Effects of Omega-3 Fatty Acids on Serum Lipids, Lipoprotein (a), and Hematologic Factors in Hemodialysis Patients

Background: Lipid abnormalities, especially high serum lipoprotein (a) [Lp (a)] concentration, and anemia are two major causes of cardiovascular diseases (CVDs) in hemodialysis patients. Therefore, this study was designed to investigate the effects of marine omega-3 fatty acids on serum lipids, Lp (a), and hematologic factors in hemodialysis patients. Methods: Thirty-four hemodialysis patients were randomly assigned to either omega-3 fatty acid supplement or placebo group. Patients in the omega-3 fatty acids group received 2080 mg marine omega-3 fatty acids, daily for 10 weeks, whereas the placebo group received a corresponding placebo. At baseline and the end of week 10, 7 mL blood was collected after a 12- to 14-h fast and serum triglyceride, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), Lp (a), blood hemoglobin, hematocrit, red blood cells (RBCs), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were measured. Results: Serum triglyceride decreased significantly in the omega-3 fatty acids group at the end of week 10 compared with baseline (p < 0.05) and this reduction was significant in comparison with the placebo group (p < 0.01). No significant differences were observed between the two groups in mean changes of serum total cholesterol, LDL-C, HDL-C, Lp (a), blood hemoglobin, hematocrit, RBC, MCV, MCH, and MCHC. Conclusion: The results of our study indicate that marine omega-3 fatty acids can reduce serum triglyceride, as a risk factor for CVD, but it does not affect other serum lipids, Lp (a), and hematologic factors in hemodialysis patients.

Keywords: marine omega-3 fatty acids; hemodialysis; lipids; lipoprotein (a); hematologic factors

The most important cause of mortality in patients with chronic renal failure, including dialysis patients, is cardiovascular diseases (CVDs). The frequency of CVD in dialysis patients has been reported to be 3–45 times higher than the general populations and approximately 50% of deaths in these patients are related to CVD.[[1]] In hemodialysis patients, one of the major risk factors for CVD is lipid abnormalities including low serum high-density lipoprotein cholesterol (HDL-C), high serum triglyceride, very low-density lipoprotein cholesterol (VLDL-C), intermediate-density lipoprotein cholesterol, and particularly lipoprotein (a) [Lp (a)].[[3]] Serum Lp (a) concentration higher than 30 mg/dL, a prevalent lipid abnormality in hemodialysis patients, is an important risk factor for CVD.[[4], [7]] On the other hand, anemia is one of the most common complications in hemodialysis patients which not only lowers their quality of life, but also potentially causes CVDs such as congestive heart failure.[[12]]

At the present time, blood lipid-normalizing drugs such as statins, nicotinic acid, fibric acid derivatives, and so on are used to treat lipid abnormalities and prevent CVD in hemodialysis patients; however, no effective treatment to reduce Lp (a) concentration in these patients has been known so far.[4] Few studies have been done about the effect of omega-3 fatty acids supplement on serum Lp (a) concentration, and the findings of these studies have been contradictory. Some of these studies in nonuremic patients have shown that omega-3 fatty acids supplement could reduce serum Lp (a) concentration,[14] whereas other researches did not indicate these effects in hemodialysis patients.[[15]] In addition, limited studies on the effect of omega-3 fatty acids supplement on hematologic factors are available, and their results are controversial. Some studies showed that omega-3 fatty acids supplement increased blood hemoglobin[18] and reduced erythropoietin requirements,[19] whereas other studies did not indicate these effects in hemodialysis patients.[[20]]

Considering the scarcity of studies on the effects of omega-3 fatty acids supplement on serum Lp (a) and blood hematologic factors in hemodialysis patients, this study was designed to investigate whether the use of marine omega-3 fatty acids supplement can correct lipid abnormalities, particularly high serum Lp (a) concentration, and improve blood hematologic factors in hemodialysis patients.

This study was a randomized, double-blind, placebo-controlled trial. Thirty-four adult hemodialysis patients (21 men and 13 women) in the age range of 19–76 years were recruited from hemodialysis unit of Vaseii Hospital in Sabzevar, Iran. Patients enrolled in this study did not have inflammatory diseases or infectious diseases including hepatitis, and none of them received omega-3 fatty acids supplement, l-carnitine supplement, and steroidal and/or nonsteroidal anti-inflammatory drugs. All participating patients were dialyzed with polysulfone capillary dialyzers three times a week for 4 h per session except two patients with two times per week. During this study, the hemodialysis procedure and type of dialyzer were not altered for any of the patients.

The study protocol was approved by the Ethics Committee of the National Nutrition and Food Technology Research Institute of Iran. This study was in adherence with the Declaration of Helsinki. Written informed consent was obtained from all patients.

Patients were randomly allocated to either omega-3 fatty acids or placebo group. Subjects in the omega-3 fatty acids group received 2080 mg marine omega-3 fatty acids as four capsules (MaxEPA®, Seven Seas Health Care Ltd., Hull, UK), each containing 310 mg eicosapentaenoic acid and 210 mg docosahexaenoic acid, daily for 10 weeks, whereas the placebo group received four corresponding placebo capsules containing medium chain triglycerides oil. Subjects were advised not to change their dietary habits, physical activities, and drug regimens. At baseline and the end of week 10, 7 mL blood was collected from each patient after a 12- to 14-h fast before hemodialysis.

Blood samples were divided into two test tubes in equal volumes. The first tube, containing 3% ethylenediaminetetraacetate as an anticoagulant, was used to measure hematologic factors. The second tube, without any anticoagulant, was centrifuged at 1000 × g for 15 min to separate sera.

Serum concentrations of triglycerides, total cholesterol, and HDL-C were measured enzymatically using commercial kits (Pars Azemoon Co., Tehran, Iran), with the aid of a Hitachi 717 auto-analyzer (Boehringer Mannheim Diagnostics, Mannheim, Germany). The coefficient of variation (CV) for serum lipids was less than 5%. As serum triglyceride concentration in all participating patients was less than 400 mg/dL, serum low-density lipoprotein cholesterol (LDL-C) was estimated using the Friedewald equation.[22] Serum Lp (a) concentration was determined with the use of enzyme-linked immunosorbent assay kits (Mercodia AB, Uppsala, Sweden). The CV for serum Lp (a) was 2.3%. Blood hemoglobin, hematocrit, red blood cells (RBCs), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC) were measured with the aid of a Cobas Micros Cell Counter (Roche Diagnostic Systems, Montpellier, France). The CV for hematologic factors was less than 1.7%.

Patients were weighed after hemodialysis to determine dry body weight at baseline and the end of weeks 5 and 10. In addition, the dietary intakes of subjects were assessed using a 2-day dietary recall (one dialysis day and one non-dialysis day) at baseline and the end of weeks 5 and 10. Patients' diets were analyzed by Nutritionist-IV software (N-Squared Computing, San Bruno, CA, USA).

Dialysis adequacy based on Kt/V index was determined for each patient at baseline by a Kt/V calculator software using information recorded in patient files, including predialysis blood urea nitrogen (BUN) concentration, postdialysis BUN, the dialysis session length, postdialysis weight, and ultrafiltration volume.[23]

To ascertain patients' compliance, we provided each patient with a fixed number of capsules and instructions to return the unconsumed capsules at the end of this study. According to the number of returned capsules, the degree of compliance for each patient was determined. In this study, the compliance of all patients was more than 90%.

Statistical analysis of the data was performed using Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL, USA) for Windows version 15.0. The χ2 test was used to compare qualitative variables between the two groups. Because all quantitative parameters according to the Kolmogorov–Smirnov test had normal distributions, we used t-test and paired t-test to compare parameters between and within groups, respectively. In addition, because dietary and anthropometric parameters were measured three times during the study, analysis of variance for repeated measurements was used to compare data between various times. The results are expressed as mean ± SD, and differences were considered significant at p ≤ 0.05.

Table 1. Baseline characteristics of hemodialysis patients in the omega-3 fatty acids and placebo groups.

6 Note: Age, duration of dialysis, and dialysis adequacy are presented as mean ± SD.

Table 2. Anthropometric and dietary factors in the omega-3 fatty acids and the placebo groups.

7 Notes: All values are presented as mean ± SD. n = 17 for all values. BMI, body mass index; MUFA, monounsaturated fatty acids; SAFA, saturated fatty acids; PUFA: polyunsaturated fatty acids.

The baseline characteristics of patients did not differ significantly between the two groups (Table 1).

Anthropometric and dietary factors were not significantly different between the two groups at baseline and the end of weeks 5 and 10. In addition, these factors did not significantly change within each group during the study (Table 2).

Serum triglyceride concentration decreased significantly in the omega-3 fatty acids group at the end of week 10 compared with baseline (p < 0.05), whereas no significant change was observed in the placebo group. The reduction of serum triglyceride concentration in the omega-3 fatty acids group was statistically significant in comparison with the placebo group (p < 0.01; Table 3).

Table 3. Serum concentrations of lipids, Lp (a), and blood hematologic parameters in the omega-3 fatty acids and the placebo groups.

• 8 Notes: All values are presented as mean ± SD. n = 17 for all values. LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; MCV, mean corpuscular volume; MCH, mean corpuscular hemoglobin; MCHC, mean corpuscular hemoglobin concentration.
• 3001 aChanges reflect week 10—baseline values.
• 9 *, **, and *** Denote p < 0.01 versus baseline, p < 0.05 versus baseline, and p < 0.01 versus the placebo group, respectively.

Serum concentrations of Lp (a) and total cholesterol did not significantly change in the omega-3 fatty acids group during the study, whereas significant increases were observed in serum concentrations of Lp (a) (p < 0.01) and total cholesterol (p < 0.05) in the placebo group (Table 3). Nonetheless, the increases of serum Lp (a) and total cholesterol in the placebo group were not statistically significant in comparison with the omega-3 fatty acids group (Table 3).

Serum concentrations of HDL-C and LDL-C did not significantly change within each group during the study (Table 3).

There were no significant differences between the two groups with regard to mean dose of intravenous erythropoietin and mean intake of oral iron and folic acid supplements during the study period (Table 4).

Table 4. Mean dose of intravenous erythropoietin and the intake of oral iron and folic acid supplements during the study period in both groups.

10 Notes: All values are presented as mean ± SD. n = 17 for all values.

The number of RBCs increased in both groups at the end of week 10 compared with baseline (p < 0.05). However, these increases were not significantly different between the two groups (Table 3). Blood hemoglobin did not significantly change within each group during the study (Table 3).

Blood hematocrit reduced significantly in the omega-3 fatty acids group at the end of week 10 compared with baseline (p < 0.05), whereas the reduction of blood hematocrit in the placebo group was marginally significant (p = 0.06; Table 3). No significant difference was observed between the two groups in mean changes of blood hematocrit.

MCV and MCH decreased in both groups at the end of week 10 compared with baseline (p < 0.01). However, these reductions were not significantly different between the two groups (Table 3).

MCHC increased in both groups at the end of week 10 compared with baseline (p < 0.01). However, the increases were not significantly different between the two groups (Table 3).

High serum Lp (a) concentration is a common lipid disorder in dialysis patients,[[4], [11]] and Lp (a) hyperlipoproteinemia constitutes a major risk factor for CVD.[[7]] However, no effective treatment to reduce Lp (a) in these patients has been known so far.[4] Few studies on the effect of omega-3 fatty acids on serum Lp (a) are available. In this study, serum Lp (a) concentration did not significantly change in omega-3 fatty acids group. This finding was in agreement with those of some previous studies in hemodialysis patients.[[15]] In contrast to our study, Herrmann et al.[14] showed that omega-3 fatty acids supplement significantly reduced serum Lp (a) concentration in nonrenal failure patients. This disparity may be because of the fact that Herrmann et al.'s[14] research was conducted in nonrenal failure subjects and dosage of omega-3 fatty acids supplement was 8.5 g/d. It should be noted that according to the Food and Drug Administration, the daily intake of more than 3 g of omega-3 fatty acids is not safe.[19]

In this study, omega-3 fatty acids supplement decreased serum triglyceride concentration during 10 weeks and this reduction was significant as compared with the placebo group. This finding was in agreement with those of the majority of previous studies.[[15], [24]]

Omega-3 fatty acids inhibit hepatic synthesis of fatty acids and consequently triglycerides by suppressing gene expression of sterol regulatory element-binding proteins and enhancement of their proteasome degradation, which result in reduced gene expression of enzymes involved in fatty acids synthesis, that is, acetyl-coenzyme A carboxylase and fatty acid synthetase complex.[[34]] Reduced synthesis of fatty acids and triglyceride in liver causes a decrease in VLDL formation and consequently reduces serum triglyceride concentration.

In our study, the administration of marine omega-3 fatty acids supplement for 10 weeks had no significant effect on serum total cholesterol and LDL-C. In agreement with these findings, the majority of previous studies have shown that omega-3 fatty acids caused no changes in serum total cholesterol[[15], [21], [27], [30], [33]] and LDL-C.[[15], [27], [33]] In contrast, some studies have indicated that omega-3 fatty acids reduce serum concentrations of total cholesterol[[26], [29]] and LDL-C.[[25], [32]] These contradictory findings may be because of the duration and dosage of omega-3 fatty acids supplementation, as well as differences in baseline serum levels of total cholesterol and LDL-C. As is usual in hemodialysis patients, serum total cholesterol and LDL-C were normal in our study participants; therefore, omega-3 fatty acids supplement was not expected to have any effect on serum total cholesterol and LDL-C.

In our study, marine omega-3 fatty acids supplement had no effect on serum HDL-C, a finding that is in agreement with those of some previous studies.[[15], [21], [24]] In contrast, some researchers have indicated omega-3 fatty acids supplement increased serum HDL-C.[[18], [26], [32]] These controversial findings may be due to baseline serum concentrations of HDL-C and triglyceride. It has been shown that the reduction of serum triglyceride concentration causes an increase in serum HDL-C.[37] In our study participants, serum triglyceride concentration was in normal range; therefore, the reduction of serum triglyceride by omega-3 fatty acids supplement was slight and could not increase serum HDL-C.

During the study period, there were no significant differences between the two groups with regard to mean dose of intravenous erythropoietin and mean intake of oral iron and folic acid supplements. The number of RBCs increased significantly in both groups during the study period. This is due to the administration of intravenous erythropoietin. However, the increases of RBCs were not significantly different between the two groups. The fact indicates that omega-3 fatty acids supplement has no effect on RBC production. This finding was in accordance with that of Vernaglione et al.,[20] who observed daily administration of 2 g omega-3 fatty acids supplement to hemodialysis patients, for 4 months, had no effect on the number of RBCs.

In this study, marine omega-3 fatty acids supplement caused no change in blood hemoglobin. This result is in agreement with that of Vernaglione et al.'s[20] study. In addition, Donnelly et al.[21] showed that daily administration of 3.6 g omega-3 fatty acids supplement to hemodialysis patients, for 4 weeks, had no effect on blood hemoglobin. In contrast, Perunicic-Pekovic et al.[18] indicated, in a quasi-experimental study, that the daily administration of 2.4 g omega-3 fatty acids supplement, for 4 months, increased significantly blood hemoglobin in hemodialysis patients. This disparity may be due to the fact that Perunicic-Pekovic et al.'s[18] study had no control group.

During the study period, blood hematocrit reduced in both groups. The fact shows that marine omega-3 fatty acids supplement has no effect on blood hematocrit. The reduction of blood hematocrit in both groups may be due to a decrease in RBC volume (or MCV). In our study, MCV reduced significantly in the two groups. With respect to the lack of significant difference between the two groups in mean daily folic acid intake, the reduction of MCV in the two groups at the end of week 10 compared with baseline may be because of the fact that the patients, at the beginning of the study, were advised to use their folic acid supplements regularly. It should be noted that folic acid deficiency can cause an increase in RBC volume.[38] In agreement with our study, Donnelly et al.[21] showed that omega-3 fatty acids supplement had no effect on blood hematocrit in hemodialysis patients. We found no research in available literature about the effect of omega-3 fatty acids supplement on MCV to be compared with our results.

During the study period, MCH decreased in both groups. The fact showed that marine omega-3 fatty acids supplement had no effect on blood MCH. MCH is calculated by dividing blood hemoglobin concentration by the RBC count.[38] In our study, blood hemoglobin did not change in both groups; therefore, the reduction of MCH in the two groups was due to an increase in the number of RBCs. During the study period, MCHC increased in both groups; however, the increases were not significantly different between the two groups. MCHC is calculated by dividing blood hemoglobin by hematocrit value.[38] In this study, marine omega-3 fatty acids supplement had no effect on blood hemoglobin in both groups; therefore, the increase of MCHC in the two groups was due to a reduction in hematocrit value. We found no research in available literature about the effect of omega-3 fatty acids supplement on MCH and MCHC to be compared with our results.

We did not determine the fatty acid composition of erythrocyte membrane phospholipids, and this was a limitation of our study.

In conclusion, marine omega-3 fatty acids supplement can reduce serum triglyceride concentration, as a risk factor for CVD, but it does not affect other serum lipids, Lp (a), and hematologic factors in hemodialysis patients.

The authors thank the staff of Hemodialysis Unit of Vaseii Hospital in Sabzevar for their invaluable assistance and the staff of the research laboratory of Research Institute for Endocrine Sciences for their technical assistance. The authors also gratefully acknowledge the cooperation of the participating patients, without whom this investigation would not have been possible.

Funding. This study was supported by National Nutrition and Food Technology Research Institute of Iran.

Declaration of interest : The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.