Asystematic review of data on the risks and benefits of omega-3 fatty acids showed no clear benefit for mortality, cardiovascular disease, stroke, or cancer.
In a metaanalysis that included 48 randomized, controlled trials and 41 cohort studies, Lee Hooper, Ph.D., of the University of East Anglia, Norwich, England, and colleagues determined that the lack of effect was even more pronounced when studies with a high risk of bias were excluded (BMJ March 24, 2006;doi:10.1136/bmj.38755.366331.2F).
This result contradicts previous reviews of omega-3 trials that did show a beneficial effect on mortality, perhaps in part because the metaanalysis by Hooper et al includes the recently published results of a large trial. These results differed from the findings of the other large studies on this topic.
Altogether, the metaanalysis included nearly 37,000 participants in randomized, controlled trials as well as more than 560,000 participants in cohort trials. Some of the trials examined consumption of oily fish, while others studied subjects who took supplements.
In an editorial, Eric Brunner, Ph.D., of the Royal Free and University College London Medical School, emphasized that despite the results of this metaanalysis, there still remains good evidence that omega-3 fatty acids are beneficial for health. Extreme nutritional deficiency of these fats results in neuropathy, for example (BMJ March 24, 2006;doi:10.1136/bmj.38798.680185.47).
Furthermore, adequate intake of omega-3 fats is particularly important for women of childbearing age, since an estimated 25 g of maternal docosahexaenoic acid is needed during pregnancy and lactation to support the development of the child's brain.
But Dr. Brunner pointed to a paradox. Although nutrition experts advise increasing consumption of oily fish containing omega-3 fatty acids, industrial fishing has depleted the world's fish stocks by about 90% since 1950, and therefore the world probably doesn't have a sustainable supply of these fats.