Williamson G, Coppens P, Serra-Majem L, Dew T. Review of the efficacy of green tea, isoflavones and aloe vera supplements based on randomised controlled trials. Food Funct. December 2011;2(12):753-759.

Various botanicals and their preparations and derivatives are used in products promoted for their beneficial health effects. These European authors conducted a review of the literature to assess the evidence for health benefits of three commonly used plant food supplements (PFS): green tea (Camellia sinensis) (12 studies or reviews cited), isoflavones (23 studies or reviews cited), and aloe (Aloe vera) (9 studies or reviews cited).

The authors explain that because the criteria applied by the European Food Safety Authority to evaluate the health effects of food components relies on the well-defined characterization of the food component and measurable biomarkers, it can only be applied to well-defined extracts or pure compounds isolated from plant material. Its application to botanicals and botanical preparations is limited because the compounds responsible for specific effects are not identified and the effects may be diffused and not linked to specific markers. For the continued use of botanicals, traditional use has been suggested as a valid and essential element of the totality of evidence to substantiate health effects. The authors discuss proposed criteria relating to the various sources of documentation for traditional use.¹

The authors' review includes many studies indicating that green tea has positive effects in various health areas, including metabolic syndrome, cognitive function and neuroprotection, cancer, bone health, and arthritis. Unfortunately, say the authors, there are few health areas where sufficient randomized, controlled trials (RCTs) have been conducted to properly judge the efficacy of oral green tea intervention. In a meta-analysis of 133 RCTs on flavonoid-rich foods and cardiovascular disease risk factors, green tea consumption significantly reduced low-density lipoprotein cholesterol.² Other systematic reviews and meta-analyses consider green, black, and oolong teas together, consumed as both infusions and extracts. "It is only in the area of the metabolic syndrome that the number of RCTs indicated is approaching sufficient to judge such efficacy," write the authors. For example, in a meta-analysis of 11 green tea intervention studies with 1,226 participants, green tea catechins plus caffeine were effective in promoting weight loss and maintaining weight after a period of negative energy balance.³ The importance of caffeine was also highlighted in a meta-analysis⁴ of 15 trials with 1,243 participants, in which green tea catechins taken alone had no significant effect on the endpoints (body weight, waist circumference, waist-to-hip ratio, and body mass index), but green tea catechins combined with caffeine significantly decreased body weight compared with a noncaffeinated control. In that same analysis, body weight, waist circumference, and body mass index were all decreased by green tea catechins plus caffeine intervention compared with a caffeine control.

RCTs indicate that isoflavones can affect bone resorption at lower doses in postmenopausal women with estrogen-related bone loss, but "this is only translated to attenuation of bone loss at higher doses of isoflavones," say the authors. They cite a review⁵ of 28 studies involving 2,477 subjects in RCTs and a meta-analysis⁶ of nine RCTs using 432 subjects.

The effects of isoflavones on bone mineral density are less clear. A cited systematic review of 12 studies involving 1,433 subjects⁷ and a meta-analysis of 10 studies using 608 subjects⁸ offered conflicting results. The authors' review of RCTs (which included five systematic reviews of 99 studies) concluded that the effects of isoflavones on hot flashes in postmenopausal women were variable and that no firm conclusions could be made.

"Despite the popularity of aloe as a PFS, the evaluation of its efficacy as a coadjuvant therapy for certain metabolic or digestive pathologies remains scarce," state the authors. It is a typical example of a naturally occurring ingredient whose efficacy in topical applications presupposes its efficacy in oral applications. Nonrandomized, clinical trials and case reports suggest the use of aloe in improving fasting blood glucose levels. In a cited review⁹ of eight trials with 5,285 subjects, the evidence suggests a trend toward the benefit of oral aloe use in reducing fasting blood glucose concentration. Although there are some promising results with the use of aloe for diverse dermatological conditions, say the authors, its clinical effectiveness has not been sufficiently studied. A certain degree of efficacy was demonstrated for aloe gel in the treatment of oral lichen planus in a well-designed RCT,^10,11 and a systematic review supported the use of aloe as an effective intervention in burn wound healing for first- to second-degree burns.¹² The authors note that aloe ingestion has been associated with diarrhea, electrolyte imbalance, kidney dysfunction, and interactions with conventional drugs, and that its topical use has been associated with episodes of contact dermatitis, erythema, and phototoxicity.

The authors conclude that, in general, conclusive results on PFS should be established in the future by conducting studies with more homogeneous populations, by using supplements with optimized and measured bioavailibility, and by conducting larger RCTs using validated biomarkers for as long as needed to make conclusive results on a putative effect.

―Shari Henson

References

¹Anton R, Serafini M, Delmulle L. Food Sci Technol Bull. 2011. In press. [Note: The authors of the original article did not provide the title name for this citation. A search of the Internet also provided no results.]

²Hooper L, Kroon PA, Rimm EB, et al. Flavonoids, flavonoid-rich foods, and cardiovascular risk: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2008;88(1):38-50.

³Hursel R, Viechtbauer W, Westerterp-Plantenga MS. The effects of green tea on weight loss and weight maintenance: a meta-analysis. Int J Obes (Lond). 2009 Sep;33(9):956-961.

⁴Phung OJ, Baker WL, Matthews LJ, Lanosa M, Thorne A, Coleman CI. Effect of green tea catechins with or without caffeine on anthropometric measures: a systematic review and meta-analysis. Am J Clin Nutr. 2010;91(1):73-81.

⁵Taku K, Melby MK, Kurzer MS, Mizuno S, Watanabe S, Ishimi Y. Effects of soy isoflavone supplements on bone turnover markers in menopausal women: systematic review and meta-analysis of randomized controlled trials. Bone. 2010;47(2):413-423.

⁶Ma DF, Qin LQ, Wang PY, Katoh R. Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials. Eur J Clin Nutr. 2008;62(2):155-161.

⁷Ricci E, Cipriani S, Chiaffarino F, Malvezzi M, Parazzini F. Soy isoflavones and bone mineral density in perimenopausal and postmenopausal Western women: a systematic review and meta-analysis of randomized controlled trials. J Womens Health (Larchmt). 2010;19(9):1609-1617.

⁸Ma DF, Qin LQ, Wang PY, Katoh R.  Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta-analysis of randomized controlled trials. Clin Nutr. 2008;27(1):57-64.

⁹Ngo MQ, Nguyen NN, Shah SA. Oral aloe vera for treatment of diabetes mellitus and dyslipidemia. Am J Health Syst Pharm. 2010;67(21):1804-1811.

¹⁰Feily A, Namazi MR. Aloe vera in dermatology: a brief review. G Ital Dermatol Venereol. 2009;144(1):85-91.

¹¹Choonhakarn C, Busaracome P, Sripanidkulchai B, Sarakarn P. The efficacy of aloe vera gel in the treatment of oral lichen planus: a randomized controlled trial. Br J Dermatol. 2008;158(3):573-577.