Abstract (as published in BMC Med)
A beneficial effect of a high n-3 long-chain polyunsaturated fatty acid (LCPUFA) intake has been observed in heart failure patients, who are frequently insulin resistant. We investigated the potential influence of impaired glucose metabolism on the relation between dietary intake of n-3 LCPUFAs and risk of acute myocardial infarction (AMI) in patients with coronary artery disease.
This prospective cohort study was based on the Western Norway B-Vitamin Intervention Trial and included 2,378 patients with coronary artery disease with available baseline glycosylated hemoglobin (HbA1c) and dietary data. Patients were sub-grouped as having no diabetes (HbA1c <5.7%), pre-diabetes (HbA1c ≥5.7%), or diabetes (previous diabetes, fasting baseline serum glucose ≥7.0, or non-fasting glucose ≥11.1 mmol/L). AMI risk was evaluated by Cox regression (age and sex adjusted), comparing the upper versus lower tertile of daily dietary n-3 LCPUFA intake.
The participants (80% males) had a mean age of 62 and follow-up of 4.8 years. A high n-3 LCPUFA intake was associated with reduced risk of AMI (hazard ratio 0.38, 95%CI 0.18, 0.80) in diabetes patients (median HbA1c = 7.2%), whereas no association was observed in pre-diabetes patients. In patients without diabetes a high intake tended to be associated with an increased risk (hazard ratio1.45, 95%CI 0.84, 2.53), which was significant for fatal AMI (hazard ratio 4.79, 95% CI 1.05, 21.90) and associated with lower HbA1c (mean ± standard deviation 4.55 ±0.68 versus 4.92 ±0.60, P = 0.02). No such differences in HbA1c were observed in those with pre-diabetes or diabetes.
A high intake of n-3 LCPUFAs was associated with a reduced risk of AMI, independent of HbA1c, in diabetic patients, but with an increased risk of fatal AMI and lower HbA1c among patients without impaired glucose metabolism. Further studies should investigate whether patients with diabetes may benefit from having a high intake of n-3 LCPUFAs and whether patients with normal glucose tolerance should be careful with a very high intake of these fatty acids.
The “study had limited power to detect significant effects due to the smaller sample size of the sub-groups and the low event rate primarily in the non-diabetes group” as noted by the authors. With such a low event rate of 16, the demonstration of statistical significance between tertiles cannot possibly be clinically significant.
The totality of the publicly available scientific evidence demonstrates a cardiovascular benefit of EPA and DHA in healthy populations, as well as in many populations with pre-existing cardiovascular ailments.
The list of long-chain omega-3 recommendations from professional organizations and government bodies continues to grow because the cardiovascular benefits associated with EPA and DHA are so compelling.
What Else Should You Know?
There’s no reason to believe the investigators obtained reliable information about either food and supplement intake or long-term status of long-chain omega-3 levels. That is, there are inherent limitations to the use of food frequency questionnaires to determine food and supplement intake, as well as the use of serum fatty acid levels to determine long-term long-chain omega-3 levels.
The current investigation is a prospective cohort study based on participants from the Western Norway B-Vitamin Intervention Trial, a clinical trial of 3,090 patients undergoing coronary angiography for suspected coronary artery disease who were randomized to treatment with B vitamins. Results from that study demonstrated no short- or long-term benefits on cardiovascular outcomes or all-cause mortality associated with the study treatment.
There were no differences among the three sub-groups for serum EPA and DHA. Unfortunately, within each group, the authors did not provide subject baseline characteristics among the tertiles, leaving it questionable as to whether or not there were differences.
Global Organization for EPA and DHA Omega-3s (2012). Omega-3s & Risk of Myocardial Infarction in a Diseased Population [Peer commentary on the paper “Dietary intake of n-3 long-chain polyunsaturated fatty acids and risk of myocardial infarction in coronary artery disease patients with or without diabetes mellitus: a prospective cohort study” by Strand E Pedersen ER Svingen GF Schartum-Hansen H Rebnord EW Bjørndal B Seifert R Bohov P Meyer K Hiltunen JK Nordrehaug JE Nilsen DW Berge RK and Nygård O (2013). BMC Med 11:216.].