In 2009, FDA considered "Rebiana (rebaudioside A) to be Generally Recognized As Safe (GRAS)".[49][50] The report includes a detailed list of international studies, references, and chemical analysis.[49]
Two 2010 review studies found no health concerns with stevia or its sweetening extracts.[51][52] In addition, a 2009 review study found that stevioside and related compounds have anti-hyperglycemic, anti-hypertensive, anti-inflammatory, anti-tumor, anti-diarrheal, diuretic, and immunomodulatory actions.[53]
The European Food Safety Authority evaluated the safety of steviol glycosides, extracted from the leaves of the Stevia rebaudiana Bertoni plant, as sweetener and expressed its opinion on 10 March 2010. The Authority established an Acceptable Daily Intake (ADI) for steviol glycosides, expressed as steviol equivalents, of 4 mg/kg bodyweight/day. On 11 November 2011, the European Commission allowed the usage of steviol glycosides as a food additive, establishing maximum content levels for different types of foods and beverages.[54]
Preliminary human studies suggest stevia may affect blood pressure,[55] although another study has shown it to have no effect on hypertension.[56] Indeed, millions of Japanese have been using stevia for over thirty years with no reported or known harmful effects.[57] Similarly, stevia leaves have been used for centuries in South America, spanning multiple generations in ethnomedical tradition as a treatment for diabetes mellitus type 2.[58]
In 2006, the World Health Organization (WHO) evaluated experimental studies of stevioside and steviols conducted on animals and humans, and concluded "stevioside and rebaudioside A are not genotoxic in vitro or in vivo and that the genotoxicity of steviol and some of its oxidative derivatives in vitro is not expressed in vivo."[59] The report also found no evidence of carcinogenic activity. Furthermore, the report noted "stevioside has shown some evidence of pharmacological effects in patients with hypertension or with diabetes mellitus type 2",[59] but concluded further study was required to determine proper dosage. The WHO's Joint Experts Committee on Food Additives has approved, based on long-term studies, an acceptable daily intake of steviol glycoside of up to 4 milligrams per kilogram of body weight.[60]
A 1985 study reported that steviol, a breakdown product from stevioside and rebaudioside (two of the sweet steviol glycosides in the stevia leaf), is a mutagen in the presence of a liver extract of rats pretreated with a PCB blend[61] � but this finding was criticized.[62] Over the following years, bioassay, cell culture, and animal studies have shown mixed results in terms of toxicology and adverse effects of stevia constituents. While reports emerged that found steviol and stevioside to be weak mutagens,[63][64] the bulk of studies show an absence of harmful effects.[65][66] In a 2008 review, 14 of 16 studies cited showed no genotoxic activity for stevioside, 11 of 15 studies showed no genotoxic activity for steviol, and no studies showed genotoxicity for rebaudioside A. No evidence for stevia constituents causing cancer or birth defects has been found.[65][66]
In relation to diabetes, studies have shown stevia to have a possible trophic effect on β-cells of pancreas,[14] to improve insulin sensitivity in rats,[67] and possibly even to promote additional insulin production,[68] helping to reverse diabetes and metabolic syndrome.[69] Stevia consumed before meals significantly reduced postprandial insulin levels compared to both aspartame and sucrose.[70] A 2011 review study concluded that stevia sweeteners would likely benefit diabetic patients.[51]
http://en.wikipedia.org/wiki/Stevia