study of 106 individuals with
high blood pressure
evaluated the potential benefits of stevia for reducing blood pressure.
In the treated group, the average blood pressure at the beginning of the study was about 166/102. Participants were given either placebo or stevioside (stevia extract) at a dose of 250 mg 3 times daily. By the end of the study, the average blood pressure had fallen to 153/90, a substantial if not quite adequate improvement. Note that this is a high dose of steviosides, the sweetness equivalent of more than 1/3 of a pound of sugar daily!
However, this study is notable for finding no benefits at all in the placebo group. This is unusual and tends to cast doubt on the results.
Benefits were also seen in a 2-year, double-blind, placebo-controlled study of 174 people with mild hypertension (average initial blood pressure of approximately 150/95).
This study, performed by some of the same researchers, used twice the dose of the previous study: 500 mg 3 times daily. A reduction in blood pressure of approximately 6%-7% was seen in the treatment group as compared to the placebo group, beginning within 1 week and enduring throughout the entire 2 years. At the end of the study, 34% of those in the placebo group showed heart damage from high blood pressure (left ventricular hypertrophy), while only 11.5% of the stevioside group did, a difference that was statistically significant. No significant adverse effects were seen.
However, once again, no benefits at all were seen in the placebo group. This is a red flag for problems in study design. Both studies were performed in China, a country that has a documented history of questionable medical study results.
Furthermore, a study by an independent set of researchers failed to replicate these findings. In this study, stevioside was given according to body weight, at a dose of 3.75 mg/kg per day, 7.5 gm/kg per day, or 15 mg/kg per day.
Compared to placebo, none of these doses affected the blood pressure of the study participants, all of whom had mild high blood pressure. These finding do not entirely refute those above, however, as the dosage of stevia used was somewhat on the low side. For example, for a man weighing 60 kg (132 lbs), the highest dose would be 300 mg 3 times a day.
Another study involving diabetics as well as healthy subjects found that stevia, at a dose of 250 mg 3 times daily, had no significant effect on blood pressure after 3 months of treatment.