This member of the Aster family has a long history of native use in Paraguay as a sweetener for teas and foods. It contains a substance known as stevioside that is 100 to 300 times sweeter than sugar, but provides no calories.1

In the early 1970s, a consortium of Japanese food manufacturers developed stevia extracts for use as a zero-calorie sugar substitute. Subsequently, stevia extracts became a common ingredient in Asian soft drinks, desserts, chewing gum, and many other food products. Extensive Japanese research has found stevia to be extremely safe. However, there have not been enough US studies for the FDA to approve stevia as a sugar substitute. Without identifying it as such, stevia is nonetheless widely used by savvy manufacturers to sweeten commercial beverage teas and other products.

Although stevia is best known as a sweetener, when stevia extracts are taken in very high doses they may reduce blood pressure, according to two large Chinese studies.

What Is Stevia Used for Today?

Stevia is primarily useful as a sweetening agent. In addition, two double-blind studies suggest that it may also offer potential benefits for hypertension.3,10

Very weak evidence hints at potential benefits in diabetes.5

What Is the Scientific Evidence for Stevia?

Hypertension

A 1-year, double-blind, placebo-controlled study of 106 individuals with high blood pressure evaluated the potential benefits of stevia for reducing blood pressure.4 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).10 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.11

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.12 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.13

Dosage

Stevia is sold as a powder to be added to foods as needed for appropriate sweetening effects. It tastes slightly bitter if placed directly in the mouth. In liquids, though, this is generally not noticeable, and most people find the taste delightfully unique.

In the studies showing an effect on blood pressure, stevia was given as a standardized extract supplying 250-500 mg of stevioside 3 times daily (a dose considerably higher than any reasonable use of stevia as a sweetener).

Safety Issues

Animal tests and the extensive Japanese experience with stevia suggest that this is a safe herb.5,6 Based primarily on the apparently incorrect belief that stevia has been used traditionally to prevent pregnancy,5 some researchers have expressed concern that stevia might have an antifertility effect in men or women. However, evidence from most (though not all) animal studies suggests that this is not a concern at normal doses.7-9

The two studies described above in which use of very high dosages of a stevia extract led to reductions in blood pressure raise at least theoretical concerns about stevia's safety. In theory, the herb could excessively reduce blood pressure in some people. Furthermore, if stevia can reduce blood pressure, that means that it is, in some fashion, acting on the cardiovascular system.

Since sugar substitutes are meant to be consumed in essentially unlimited quantities by a very wide variety of people, the highest levels of safety standards are appropriate, and unknown effects on the heart and blood circulation are potentially worrisome. This concern is somewhat mitigated by the fact that the daily dose of stevioside used in those studies was considerably higher than is likely to be consumed if whole stevia is used for sweetening purposes. Reassurance also comes from the study that found no effect with a dose of 15 mg/kg per day.

Safety in young children, pregnant or nursing women, or those with severe liver or kidney disease has not been conclusively established. Because of the concerns raised in the previous paragraph, individuals with cardiovascular disease should use high doses of stevia extracts only under physician supervision.