Reviewed: Yu S, Yue SW, Liu Z, Zhang T, Xiang N, Fu H. Yerba mate (Ilex paraguariensis) improves microcirculation of volunteers with high blood viscosity: a randomized, double-blind, placebo-controlled trial. Exp Gerontol. 2015;62:14-22.
Elevated blood viscosity is a risk factor for cardiovascular disease (CVD). Yerba maté (Ilex paraguariensis, Aquifoliaceae) tea, a popular South American beverage made from the leaves, has been found to have lipid-lowering effects, antioxidant activity, and other potential cardiovascular benefits. There were, however, no clinical studies that evaluated the effects of yerba maté tea on blood viscosity. So, the aim of this randomized, double-blind, placebo-controlled study was to evaluate the effects of yerba maté tea on blood viscosity, microcirculatory parameters, and other CVD risk factors in subjects with high blood viscosity.
Subjects (25-60 years old) were recruited from the Medical Examination Center of Shandong Hospital of Integrated Traditional Chinese and Western Medicine in Jinan, China. Subjects were included in the study if they had high blood viscosity and abnormal nailfold capillary images (an indicator of abnormal microcirculation). Subjects with cancer or other health conditions were excluded from the study.
Participants were randomly assigned to receive either yerba maté tea (Nobleza Gaucha; Misiones, Argentina [cited in the article as the “Molienda Company”]) or a placebo tea consisting of fried wheat* (Triticum aestivum, Poaceae). Subjects in both the yerba maté and placebo groups were instructed to steep one 5-g tea bag** five different times per day, each time in 300 mL of hot water.
At baseline, demographic information, body measurements, food intake, nailfold microcirculation data, and hemorheological measurements (blood flow properties) were recorded. Fasting blood samples and nailfold capillary images were obtained before and after the six-week treatment period. Information on biochemical parameters, blood viscosity, and lipid profiles were obtained from all the blood samples.
Out of the 234 individuals recruited for the trial, 142 completed the study. (Thirty-eight chose not to participate, 28 declined for “other reasons,” and 13 participants in each treatment group were lost to follow-up.) There were no significant differences between the two groups for any of the baseline characteristics evaluated.
Based on the nailfold capillary images, it was found that all microcirculatory parameters, with the exception of the length of the capillary loop, were significantly improved in the yerba maté tea group by the end of the study. In particular, blood flow was significantly increased (P < 0.01), and the capillary diameters evaluated were significantly decreased (P < 0.01) in comparison to baseline values. No significant effects were observed in the placebo group. Morphological, periphery capillary loop, and overall nailfold integrals were significantly reduced after six weeks in the yerba maté group (P < 0.01), but not in the placebo group. Treatment with yerba maté resulted in microcirculatory values in the normal or nearly normal range.
All blood viscosity parameters, including the equation K value of erythrocyte sedimentation rate (ESRK [inflammatory activity in the body can cause red blood cells (erythrocytes) to become more dense and settle more quickly]), whole blood viscosity, and plasma viscosity, were significantly reduced in the yerba maté group by the end of the study (P < 0.01) and were not statistically different from normal values. There were no significant effects found in the placebo group. In the yerba maté group, the vasodilator 6-keto prostaglandin F1α (6-keto-PGF1α) and the vasoconstrictor thromboxane B2 (TXB2) were significantly increased (P < 0.01) and decreased (P < 0.05), respectively, in comparison to baseline values. Consumption of yerba maté tea resulted in normal or nearly normal blood viscosity values. The placebo group was not significantly affected in this study.
At the end of the six-week study period, the yerba maté group had significantly increased high-density lipoprotein cholesterol (HDL-C; P < 0.00) as well as significantly decreased low-density lipoprotein cholesterol (LDL-C; P < 0.00), triglycerides (P < 0.00), and total cholesterol (P < 0.05), in comparison to baseline values. Lipid profiles improved in the yerba maté group to levels in normal untreated subjects. No significant changes were observed in the placebo group.
Subjects that participated in this study had high blood viscosity and microcirculation dysfunction. The fact that both of these health parameters improved and normalized in the yerba maté group, in addition to improvements in lipid profiles and biochemical parameters, suggests that this traditional South American beverage may help prevent the development of CVD and potentially reduce CVD mortality. However, this study had several limitations. The authors indicate that longer study periods are needed to confirm yerba maté’s effects on CVD risk factors. Future studies evaluating the cardiovascular benefits of yerba maté should include subjects with a range of additional risk factors and types of CVD, report potential adverse side effects, and ensure that inactive placebos are used.
—Laura M. Bystrom, PhD
* Whole grains such as wheat are known to impact certain cardiovascular health parameters.1,2 It is possible that the wheat placebo may have had an effect on blood viscosity, although it did not appear to in this trial.
** Previous clinical studies of yerba maté have used dosage regimens of 50 g/day of “green” yerba maté (commercial yerba maté similar to what was used by Yu et al.) or 20 g/day of roasted yerba maté, which represent typical levels of yerba maté consumed by the populations of South American countries. Yu et al. used 5 g/day, a 4- to 10-fold lower dose of yerba mate, yet the results of this paper suggest greater improvements in serum lipid profiles than what has been reported in other clinical studies using higher dosages. The possible reasons for this discrepancy are not described in the article.
- Sinclair SE, Mansfield ED, Wells GA. Evidence for a whole grains and coronary heart disease health claim. International Food Risk Analysis Journal. 2013;3(1):1-25. Available at: http://cdn.intechopen.com/pdfs-wm/43251.pdf. Accessed January 19, 2016.
- Truswell AS. Cereal grains and coronary heart disease. European Journal of Clinical Nutrition. 2002;56(1):1-14. Available at: www.nature.com/ejcn/journal/v56/n1/full/1601283a.html. Accessed January 19, 2016.