were assigned to daily supplementation of DHA capsules (400mg/day) or placebo capsules from 18 to 22 weeks gestation to childbirth.
Mothers completed a 15-day recall questionnaire on common illness symptoms experienced by the infants at one, three, and six months of age with positive results against cough, colds, phlegm, wheezing, fever, rash and difficulty breathing. In a double-blind, randomized placebo-controlled trial, children born to mothers who were supplemented with fish oil (2.2 g DHA and 1.1 g EPA) during pregnancy (20 weeks' gestation until delivery) displayed higher scores of eye and hand coordination at 2 1⁄2 years of age compared to children whose mothers were supplemented with olive oil.
Sperm are DHA rich particularly in the tail. The Department of Food Science and Human Nutrition at the University of Illinois recently reported from a 2011 study that DHA is necessary to construct the arch that turns a round, immature sperm cell into a pointy-headed super swimmer with an extra-long tail. “Normal sperm cells contain an arc-like structure called the acrosome that is critical in fertilization because it houses, organizes, and concentrates a variety of enzymes that sperm use to penetrate an egg," said Manabu Nakamura, an Associate Professor of Biochemical and Molecular Nutrition. Nakamura finds the role this omega 3 fatty acid plays in membrane fusion particularly exciting. Because DHA is abundant in specific tissues, including the brain and the retina as well as the testes, the scientists believe their research findings could also impact research relating to brain function and vision. "It's logical to hypothesize that DHA is involved in vesicle fusion elsewhere in the body, and because the brain contains so much of it, we wonder if deficiencies could play a role, for example, in the development of dementia. Any communication between neurons in the brain involves vesicle fusion," he noted.
