KUOPIO, FINLAND. The three most important components of fish oil are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic acid (DPA). Extensive research has established that EPA and DHA play a vital role in the prevention of Alzheimer�s disease, atherosclerosis, heart attack, angina, stroke, congestive heart failure, depression and cancer. Clinical trials have also shown that fish oil supplementation is effective in the treatment of many disorders including high blood pressure, rheumatoid arthritis, diabetes, ulcerative colitis and Raynaud�s disease.

Now Finnish researchers report that high serum levels of EPA, DHA and DPA are associated with a significantly reduced risk of developing atrial fibrillation (AF). Their study included 2174 men enrolled in the Kuopio Ischemic Heart Disease Risk Factor Study begun in 1984-1989. The men were 42, 48, 54 or 60 years of age at the baseline examination. During 17.7 years of follow-up, 11% of the participants were found to have AF upon admission to hospital (for arrhythmia or other reasons). This corresponds to an incidence rate of 0.6% a year. NOTE: Considering that the study only included men admitted to hospital, it is clear that the population-wide incidence would be significantly higher than 0.6% a year.

At baseline, the mean percentages of EPA, DPA and DHA in serum fatty acids were 1.67%, 0.55% and 2.46% respectively. After adjustment for age and other possible confounders the researchers observed that men in the highest quartile of EPA+DPA+DHA concentration (5.3 � 15.6%) had a 35% reduced risk of developing AF when compared to men in the lowest quartile (1.7 � 3.6%). The absolute risk in the lowest quartile group was 13.4% vs 8.7% in the highest quartile group. Further analysis revealed that DHA accounted for the entire risk reduction and that EPA and DPA levels were not associated with risk of developing AF.

Considering only lone afibbers (no heart disease prior to diagnosis of AF) strengthened the association between serum fatty acid concentration of DHA and AF risk. Men in the lowest quartile had a risk of 10.9%, while those in the highest quartile had a risk of only 5.6% � a relative risk reduction of 49%.

The mean serum fatty acid concentration of alpha-linolenic acid (found in flaxseed and other vegetable oils) was 0.74% and was not related to the risk of developing AF. A hair analysis revealed no correlation between methylmercury level (methylmercury is an increasingly common contaminant of fish) and risk of AF, nor did a high methylmercury level attenuate the beneficial effects of DHA. There was also no evidence that age, hypertension, systolic blood pressure or a history of ischemic heart disease modified the association between DHA level and AF risk.

Virtanen, JK, et al. Serum long-chain n-3 polyunsaturated fatty acids and risk of hospital diagnosis of atrial fibrillation in men. Circulation, Vol. 120, December 8, 2009, pp. 2315-21

Editor�s comment: The finding that a high serum fatty acid concentration of DHA is associated with a 49% reduction in the risk of developing lone atrial fibrillation (LAF) is indeed encouraging. Unfortunately, it does not prove that a high fish intake or fish oil supplementation will reduce episode severity in patients already diagnosed with LAF. However, since LAF has a very significant genetic component fish oil supplementation could well be highly beneficial for relatives of afibbers.