Reviewed: Zare E, Alirezaei A, Bakhtiyari M, Mansouri A. Evaluating the effect of garlic extract on serum inflammatory markers of peritoneal dialysis patients: a randomized double-blind clinical trial study. BMC Nephrol. January 25, 2019;20(1):26. doi: 10.1186/s12882-019-1204-6.
Patients with end-stage renal disease who depend on maintenance dialysis are at a high risk of cardiovascular disease (CVD). In those patients, inflammation is a critical risk factor for the development of CVD. Garlic (Allium sativum, Amaryllidaceae) has been used to treat various disorders because of its many therapeutic properties, including anti-inflammatory actions. The authors conducted a parallel, randomized, double-blind, placebo-controlled clinical trial to investigate the effects of garlic on markers of inflammation and organ function in patients undergoing peritoneal dialysis.
Forty-two patients at Shafa Dialysis Center in Tehran, Iran were selected for the study. Twenty-one of those patients (aged 52.8 ± 18.2 years) were randomly assigned to a control group that received standard treatment (i.e., dialysis) and took a placebo tablet (not described) twice daily for eight weeks. The other 21 patients (aged 56.0 ± 16.0 years) also received standard treatment and took 400 mg of standardized garlic extract twice daily for eight weeks. Each garlic extract tablet contained 1 mg of alliin, a primary bioactive component of garlic. All study tablets were produced by Amin Chemical and Pharmaceutical Company in Tehran. Two patients in the garlic group transferred to other hospitals and were lost to follow-up.
The primary outcomes of this study were changes in erythrocyte sedimentation rate (ESR) and serum concentrations of the inflammatory markers interleukin 6 (IL-6) and C-reactive protein (CRP). Secondary outcomes were changes in total cholesterol and triglyceride levels, liver and renal function markers, peritoneal function tests (to measure the adequacy of peritoneal dialysis), and other biomarkers (homocysteine, sodium, potassium, phosphorus, calcium, ferritin, uric acid, and parathyroid hormone).
Fasting blood samples were collected at baseline and after eight weeks. At baseline, most of the biochemical measurements were similar between the two groups. The exceptions were lower levels of CRP (P = 0.014) and total cholesterol (P = 0.024) and higher levels of uric acid (P = 0.017) in the control group compared with the garlic group.
After eight weeks of treatment, the mean ESR was significantly lower (P = 0.027) and potassium levels were significantly higher (P = 0.039) in the garlic group compared with the placebo group. The increase in potassium levels in the garlic group is similar to findings of an earlier study that demonstrated garlic can help maintain electrolyte balance (e.g., potassium and sodium levels) and improve renal function.1
Significant reductions were seen in IL-6 (P < 0.001), CRP (P < 0.001), ESR (P = 0.021), and homocysteine levels (P < 0.001) in the garlic group compared to baseline. However, when adjusted for baseline differences, the changes in IL-6 and homocysteine over time were not significantly different between groups. Reductions from baseline in CRP (P = 0.547) and ESR (P = 0.797) in the control group were not significant. The authors concluded the standardized garlic extract taken for eight weeks significantly reduced inflammatory markers. Because increases in such markers can be life-threatening for patients on peritoneal dialysis, the authors suggest “that this safe and well-tolerated natural substance [can] be prescribed in an attempt to attenuate the inflammatory response in these patients.” In support of their findings, the authors cite a previous meta-analysis that found garlic intake reduces inflammatory markers and improves cardiovascular health by lowering pro-inflammatory cytokines.2
Because of their study’s small sample size, the authors used nonparametric tests with lower power to detect potential differences between the two groups. Trials using larger patient populations should be conducted to further explore the potential anti-inflammatory benefits of garlic in patients undergoing peritoneal dialysis.
References
- Oluwole F. Effects of garlic on some haematological and biochemical parameters. Alr J Biomed Res. April 2001;4(3):139-141. doi: 10.4314/ajbr.v4i3.53900.
- Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. J Nutr. February 2016;146(2):389S-396S. doi: 10.3945/jn.114.202192.