Vol. 7(46), pp. 3343-3353, 10 December, 2013 DOI: 10.5897/JMPR2013.5276 ISSN 1996-0875 ©2013 Academic Journals http://www.academicjournals.org/JMPR Journal of Medicinal Plants Research Review Nutritional and therapeutic values of Stevia rebaudiana: A review Ena Gupta1, Shalini Purwar1, Shanthy Sundaram1* and G. K. Rai2 1 Centre for Biotechnology, University of Allahabad, Uttar Pradesh, India. Centre of Food Technology, University of Allahabad, Uttar Pradesh, India. 2 Accepted 12 November, 2013 Stevia rebaudiana is a nutrient rich natural sweetest plant of Asteraceae family. The leaves naturally contain diterpene glycosides stevioside, rebaudiosides A-F, steviolbioside and dulcoside, which are responsible for its sweet taste and have commercial value all over the world as sugar substitute in foods, beverages or medicines. It is a magical plant which offers sweetness with fewer calories and do not show any side effects after consumption on human health. Stevia has many pharmacological and therapeutic applications as suggested by many preclinical and some clinical studies; these are nontoxic and possess antioxidant, antimicrobial, antifungal and anticarcinogenic activity. In future Stevia is likely to become a major source of high potency low calorie sweetener for growing natural food market. This review article presents beneficial role of Stevia and its metabolites on health promoting properties. Key words: Stevia rebaudiana, steviosides, sweetner. INTRODUCTION Stevia rebaudiana (Bertoni) is an herb of the 950 genera of Asteraceae family. Centuries ago, Paraguay natives used the leaves of this small, herbaceous, semi-bushy, perennial shrub to sweeten their bitter drinks. Gaurani Indians extensively used this plant for more than 1500 years. Dr. Moises Santiago Bertoni discovered this plant in 1888 at Paraguay. In 1905, the plant was scientifically named as S. rebaudiana after a Paraguayan chemist Dr. Rebaudi. It was reported that there are around 150 species within the Stevia family including Stevia dianthoidea, Stevia Phlebophylla, Stevia anisostemma, Stevia bertholdii, Stevia crenata, Stevia enigmatica, Stevia eupatoria, Stevia lemmonii, Stevia micrantha, Stevia ovata, Stevia plummerae, S. rebaudiana, Stevia salicifolia, Stevia serrata and Stevia viscida with all plants being sweet but rebaudiana having the highest sweetness levels. It is also known as sweet herb, sweet leaf, honey leaf, candy leaf and honey yerba (Carakostas et al., 2008). Originating in the South American wild, it could be found growing in semi-arid habitat ranging from grassland to scrub forest to mountain terrain. When cultivated or growing naturally in fertile soil, the mature Stevia plant grows up to 65 cm (26 inches) to as tall as 180 cm (72 inches). It is a short day plant and flowering from January to March in the southern hemisphere. The flowers are white in color with a pale purple throat. They are small in size and arranged in the form of small corymbs (Goettemoeller and Ching, 1999; Singh and Rao, 2005). It prefers a sandy soil, requiring a warm sunny position. The suitable natural climate is semihumid subtropical with temperature extremes from 21 to 43°C and average 24°C (Huxley, 1992). It is widely used in many parts of the world as sweetener and grown commercially in Central America, Korea, Paraguay, *Corresponding author. E-mail: shanthy_s@rediffmail.com. Tel: +919956359786. 3344 J. Med. Plants Res. Brazil, Thailand and China (Mizutani and Tanaka, 2002; Kim et al., 2002, Jaroslav et al., 2006). Two French chemists in 1931 isolated the glycosides which is secondary metabolites responsible for the sweet taste of Stevia (Bridel and Lavielle, 1931). The chemical structure was established in 1952 as a diterpene glycoside. The leaves of Stevia contain a natural complex mixture of eight sweet diterpene glycosides, including isosteviol, stevioside, rebaudiosides (A, B, C, D, E, F), steviolbioside and dulcoside A (Rajasekaran et al., 2008; Goyal et al., 2010). Out of various steviol glycosides (SGs), stevioside and rebaudioside A are the major metabolites and these compounds are 250 to 300 times as sweet as sucrose (Allam et al., 2001; Mantovaneli et al., 2004; Debnath, 2008), pH-stable, heat-stable, not fermentable (Abdullateef and Osman, 2012) and posses health promoting potential. Along with sweetness, Stevia has some bitter aftertaste due to the presence of some essential oils, tannins and flavonoids (Phillips, 1987). The Stevia leaves have sensory and functional properties superior to those of many other high-potency sweeteners and is likely to become a major source of natural sweetener for the growing food market (Goyal et al., 2010). It is commercially well known to exert beneficial effects on human health and has become an interesting area of research these days. Leaves of S. rebaudiana has many medical applications like antimicrobial (Satishkumar et al., 2008), antiviral (Kedik et al., 2009), antifungal (Silva et al., 2008), anti-hypertensive (Chan et al., 1998; Lee et al., 2001; Hsieh et al., 2003), anti-hyperglycaemic (Jeppesen et al., 2002; Benford et al., 2006), anti-tumour (Satishkumar et al., 2008), antiinflammatory, anti-diarrhoeal, diuretic, anti-human rotavirus activities (Das et al., 1992; Takahashi et al., 2001), anti-HIV (Takahashi et al., 1998), hepatoprotective (Mohan and Robert, 2009) and immunomodulatory effects (Jaroslav et al., 2006; Chatsudthipong and Muanprasat, 2009). Toxicological studies have shown that secondary metabolites present in Stevia does not have teratogenic, mutagenic or carcinogenic effects and no allergic reactions have been observed after consuming it as an sweetener (Pol et al., 2007). The objective of this article is to review systematic literature and to summarize the nutritional, pharmacological and therapeutic applications of S. rebaudiana and its related compounds. (SGs) are metabolized and eliminated through similar pathways in both humans and animals, has been studied by Genus et al. (2003, 2007). Rebaudioside A in the digestive tract is first metabolized by microbes in the colon to stevioside which is further converted into glucose molecule and steviol. The released glucose molecule is used by the bacteria in the colon and is not absorbed into the blood stream. The metabolized components essentially leave the body and there is no accumulation. The metabolism of steviol glycosides to steviol means that the metabolic equivalency of the different steviol glycosides permits to apply the findings from studies with stevioside to the safety evaluation of rebaudioside A, and thus to the safety of Stevia (Koyama et al., 2003). There Stevia species possess some differences between, it has been demonstrated that the conversion rate of rebaudiside A and stevioside are similar between rats and humans, with the conversion from stevioside to steviol more rapid than that of rebaudioside A to stevioside in both species. Moreover, quantitative and qualitative similarities have been found between the organisms in the gut (microflora) of rat and the human body (Wingard et al., 1980). A study on the human digestive tract demonstrates that steviol is not altered or changed at either high or low concentrations as observed through human faeces, indicating that steviol is in fact the final product of Stevia metabolism (Koyama et al., 2003). The study also showed that the majority of steviol glycosides are absorbed and glucuronidated (a bond intended to help them clear out of the blood) in the liver. The newly bonded glucuronide is released in the blood and filtered by the kidneys into the urine. Small amounts of glucuronidate that remain in the colon are excreted through fecal matter. Tests with stevioside compounds and the effect of gastric juices and digestive enzymes on them show their failure to degrade or rearrange the compounds (Wingard et al., 1980). In vitro digestibility of steviosides by various digestive enzymes was examined by Hutapea et al. (1997), it was found that none of the enzymes digested the stevioside and intestinal microflora hydrolyzed it to both steviol and steviol-16, 17 alphaepoxide. Later, steviol 16, 17 alpha-epoxide was then completely converted back into steviol, which further excreted from the body in urine as steviol glucuronide (Chatsudthipong and Muanprasat, 2009). ACCEPTABLE DAILY INTAKE (ADI) METABOLISM S. rebaudiana leaves contain a zero-calorie ent-kaurene diterpene glycosides (stevioside and the rebaudiosides) 300 times sweeter than sucrose with superior solubility in water and a positive taste profile that are safely metabolized by the body without any effect (Soejarto et al., 1982; Megeji et al., 2005; 5. Geuns et al., 2007). The major compounds of Stevia as steviol glycosides Globally, scientists have concluded that Stevia sweeteners are safe for people of all ages. Stevia leaf or extracted forms like stevioside, rebaudioside A and steviol glycosides was approved by US FDA as a dietary supplement considered (Generally recognized as safe) rating in the US (GRAS Notification 287 for Steviol Glycosides with Rebaudioside A and Stevioside as Principal Components) as appears to have an adequate Gupta et al. daily intake (ADI) of 25 mg/kg (Genus et al., 2003) (following 100-fold safety factor, commonly seen in ADI values) in rats which is around 7.9 mg/kg in humans. Xili et al. (1992) also calculated the acceptable daily intake (ADI) of stevioside which is 7.9 mg/kg body weight. However, this ADI should be considered as a minimum value as the authors did not test concentrations of stevioside higher than 793 mg/kg body weight. The routine daily human consumption of 5 to 6 mg of Stevia leaf extract as a dietary sweetener per kg of body weight is safe (Carakostas et al., 2008). Rebaudioside-A has been used for years throughout the world as a natural non-nutritive sweetening alternative to sucrose and other nutritive variants (Goyal et al., 2010). The Dietary Supplement Health and Education Act (DSHEA) passed in the United States in 1994 were also approved steviol glycosides (SGs) to be used as a functional ingredient in dietary supplements (Williams and Burdock, 2009). Minutes of the Tenth Meeting of Food Authority held on 20th September, 2012 at 11:00 h at FDA Bhavan, New Delhi approved the use of steviol glycoside as an artificial sweetener in various foods. Currently, The Joint FAO/WHO Expert Committee on Food Additives (JECFA) conducted a thorough scientific review of all the available scientific data and concluded Stevia sweeteners are safe for use in foods and beverages, an acceptable daily intake of steviol glycoside of up to 4 mg/kg of body weight was recommended. The European Food Safety Authority (EFSA) in 2010 assessed the safety of steviol glycosides from Stevia and established an Acceptable Daily Intake (ADI) for their safe use. Daily Intake (ADI) of 4 mg/kg body weight is expressed as steviol equivalents (Carakostas et al., 2008). The ADI is listed in units of mg per kg of body weight.‖ The European Commission on 11th November 2011, allowed the usage of steviol glycosides as a food additive which will probably lead to wide-scale use in Europe (Stoyanova et al., 2011). COMPOSITION A number of natural products have been isolated from S. rebaudiana Bertoni, more than 100 compounds have been identified from this species, the best known are steviol (ent-13-hydroxykaur-16-en-19-oic acid and its glycosides) and its glycosides stevioside, rebaudioside AF, steviolbioside, dihydroisosteviol, rubusoside and dulcoside A. Savita et al. (2004) analysed the leaves of S. rebaudiana on dry weight basis and calculated the energy value of 2.7 kcal g-1. Structurally, stevioside (13[2-O-ß Dglucopyranosyl-X-glucopyran-osyl) oxy] kaur-16en-19- oic-acid ß-D- glucopyranosyl ester) is a glycoside with a glucosyl and a sophorosyl residue attached to the aglycone steviol, which has a cyclopentanon hydrophenanthrene skeleton. Stevia is a nutrient rich herb containing substantial amount of other nutrients, like 3345 80 to 85% water, protein, fibre, aminoacids, free sugars, iminosugar steviamine and its (-)-steviamine enantiomer, lipids, essential oils, ascorbic acid, beta carotene, riboflavin, thiamine, austroinulin, sterebins A-H, nilacin, rebaudi oxides, gibberellic acid, indole-3-acetonitrile, apigenin, quercetin, isoquercitrin, luteolin, miocene, kaempferol, stigmasterol, xanthophyllus, umbeliferone, chlorogenic acid, caffeic acid, dicaffeoylquinic acid, chromium, cobalt, magnesium, iron, potassium, phosphorus and trace elements (Komissarenko et al., 1994; Choudhary and Bandyopadhyay, 1999; Konoshima and Takasaki, 2002; Sharma et al., 2006; Jayaraman et al., 2008; Esmat and Ferial, 2009; Hu et al., 2010). The nutritional profiles of the leaves of S. rebaudiana are shown in Tables 1 to 8. THERAPEUTIC VALUES OF S. REBAUDIANA The ancient Ayurvedic system of medicine has a long history regarding the use of S. rebaudiana (Megeji et al., 2005). Leaves of S. rebaudiana has been recommended as a treatment against various chronic and non-chronic diseases like diabetes, cardiovascular disease, cancer, renal disease, obesity, inflammatory bowel disease and dental caries. Glucoregulation Diabetes mellitus (DM) is a group of diseases characterized by hyperglycemia and varying degrees of an insufficient insulin effect. According to the World Health Organization (WHO, 2004), there are approximately 177 million people with diabetes worldwide. The global prevalence of diabetes will go up from 8.6% in 2012 to 9.8% in 2030 and the numbers of people affected with diabetes will go up from 285 to 435 million. India leads the world with the largest number of diabetic subjects, earning the dubious distinction of being termed the ―diabetes capital of the world‖. Stevia leaf extract has been used traditionally in the treatment of diabetes (Megeji et al., 2005; Soejarto et al., 1982). Their ingestion causes a slight suppression of plasma glucose levels and significantly increased glucose tolerance in normal adult humans (Curi et al., 1986). Steviol glycosides have an enhancing effect on insulin secretion by directly acting on β-cells without altering the + K - ATP channel activity and cAMP level in the islets, thus documenting stevioside and steviol as potent antihyperglycemic agents (Jeppesen et al., 2000). Stevioside regulate blood glucose levels by enhancing not only insulin secretion, but also insulin utilization in insulin-deficient rats; which was due to decreased phosphoenolpyruvate carboxykinase (PEPCK) gene expression in rat liver by stevioside's action of slowing down gluconeogenesis suggested by Chen et al. (2005). Study conducted in diabetic humans, where a single acute dose of stevioside (1,000 mg) was able to reduce 3346 J. Med. Plants Res. Table 1. Amount of sweet glycosides in Stevia rebaudiana leaves (% of the leaves dry weight). Stevioside Steviol Steviolbioside Rebaudioside A Kinghorn and Soejarto (1985) 5-10 ND ND 2-4 RebaudiosideB Rebaudioside C Rebaudioside D Dulcoside A ND 1-2 ND 0.4-0.7 Glycoside Crammer and Ikan (1987) 3-10 ND ND 1.0 Reference Gardana Kolb et al. et al. (2001) (2010) 3.78-9.75 5.8 ND ND ND ND 1.62-7.27 1.8 ND ND ND 0.2 ND ND ND ND Goyal et al. (2010) 9.1 ND ND 3.8 Atteh et al. (2011) 6.5 ND ND 2.3 Jaworska et al. (2012) 2.0 0.70 1.2 5.0 ND 0.6 ND 0.3 ND ND ND ND 0.50 2.0 3.3 1.0 ND 1.3 ND ND Table 2. Proximate analysis of dried Stevia rebaudiana leaves (g 100 g_1 dry weight basis). Reference Component Tadhani and Subhash (2006) Goyal et al. (2010) Kaushik et al. (2010) Mishra et al. (2010) Serio (2010) Abou-Arab et al. (2010) Atteh et al. (2011) Moisture Protein Fat Ash ND 20.4 4.34 13.1 4.65 11.2 1.9 6.3 7.7 12 2.7 8.4 7 10 3 11 ND 11.2 5.6 ND 5.37 11.40 3.73 7.41 ND 16.0 2.6 15.5 Carbohydrate 35.2 ND ND 52 53 61.9 ND Crude fibre ND 15.2 ND 18 15 15.5 6.8 Table 3. Fatty acid composition of Stevia rebaudiana leaf oil (g 100 g_1). Fatty acids Palmitic acid (C16) Palmitoleic acid (C16-1) Stearic acid (C18) Oleic acid (C18-1) Linoleic acid (C18-2) Linolenic acid (C18-3) Reference Tadhani and Subhash (2006) Atteh et al. (2011) 27.51 29.5 1.27 3.0 1.18 4.0 4.36 9.9 12.40 16.8 21.59 36.2 the postprandial area under the curve (AUC) of glucose by 18% relative to control (1 g corn starch) and appeared to benefit the insulin:glucose ratio in serum by 40% (Gregersen et al., 2004). The medicative effects of medium-polar (benzene:acetone, 1:1 v/v) extract of leaves from S. rebaudiana (family Asteraceae) on alloxan-induced diabetic rats was studied. Medium-polar leaf extract of S. rebaudiana (200 and 400 mg/kg) produced a delayed but significant (P < 0.01) decrease in the blood glucose level, without producing condition of hypoglycemia after treatment, together with lesser loss in the body weight as compared with standard positive control drug glibenclamide (Misra et al., 2011). Stevioside also enhances glucose-stimulated insulin secretion, but does not affect fasting insulinemia (Xiao and Hermansen, 2005; Chen et al., 2006). In a 6-week study, steviosidefed diabetic rats displayed significantly enhanced firstphase insulin responses with concomitant suppression of glucagon secretion and attenuation of blood glucose concentration excursions (Jeppesen et al., 2003). The effects of Stevia leaves and its extracted polyphenols and fiber on streptozotocin induced diabetic rats were studied Gupta et al. 3347 Table 4. Amino acid composition of Stevia rebaudiana leaves (g 100 g_1 dry matter). Amino acids Essential amino acid Arginine Lysine Histidine Phenyl alanine Leucine Methinine Valine Threonine Isoleucine Reference Abou-Arab et al. (2010) 0.45 0.70 1.13 0.77 0.98 1.45 0.64 1.13 0.42 Non-essential amino acid Aspartate Serine Glutamic Proline Glycine Alanine Cysteine Tyrosine 0.37 0.46 0.43 0.17 0.25 0.56 0.40 1.08 Li et al. (2011) 0.81 0.15 0.34 0.88 1.30 ND 0.94 0.75 0.72 1.72 1.02 1.90 1.72 0.85 0.95 ND 0.49 Table 5. Minerals content of dried Stevia rebaudiana leaves (mg 100 g_1). Component/ Mineral Calcium Phosphorus Sodium Potassium Iron Magnesium Zinc Tadhani and Subhash (2006) 1550 350 160 2510 36.3 ND 6.39 Goyal et al. (2010) 544 318 89.2 1780 3.9 349 1.5 Reference Kaushik et Mishra et al. (2010) al. (2010) 722 464.4 ND 11.4 32.7 190 839 1800 31.1 55.3 ND 349 ND 1.5 Table 6. Water-soluble vitamins of Stevia rebaudiana leaves (mg/100 g dry base of extract). Vitamins Vitamin C Vitamin B2 Vitamin B6 Folic acid Niacin Thiamine Reference Kim et al. (2011) 14.97 0.43 0.00 52.18 0.00 0.00 and found that Stevia leaves have a significant role in alleviating damage in the streptozotocin-diabetic rats Serio (2010) 600 318 ND 1800 3.9 500 ND Abou-Arab et al. (2010) 17.7 ND 14.93 21.15 5.89 3.26 1.26 Atteh et al. (2011) 8.2 2.6 0.7 17.3 366 2.4 20 besides its hypoglycemic effect and it also reduce the risk of oxidative stress (Shivanna et al., 2013). Overall, Stevia possess the ability to increase the insulin effect on cell membranes, increase insulin production, stabilize glucagon secretion and blood sugar levels, and improve glucose tolerance to ingested carbohydrates and lower post-prandial blood sugar levels in both animals and humans. In other words, Stevia is shown to provide a comprehensive set of mechanisms that counter the mechanics of type II diabetes and its eventual complications. Thus, sugars can be replaced with steviol glycosides or stevioside of Stevia leaf to support healthy glucoregulation. The addition of leaves of Stevia, dried or in powder form in supplementary food products of diabetic patients aid in increasing the natural sweetness and also help in rejuvenating the pancreatic gland. 3348 J. Med. Plants Res. Blood pressure regulation ―Essential hypertension‖ is defined as an increase in blood pressure above certain measured levels. The definition of high blood pressure begins at a systolic blood pressure of 140 mmHg and a diastolic blood pressure of 90 mmHg. High blood pressure results in pathological changes accrue in medium sized and small arteries that cause further increases in blood pressure. The pathology is a thickening of the walls of these blood vessels so that effectively the diameter of the vessels is diminished. This causes the heart to work harder to pump enough blood to meet the demands of all the tissues increasing the risk for to heart attack or stroke. Stevia can be used as a heart tonic to normalize blood pressure levels, to regulate heartbeat, and for other cardiopulmonary indications. In humans, a hot water extract of the leaf has been shown to lower both systolic and diastolic blood pressure. Studies on Stevia extracts, as well as its isolated glycosides, demonstrate its hypotensive and diuretic action. Stevia acts at the cell membrane level much in the same way as a type of medication known as a calcium channel blocking agent. These medicines are routinely prescribed to help control high blood pressure by relaxing the muscular walls of the arteries causing the elevation in blood pressure. Studies suggest that Stevia acts to relax arteries and lower blood pressure. Leaves of S. rebaudiana contain non-caloric sweeteners (steviol glycosides) whose consumption could exert beneficial effects on human health (Gardana et al., 2010). Glycosides present in Stevia possess valuable biological properties. Regular consumption of these compounds decreases the content of cholesterol in the blood (Atteh et al., 2008), improves cell regeneration and blood coagulation, suppresses neoplastic growth and strengthens blood vessels (Barriocanal et al., 2008; Jeppesen et al., 2003; Maki et al., 2008; Wingard et al., 1980). The use of stevioside results in a clinically significant hypotensive effect in spontaneously hypertensive rats, without adversely affecting their heart rates or serum catecholamine levels (Chan et al., 1998). Phytosterols present in the wax of Stevia leaves were found to respond against cardiovascular defects (Markovie et al., 2008). Stevioside induces vasorelaxation (Lee et al., 2001; Wong et al., 2004; Liu et al., 2003). This effect was tested in a year-long randomized, double-blind, placebocontrolled study of 106 hypertensive subjects who consumed capsules containing either stevioside (750 mg daily) or placebo (Chan et al., 2000). Beginning after 3 months and persisting throughout the remaining 9 months of the study, the subjects consuming stevioside exhibited significantly greater decreases in systolic and diastolic blood pressures. No significant adverse effects occurred. In a longer 2-year study, compared to placebo, 1,500 mg of stevioside daily also produced significantly greater decreases in systolic and diastolic blood pressures in subjects with mild hypertension (Hsieh et al., 2003). Studies have shown that purified stevioside induces hypotension, diuresis, and natriuresis in rats and these effects are probably related to changes in prostaglandin activity (Melis et al., 1985). The effect of consumption of Stevia extract on 20 selected hypercholesterolemic women was studied and it was found that consumption of 20 ml extract in a glass of water (200 ml) helps in the reduction of bad cholesterol such as triglyceride and low-density lipoprotein (LDL) with significant increase in good cholesterol that is highdensity lipoprotein (HDL), and it was concluded that Stevia extract had a hypolipidaemic effect and it maintains cardiovascular health (Sharma and Mogre, 2007). The previous studies prove the clinical efficacy of Stevia leaves in reducing chronic hypertension by relaxing arteries and help prevent the build up of calcium on artery walls. Cancer Cancer can be regarded as a disease of the body’s cells. Its development involves damage to the DNA of the cells and this damage accumulates overtime. Stevia and its metabolites have been used for years throughout the world as a natural non-nutritive sweetening alternative to sucrose and other nutritive variants (Goyal et al., 2010). In addition, the toxicity of Stevia has been investigated extensively in both short- and long-term studies. Importantly, no serious toxic, genotoxic, or carcinogenic effects were detected in mammalian species and it is safe for human consumption (Aze et al., 1991; Toyoda et al., 1997). Labdane sclareol, compound present in leaf extract of Stevia has anti-tumorous and cytotoxic properties (Kaushik et al., 2010). Studies have demonstrated the inhibitory effects of Stevia leaf extracts and their polyphenolic constituents on tumor promotion and initiation. Stevioside, the Stevia leaf aglycones, steviol and isosteviol, and their metabolites have been reported to inhibit tumor promotion by blocking Epstein-Barr virus early antigen (EBV-EA) induction (Akihisa et al., 2004) as well as by reducing tumor formation in the two-stage mouse skin carcinogenesis model following sequential exposure to 7,12-dimethylbenz [a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) (Konoshima and Takasaki, 2002; Yasukawa et al., 2002; Takasaki et al., 2009). The hydrolysis product of stevioside, isosteviol, potently inhibits DNA replication and human cancer cell growth in vitro (with LD50 values of 84 to 167 μMol) (Mizushina et al., 2005). The toxicity of rebaudioside-A was studied by bacterial reverse mutation test (Ames test) using standard Salmonella typhimurium as well as Escherichia coli, there was no statistically significant increase in the number of relevant colonies Gupta et al. exposed to rebaudioside-A at concentrations up to 5000 μg/plate. In the Ames test, rebaudioside-A was found to be non-mutagenic in these two bacterial strains. Rebaudioside-A was evaluated for mutagenic potential in cultured human lymphocytes, this test did not induce a statistically significant increase in the incidence of chromosomal aberrations or polyploidy in cultured Chinese Hamster V79 cells after 4 and 20 h treatments at any of the doses tested with or without S9 metabolic activation. Additionally, rebaudioside-A was shown not to cause any signs of toxicity in male Wistar rats after being administered a single dose of 2000 mg/kg of body weight and observed for 16 h post dosing (Williams and Burdock, 2009). Effect of stevioside against tumor was examined and stevioside slowed the tumor promoting agent (TPA) induced tumor promotion in a skin carcinogenesis in mice (Nakamura et al., 1995). Toxic and carcinogenic effects of stevioside was studied on initiation and promotion of urinary bladder, results showed that pre-neoplastic or neoplastic lesions development was not enhanced in urinary bladders by stevioside while studies performed with the dose effect of bladder carcinogenicity of N-nitrosobutyl-N- (4-hydroxybutyl) amine (Hagiwara et al., 1984). Subsequently, no neoplastic or pre-neoplastic lesions were observed in any tissue (Xili et al., 1992). Steviol and stevioside were tested for mutagenicity in S. typhimurium strains TA98 and TA100 and for chromosomal effects on cultured human lymphocytes; results revealed that steviol did not exhibit mutagenicity in either TA98 or TA100, with or without metabolic activation. However, stevioside was not mutagenic at concentrations up to 25 mg/plate, but showed direct mutagenicity to only TA98 at 50 mg/plate. No significant chromosomal effect of stevioside and steviol was observed in cultured blood lymphocytes from healthy donors (Suttajit et al., 1993). Stevioside, a bioactive compound present in Stevia was found to be nonmutagenic in mutagenicity tests using bacteria (reverse mutation assay, forward mutation assay, umu test and rec assay), cultured mammalian cells (chromosomal aberration test and gene mutation assay) and mice (micronucleus test) (Matsui et al., 1996). The toxicological effects of low concentrations of stevioside on apoptosis induced by serum deprivation using the PC12 cell system was studied by using DNA electrophoresis and TUNEL signal assays and on the basis of data it was found that stevioside enhanced apoptosis induced by serum deprivation and this enhancement was caused by increased expression of Bax and of cytochrome c released into the cytosol which suggest that stevioside affects the regulation of the normal apoptotic condition (Takahashi et al., 2012). Renal function Globally, there are nearly 70 million people with kidney disease of varying severity levels. Chronic kidney disease 3349 resulted in 400,000 deaths in 1990 and 735,000 deaths in 2010 (Lozano, 2012). The kidneys are essential organs for maintaining many aspects of the internal environment of the body. The main function of kidney is to maintain homeostatic balance with respect to fluids, electrolytes, and organic solutes. Various disease conditions may affect the kidney and disturb the normal functioning of the nephrons. Melis (1992) studied the effect of stevioside from the leaves of S. rebaudiana on renal function of normal and hypertensive rats. Analysed stevioside acts as a typical systemic vasodilator which provoked hypotension, diuresis and natriuresis in both the normal and hypertensive rats. Constant administration of stevioside in both normal and hypertensive rats increase the glomerular filtration rate (GFR) and renal plasma flow (RPF) which was due to vasodilation of both the afferent and efferent arterioles. Study was designed to explore the direct effect of stevioside on transepithelial transport of p-aminohippurate (PAH) in isolated S2 segments of rabbit proximal renal tubules using in vitro microperfusion. Findings suggest that stevioside, at a pharmacological concentration of 0.70 mM, inhibits transepithelial transport of PAH by interfering with the basolateral entry step, the rate-limiting step for transepithelial transport. The lack of effect of stevioside on transepithelial transport of PAH on the luminal side and its reversible inhibitory effect on the basolateral side indicate that stevioside does not permanently change PAH transport and should not harm renal tubular function at normal human intake levels (Jutabha et al., 2000). Yuajit et al. (2013) studied the inhibitory effect and detailed mechanisms of steviol and its derivatives on cyst growth using a cyst model in Madin-Darby canine kidney (MDCK) cells. Results revealed that steviol retards MDCK cyst progression, first by directly inhibiting cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel activity and second by reducing CFTR expression, in part, by promoting proteasomal degradation of CFTR. Steviol and its analogs represent promising natural plant-based drug candidates for treatment of polycystic kidney disease. Obesity Obesity is the most common nutritional disorder; it is a state of excess accumulation of fat in the body. In clinical terms, obesity is a condition of excess body weight more than 20% above the ideal body weight. In recent years, overweight and obesity have increased markedly and contributing factors include a social environment that supports physical inactivity, excessive food consumption, and unhealthy food choices. Overweight and obesity, is a major risk factor associated with a wide number of health problems including hypertension, hyperlipidemia, diabetes, surgical risks, pulmonary and renal problems, pregnancy complications and certain type of cancer. 3350 J. Med. Plants Res. Increased consumption of sugar leads to several nutritional and medicinal problems such as obesity. Regular consumption of sugar-sweetened snacks and beverages may cause metabolic disorders, such as obesity. Therefore, an efficacious weight management strategy is to substitute sugar with low calorie sweeteners (Stephen et al., 2010). Stevia leaves contain zero-calorie ent-kaurene diterpene glycosides (stevioside and rebaudiosides) that are not metabolized to produce energy and taste 300 times sweeter than sucrose (Soejarto et al., 1982; Megeji et al., 2005; Walter and Soliah, 2010). In human studies, the measured sweetness of 1 g of crude extract of Stevia leaf dissolved in water ranged from 100 to 150 times that of equivalent concentrations of sucrose (Cardello et al., 1999). Stevia sweeteners in foods and beverages offer low calorie alternative substitute of sugar, assist with weight control and weight loss by restricting or controlling calorie intake in the diet. Ingestion of steviol in high doses showed a reduction in body weight as experimented in rats (Curry and Roberts, 2008). Leaves of S. rebaudiana can also be used as a functional food ingredient and prove beneficial to dietetic practice. In fact, ―replacing intake of added sugars with non-nutritive sweeteners could result in a deficit of 380 cal/day or 1 pound of weight loss in 9 to 10 days, if intake was at 95 g (24 tsp) daily‖ (8 Position of JADA). Stevia can be used in place of sugar as they provide fewer calories per gram than sugar which is not completely absorbed by digestive system. Consumption of Stevia leaves and extract reduce the carving for sweet and fatty foods and are useful in weight loss programme (Jain et al., 2007). Inflammatory bowel disease (IBD) IBD is a group of inflammatory conditions of the colon and small intestine. The two major forms are Crohn’s disease and ulcerative colitis. The onset of IBD occurs most often in patients between the ages of 15 and 30 years, and both sexes are equally affected. In each case, the cause is unknown but genetic predisposition and immune and autoimmune phenomena are involved (Kornbluth et al., 1998). Stevia and its polyphenolic compounds steviol and stevioside exert anti-inflammatory effects on colonic epithelial cells. Shiozaki et al. (2006) conducted the study on animals and observed that stevioside inhibit intestinal smooth muscle contraction, stimulation of which is linked to hypermotility-associated diarrhea. Pariwat et al. (2008) studied the stevioside and its similar compounds steviol, dihydroisosteviol, isosteviol and isosteviol 16-oxime, on cAMP-regulated chloride (Cl) secretion in human T84 colonic epithelial cells line and in vivo for their antidiarrheal efficacy, results showed that steviol and its analogs, inhibited cAMP activated Cl secretion in intact T84 cells in a dose-dependent manner. The stevioside ineffectiveness could be due to its molecular bulkiness, rendering it relatively impermeable to cell membranes, and thereby exhibiting a promising agent in antidiarrheal treatment. Similar compounds of dihydroisosteviol could be a new class of cystic fibrosis transmembrane conductance regulator inhibitors that may be useful for further development as antidiarrheal agents. Dental caries Dental caries, also known as tooth decay, is the most prevalent chronic diseases of people worldwide and individuals are susceptible to this disease throughout their lifetime. It is an oral infectious disease in which organic acid metabolites produced by the metabolism of oral microorganisms lead to gradual demineralization of tooth enamel, followed by rapid proteolytic destruction of the tooth structure. Bacteria are an essential part of the tooth decay process. Several microorganisms are capable of fermenting dietary carbohydrate. Streptococcus mutans is the most prevalent followed by Lactobacillus casein and Streptococcus sanguis. Regular consumption of nutritive sweeteners also known as caloric sweeteners or sugars provide energy in the form of carbohydrate, causes cavities which encourage the growth of harmful bacteria in the mouth contributing to plaque formation and gingivitis. There is a requirement to substitute sucrose with natural sweetener which should be nutritionally appropriate and not being detrimental to the overall general health of the individual (Matsukubo and Takazoe, 2010). Stevia, as a non nutritive sweetener are zero- or low-calorie alternatives to nutritive sweeteners, such as table sugar possess bacteriostatic and bacteriocidal properties benefit oral health by eliminating the cause of dental decay and gingivitis. Stevia is a natural sucrose substitute with high nutritional value beneficial in the battle against dental caries. Extract of Stevia leaves and its major secondary metabolites, steviol, isosteviol, stevioside and rebaudioside A, B, C and E are noncariogenic and have been found to inhibit glucan induced aggregation of cariogenic organism, Thus Stevia have potential of providing oral health benefits (Wu et al., 1998). Studies suggested that development of dental caries in rat pups are triggered in presence of sucrose solution while it is not with stevioside (Das et al., 1992). The major cariogenic organism, S. mutans, experiences growth suppression and secretes less acid when grown on media containing stevioside than when grown on sucrose, glucose or fructose media (Grenby, 1991). MARKETING AND USE The excessive sugar intakes have become a major health concern all over the world. This means that majority of our society is at risk for a high number of precarious Gupta et al. health conditions that can lead to various chronic diseases (Anton et al., 2010). The major culprit along with solid fats is a surplus of sugar, which on average provides 35%, or nearly 800 calories/person/day. These disproportionate amounts create elevated levels of at risk members in our society. There is a fundamental need for an alternative sweetener in place of sugar, or other chemical sweeteners. It may have taken a long time for many countries to decide, but today, throughout the world including India, Stevia is growing successfully. It has certainly earned the right to be considered a safe, natural sugar substitute and alternative sweetener used as a functional food ingredient to sweeten a diverse variety of consumer products such as soft drinks, tea, coffee, icecreams, confectionery and bakery, etc. As of 2011, natural sweeteners made from extract of the Stevia plant have taken about 10% of the US consumer market for table-top sugar substitutes, only nine months after being approved by the US Food and Drug Administration. GLG Life Tech, an international Stevia supplier has taken the initiative to introduce Stevia in Indian market and facilitated its production and extraction. Stevia costs 30% less than current sugar prices and its growing popularity has drawn Coca-Cola Company to introduce, develop and commercialize Stevia in its leading brands. Relative to sucrose, the potent sweetness intensities of these glycosides have projected them as cost effective sucrose substitute which demonstrates how a slight alteration in a person’s diet can drastically change their health risk. CONCLUSION The sweet herb S. rebaudiana (Bertoni) has a valuable future and is extensively used in various areas of the world. Stevia and its metabolites have commercial value in number of countries as sugar substitutes in foods, beverages and medicines. Studies have reported the health promoting of this magical natural herb Stevia which is well known as therapeutic agent and an efficient medication for curing chronic diseases. 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