Dialysis Patients May Benefit from Omega-3 Fatty Acids
Fish are a good source of omega-3 fatty acids.
In the general population, high consumption or supplementation with omega-3 fatty acids is associated with decreased serum triglycerides, serum low density lipoproteins, BP, and pulse pressure, all risk factors for cardiovascular disease (CVD) (Clin Exp Hypertens. 2010;32:137-144).
CVD is the number one cause of death in CKD patients (Am J Kidney Dis. 1998;32:S1-S162) and many of the same risk factors exist in CKD patients that are in the general population, such as hypertriglyceridemia.
However, it cannot be assumed that omega-3 fatty acids will have an effect in the CKD population similar to that observed in the general population. Some cardiovascular risk factors such as elevated BMI are reversed in CKD patients, especially in the later stages (Nephrol Dial Transplant. 2009;2421-2428).
Recent studies suggest that statins, the traditional medications for reducing cardiovascular event risk, have minimal effect in CKD or end-stage renal disease (ESRD) patients (Curr Opin Nephrol Hypertens. 2006;15:566-570). Therefore, omega-3 fatty acids as a lower cost therapy for CVD may be of some value.
Importance of Omega-3's
Omega-3 fatty acids may have a positive impact on BP, low-density lipoproteins, and inflammation. There are two types of essential fatty acids: omega-3 and omega-6. Both of these fatty acids have 18 carbons and are metabolized to arachidonic and eicosapentaenoic acids.
These fatty acids are the precursors for anti-inflammatory compounds such as lipooxin, protectins, and nitrolipids (Lipids Health Dis. 2008;7:37). Additionally, the fatty acids are linked to lipoprotein (a) levels. Lipoprotein (a) or Lp(a), is a risk factor for heart disease. It is thought that by increasing the body pool of omega-3 fatty acids and lowering omega-6 fatty acids, Lp(a) concentrations and inflammatory processes may be lowered and subsequently CVD risk would be decreased.
Clinical trial evidence
Several trials have used omega-3 supplements as a treatment to test this hypothesis. One randomized, double-blind intervention trial investigated whether omega-3 fatty acids, used as a secondary prevention treatment, would reduce the incidence of cardiovascular events and death (Clin J Am Soc Nephrol 2006;1:780-786). The study population included 206 patients randomized to either two capsules containing a total of 1.7 g of omega-3 fatty acid or identical placebo capsules for 24 months.
The primary outcome of this study was a composite of acute myocardial infarction (MI), angina pectoris requiring coronary investigation or intervention, stroke, transient ischemic attack, peripheral vascular disease requiring surgical intervention, or death. The researchers found no significant difference between groups in the composite outcome, but the omega-3 fatty acid group had significantly fewer MIs than the placebo arm (4 vs. 13). The two groups had similar rates of significant adverse events.
In a secondary analysis by the same group, significant differences were observed in lipid concentrations (Nephrol Dial Transplant. 2008;23:2918-2924). In this analysis, after three months of supplementation, 103 members of the treatment group had a significant decrease in serum triglycerides while no change was observed in total cholesterol, high- and low-density cholesterol or Lp(a) or apoprotein B.
In another randomized, double-blind study (J Ren Nutr. 2009;19:443-449), 33 ESRD patients took either over-the-counter fish oil supplements containing eicosapentaenoic acid (0.96 g/day) and docosahexaenoic acid (0.6 g/day) or corn oil (controls) for six months. The two groups had similar baseline characteristics. At six months, investigators observed no significant difference between the treatment and control groups in Lp(a) level, the primary outcome. The results of this study may be due to a lack of power in the sample or the lower dose of omega-3 fatty acids used for treatment.
Benefits for dialysis patients
The available studies do not provide enough evidence to recommend omega-3 supplements for all patients on dialysis. These data do hint that omega-3 fatty acid supplements lower serum lipid concentrations and may be effective in reducing the incidence of MIs.
However, additional well controlled and well-powered studies will need to be conducted to determine which patients are most likely to benefit from omega-3 fatty acids and the optimal dose. Although there were no reports of adverse effects in the aforementioned studies, fishy odors and burping have been observed in other studies looking at high-dose omega-3 supplements.
Food sources rich in omega-3 fatty acids include flaxseeds, walnuts, chinook salmon, sardines, cooked soybeans, baked or broiled halibut, steamed or broiled shrimp, raw tofu, baked or broiled snapper, and baked or broiled scallops.
Interestingly, the omega-3 fatty acids in fish are thought to be absorbed better than the fatty acids from flaxseed oil because the omega 3 in fatty fish are transported via triglycerides and have more efficient absorption through the gut wall. Increased intake of foods rich in omega-3 fatty acids or a daily supplement is an inexpensive method to potentially reduce serum triglyceride levels and may decrease patients risk for cardiovascular events such as MIs.
Dr. Steiber is Coordinator of the Dietetic Internship/Master's Degree Program at Case Western Reserve University in Cleveland.