NEW YORK (Reuters Health) Mar 23 - British researchers who conducted a meta-analysis of trials found no strong evidence that consuming omega 3 fatty acids for at last 6 months has a clear effect on mortality, cardiovascular events, or cancer.

UK guidelines encourage consumption of more oily fish, especially after myocardial infarction, Dr. Lee Hooper and associates note in their report, published in BMJ Online First on March 23.

To see if such recommendations are justified, Dr. Lee, from the University of East Anglia in Norwich, and colleagues reviewed 48 randomized control trials (RCTs) that included nearly 37,000 participants, and 41 prospective cohort studies that included more than 570,000 subjects.

When including all RCTs, the relative risk (RR) of death was 0.87 among subjects assigned to omega 3; however, the authors note that the evidence was "weak" and that "inconsistency was moderate." When they evaluated the 25 RCTs rated as having a low risk of bias, the RR was 0.98. Results were similar for long chain versus short chain omega 3, and for dietary advice versus supplements.

In the cohort studies, omega 3 seemed to protect against death (RR 0.65), but the authors note that adjustment for confounders may not have been adequate.

The 18 RCTs that examined cardiovascular events yielded an RR of 0.95 with wide confidence intervals and high inconsistency.

Ten RCTs and seven cohort studies that evaluated cancer incidence showed no protective effect (RR 1.07 and 1.02, respectively).

Dr. Hooper's team advises that the general public should still be encouraged to eat more oily fish after MI, "but evidence should be reviewed regularly." They add, "It is probably not appropriate to recommend a high intake of omega 3 fats for people who have angina but have not had a myocardial infarction."

In a related editorial, Dr. Eric Brunner, from Royal Free and University College London Medical School, points out the added complication that the supply of oily fish is dwindling due to overfishing. Therefore, "we probably do not have a sustainable supply of long chain omega fats."