Docosahexaenoic Acid (DHA) (Fish Oil) (See also EPA)

James Meschino DC, MS, ROHP
General Features
DHA is an omega-3 fatty acid that is found in fish oil along with EPA (Eicosapentaenoic Acid).  Unlike EPA, DHA does not directly participate in the formation of prostaglandins or eicosanoids (hormone-like substances produced by local tissue).  However, DHA can be converted to EPA, which is the immediate precursor of prostaglandin series-3.  It also appears that unlike EPA, DHA may not reduce platelet clotting behaviour.^1,2,3

DHA is one of the most abundant fatty acids in the brain, where it is required for normal growth and development of the brain, nervous system and retina.  DHA is essential for normal visual and neurological development in infants.^4,5  Double-blind evidence links DHA supplementation in premature infants to better brain functioning.⁶

DHA has been shown to reduce levels of blood triglycerides.¹

Supplementation Studies and Clinical Applications

1. Eczema

Supplementation with various essential fatty acids has been shown to be beneficial in the treatment of eczema.  Although good results have been reported with gamma-linolenic acid, flaxseed oil or fish oil supplementation, studies seem to show that the degree of improvement correlates with the increased concentration of DHA in serum phospholipids.  Thus fish oil supplementation may be the preferred essential oil supplement for these patients.⁷

2. Asthma

Increasing DHA and EPA intake (through supplementation) can improve asthma in children by reducing the concentrations of arachidonic acid.  Arachidonic acid is the precursor of inflammatory 4-series leukotrienes.  The ingestion of fish oil supplements shifts leukotrienes synthesis from series 4 to series 5, which are less inflammatory, helping to relieve asthma symptoms and improving respiratory function.^8,9,10

3. Attention Deficit Hyperactivity Disorder (ADHD)

Some evidence suggests that children with ADHD may have significantly lower proportions of plasma Docosahexaenoic Acid, which may reflect an impairment in the ability to convert EPA into DHA, or enhance metabolism of EPA and DHA.

Burgess et al, are conducting a large intervention trial with ADHD children to see if essential fatty acid supplementation yields an improvement over placebo.¹¹

4. Nerve Conduction

Individuals with a genetic disorder known as Zellweger Syndrome are known to have low levels of DHA.  DHA supplementation in these individuals has demonstrated improvement in nerve myelination and nerve impulse conduction, helping to improve muscle and vision function.¹⁵

Dosage Ranges
Therapeutic use of DHA is usually in the range of 1-3 gms of DHA from fish oil, most commonly 250 – 1,000 mg per day.¹⁶

Adverse Side Effects and Toxicity
See EPA (Eicosapentaenoic Acid)

Contraindications and Drug-Nutrient Interactions
Fish oil supplementation may increase blood cholesterol and at high doses may increase insulin resistance in diabetics, who should not exceed 2.5 gm of fish oil per day (taken as a supplement).  Unlike EPA, DHA does not potentiate the effects of anti-coagulant drugs and therefore, is not contraindicated with their use.

There are no well-known drug-nutrient interactions for DHA.^12,13,14

References

1. Davidson MH, Maki KC, Kalkowski J, Schaefer EJ, Torri SA, Drennan KB. Effects of docosahexaenoic acid on serum lipoproteins in patients with combined hyperlipidemia: A randomized, double-blind, placeb-controlled trial.  J Am coll Nutr 1997:16,3:236-43.
2. Conquer JA, Holub BJ. Supplementation with an algae source of DHA increases (n-3) fatty acid status and alters selected risk factors for heart disease in vegetarian subjects.  J Nutr 1996;126:3032-9.
3. Nelson GJ, et al. The effect of dietary DHA on platelet function, platelet fatty acid composition, and blood coagulation in humans.  Lipids 1997;32:1129-36.
4. Gibson RA, Neumann MA, Makrides M. Effect of dietary DHA on brain composition and neural function in term infants.  Lipids 1996;31(Suppl):1775S-81S.
5. Makrides M, Neumann MA, Gibson RA. Is dietary DHA essential for term infants?  Lipids 1996;31:115-9.
6. Werkman SH, Carlson SE. A randomized trial of visual attention of preterm infants fed DHA until nine months.  Lipids 1996:31:91-7.
7. Soyland E, et al. Dietary supplementation with very long-chain n-3 fatty acids in patients with atopic dermatitis: a double-blind, multi-centre study.  Br J Dermatol 1994;130:757-64.
8. Arm JP, et al. The effects of dietary supplementation with fish oil lipids on the airway response to inhaled allergen in bronchial asthma.  Am Rev Respiratory Dis 1989;139:1395-400.
9. Dry J, et al. Effect of a fish oil diet on asthma: Results of a 1-year double-blind study.  Int Arch Allergy Apply Immunol 1991;95:156-7.
10. Broughton KS, Johnson CS, Pace BK, Liebman M, Kleppinger KM. Reduced asthma symptoms with n-3 fatty acid ingestion are related to 5-series leukotriene production.  Am J Clin Nutr 1997;65:1011–7.
11. Burgess JR, Stevens L, Zhang W, Peck L. Long-chain polyunsaturated fatty acids in children with attention-deficit hyperactivity disorder.  Am J Clin Nutr 2000;71,7(Suppl):327S-30S.
12. Schectman G, Kaul S, Kassebah AH. Effect of fish oil concentrate on lipoprotein composition in NIDDM.  Diabetes 1988;37:1567-73.
13. Axelrod L. Effects of a small quantity of omega-3 fatty acids on cardiovascular risk factor in non-insulin dependent diabetics(NIDD).  Diabetes Care 1994;17:37-45.
14. Healthnotes Healthnotes Inc 2000:DHA.
15. Martinez M. Resortin the DHA levels in the brains of Zellweger patients.  J Mol Neurosci 2001;85(6):966-74.
16. Dietary Supplementation Information Bureau. content.intramedicine.com:DHA.