BOSTON, MASSACHUSETTS. Experimental studies suggest that long-chain omega-3 (n-3) polyunsaturated fatty acids (n-3 PUFA) may help prevent the development of atrial fibrillation (AF). However, most studies involving humans have used food frequency questionnaires to estimate the intake of the three main n-3 PUFAs � eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). EPA, DPA and DHA are the main components of fish oil extracted from the tissue of oily fish such as herring, salmon and tuna.

A group of researchers from Harvard Medical School, Harvard School of Public Health, University of Western Australia, University of Washington, University of New Mexico, Fred Hutchinson Cancer Research Center, and Brigham and Women�s Hospital now reports the results of a major study (funded by the National Heart, Lung, and Blood Institute in the US) aimed at determining the association between actual circulating blood levels (measured in the phospholipid fraction) of n-3 PUFAs and the development of AF in an older population.

The study included 1330 men and 1996 women who were free of AF and heart failure at enrolment in 1992 to 1993. During 31,169 person-years of follow-up, 789 participants were diagnosed with AF. After extensive adjustment for likely confounders (demographic, cardiovascular, and lifestyle risk factors), the researchers conclude that having an average n-3 PUFA level (measured as percentage of total phospholipid fatty acids in blood plasma) of 6.3% is associated with a 29% reduced risk of developing AF when compared to a total n-3 PUFA level of 2.9%. This corresponds to a risk decrease of 9% for each 1% increase in n-3 PUFA level.

An analysis of the effect of the individual components of n-3 PUFA (EPA, DPA and DHA) showed that only the association with DHA was statistically significant with a corrected risk reduction of 23% at an average phospholipid level of 4.4% as compared to a level of 2.0%, corresponding to an approximate 10% reduction in risk for each 1% increase in DHA level. The researchers point out that DHA is present in significantly higher (3- to 9-fold higher) levels in heart tissue (myocardial membranes) than are EPA and DPA. DHA has, in separate studies, been found to augment vagal activity, lower heart rate and blood pressure, and to favorably modulate myocytes ion channels.

The researchers conclude that higher circulation levels of n-3 PUFAs and, in particular, DHA are associated with a reduced risk of developing AF in older adults and recommend further studies to determine whether an increased dietary intake of n-3 PUFAs (fish oils) would be effective in the primary prevention of AF.
Wu, JHY, et al. Association of plasma phospholipid long-chain omega-3 fatty acids with incident atrial fibrillation in older adults. Circulation, Vol. 125, March 6, 2012, pp. 1084-93

Editor�s comment: In considering the conclusions reached in the above study, it should be kept in mind that they are not necessarily applicable to the prevention of lone AF in younger, healthy people. Not only were the participants in the above study older (average age of 74 years at baseline) but almost half had hypertension, 20% had coronary heart disease, and 15% had diabetes. Furthermore, endurance athletes and other highly physically active people are likely to develop the vagal form of AF, for which fish oil supplementation may not be beneficial.