Whether licorice consumption affects testosterone levels is still unknown, as conflicting results have been obtained from clinical studies. Armanini et al have conducted a series of trials investigating the effects of licorice on testosterone levels in males with mixed results.
One study showed that licorice (7 g/day equivalent to 0.5 g GA) was able to reversibly reduce testosterone levels within 7 days, by inhibiting 17,20-lyase (involved in the conversion of 17-hydroxyprogesterone to androstenedione) and 17-beta-hydroxysteroid dehydrogenase (involved in the conversion of androstenedione to testosterone). Another study twice attempted to replicate these results, but was unable to detect an effect on testosterone levels in either study; the authors suggest that inappropriate use of statistical tests in the first study may explain the varying results.
More clinically promising are the results from a small trial of nine healthy women (22-26 years) in the luteal phase of their menstrual cycle. The women received 3.5 g licorice (containing 7.6% w/w of GL) daily for two cycles. Total serum testosterone decreased from 27.8 (±8.2) to 19.0 (±9.4) ng/dL in the first month and to 17(±6.4) ng/dL in the second month of therapy (Armanini et al 2004). Further larger scale trials are required to confirm these effects in women with conditions of elevated testosterone such as hirsutism and PCOS.
Licorice contains isoflavones, including licochalcone-A, which are also known as ‘phyto-oestrogens’ because they act as partial oestrogen agonists in the body. Additionally, in vitro studies suggest that stimulation of aromatase activity promotes oestradiol synthesis.
Liquiritigenin and isoliquiritigenin have displayed oestrogenic affinity to sex hormone-binding globulin and oestrogen receptors in vitro and glabridin and glabrene have both demonstrated oestrogen-like activities similar to oestradiol-17(beta) in animal studies.
In vitro studies also suggest the potential for glabridin to enhance osteoblast function. As a result glabridin has been proposed as a possible therapeutic aid in the prevention of osteoporosis and inflammatory bone diseases, as well as cardiovascular diseases and bone disorders, in postmenopausal women.
Although immunostimulating effects have been observed in experimental models, elevated cortisol levels, which are also induced by licorice, may theoretically reduce this effect.
INHIBITION OFALDOLASE REDUCTASE
In vitro studies show that licorice may suppress sorbitol accumulation in red blood cells by inhibiting aldolase reductase. The isoliquiritigenin component appears to be responsible. This may have positive implications in diabetes.
ANTIDEPRESSANT (SEROTONIN REUPTAKE INHIBITION)
Several flavonoid constituents in licorice (glabridin 60%, 4’-O-methylglabridin 53% and glabrene 47%) inhibit serotonin reuptake in a dose-dependent manner, according to in vitro research. An antidepressant activity could theoretically result, although this remains to be tested clinically.