DOCOSAHEXAENOIC ACID (DHA) AND DIETARY RECOMMENDATIONS

Introduction :

Docosahexaenoic acid (DHA) is an omega -3 long chain polyunsaturated fatty acid (LC-PUFA). It is derived from alpha linolenic acid (ALA) which is an essential fatty acid and is not synthesized in the body. DHA has important roles in the visual and neurological functions. DHA is concentrated in the membrane lipids of gray matter and in the visual elements of the retina.

The supply of long-chain n-3 fatty acid DHA in the overall population, as well as in children and adolescents, is often inadequate. In the eating habits prevalent in western industrial countries, food tends to be rich in n-6 fatty acids such as linoleic acid (LA) and arachidonic acid (AA), and low in long-chain n-3 fatty acids such as Eicosapentaenoic acid (EPA) and DHA. (1) DHA is predominant in fish (salmon, mackerel or herring) and seafood and consumption of these foods in Indian children is virtually lacking. Although fish oils are rich sources of DHA, most commercially available fish oils contain higher amount of EPA than DHA. Most DHA found in extracted fish oil preparation is derived from microalgae consumed by the fish. Pure DHA from fish oil is not readily available in the commercial market due to difficulties in extraction and purification processes. Currently, the best commercial source of DHA is derived from microalgae by fermentation which is the vegetarian source of DHA. (2) This vegetarian source of commercial microalgae DHA may have to be supplemented in children to achieve adequate DHA content.

Dietary recommendations for DHA :

According to the state of knowledge today, a minimum amount of the n-3 fatty acids EPA and DHA, i.e., 0.1 to 0.2 g/d, is needed in order to maintain essential body functions; in contrast, intake amounts of 0.3 to 0.4 g per day are regarded as nutritionally desirable (1). To guarantee adequate neuronal development in the fetus or infant, requirements for maternal diet during pregnancy and breast-feeding rise by 0.15 up to 0.35 g n-3 fatty acids per day (1) Recommendations for fish or DHA+EPA intakes for healthy adults have been developed by government health agencies worldwide (1). The recommendations range from 200 to 670 mg/day (3). Recent draft regulations from the European Food Safety Authority (EFSA) recommend an intake of 250 mg/day of DHA plus EPA for adults and an additional 100 mg/day of DHA for a pregnant woman (3). For infants and children, EFSA recommends 20–50 mg/day of DHA in the 0–6 months period and 100 mg/day in the 6–24 months period. Dietary intakes for children 2–18 years of age should be consistent with intakes for the adult population ( 250 mg of DHA plus EPA per day) (4).

Both omega 6 and omega 3 essential fatty acids compete for the same enzymes and have different biological roles, the balance between the n-6 and the n-3 fatty acids in the diet is of considerable importance. According to the recommendations of nutrition societies from Germany, Austria and Switzerland, children, teenagers and adults should, while reducing their fat consumption to 30% and taking a n-6 to n-3 ratio of 5:1 into account, derive roughly 0.5% of their total energy in the form of n-3 fatty acids (1)

Recently, the Technical Committee on Dietary Lipids of the International Life Sciences Institute of North America sponsored a workshop to consider whether the evidence related to coronary heart disease, cancer, and cognitive decline had progressed sufficiently to justify reconsideration of a daily recommended intake for DHA and EPA (1). The workshop concluded that the data for coronary heart disease prevention support a DRI for DHA+EPA between 250 and 500 mg/day. The Scientific Advisory Committee on Nutrition from the United Kingdom (2) encourages consumption of at least 2 (140 g) servings of fish per week with at least one of these servings from fatty fish. The recommendation to eat more fatty types of sea fish (one to two times a week) is, however, in conflict with the reluctance of many children to eat fish at all. DHA content in various fish is depicted in Table 1.

Table 1: DHA content in various fish (100g, raw) (6)

Supplementation of DHA :

With respect to DHA, a supplement (or fortified food) would be advised for vegans, individuals who are allergic or cannot eat fish, who do not like fish, or who elect to not include it in their diet. In addition, some individuals cannot meet the levels of EPA and DHA recommended by diet. (7)

Conclusion :

Numerous recommendations for long-chain omega-3 fatty acid intakes have been made globally by many federal agencies, professional groups, and scientists. The majority of recommendations have been issued on the basis of amount of EPA+DHA together, without specific guidance for each fatty acid. There is often a difference between the desired recommended intake and actual intake, as the content of n-3 fatty acids in the prevailing modern diet is extremely low.

References :

1.	Schuchardt JP, Huss M, Stauss-Grabo M, Hahn A. Significance of long-chain polyunsaturated fatty acids (PUFAs) for the development and behaviour of children. Eur J Pediatr. 2010;169:149-64.
2.	http://www.martek.com/About/Martek-Products.aspx. Accessed October 23, 2009.
3.	Harris WS, Mozaffarian D, Lefevre M et al., Towards establishing dietary reference intakes for eicosapentaenoic and docosapentaenoic acids, J. Nutr. 2009; 139: 804S-819S.
4.	European Food Safety Authority, Draft scientific opinion of the Panel of Dietetic Products, Nutrition and Allergies on a request from the European Commission related to dietary reference values for fats, EFSA J. 1-97, in press.
5.	Scientific Advisory Committee on Nutrition, The Nutritional Wellbeing of the British Population, The Stationary Office, Norwich, UK, 2008.
6.	Agricultural Research Service, USDA National Nutrient Database for Standard Reference, Nutrient Data Laboratory.
7.	Kris-Etherton PM, Grieger JA, Etherton TD. Dietary reference intakes for DHA and EPA. Prostaglandins Leukot Essent Fatty Acids. 2009; 81: 99-104.