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Only 6 out of 32 studies were assessed as having a low risk of bias due to their strong methodological study designs. In this systematic review, many studies were underpowered, making it difficult to obtain statistically significant, between-group differences. This means that testosterone may have a greater physiological effect in the body when concentrations of these biomarkers are elevated.
The dosages used in the included studies varied widely, making an evaluation of safety and efficacy difficult. Moreover, several studies did not provide specific details of extracts as recommended by the National Center for Complementary and Integrative Health (88), making duplication of those studies difficult. Also, the studies on fenugreek used 4 different extracts, with dosages ranging from 250 mg/d up to 600 mg/d. For example, the studies on ashwagandha used dosages ranging from 240 to 675 mg/d, with varying standardization and extraction processes and different sample types.
Molecular effects of Moringa leaf extract on insulin resistance and reproductive function in hyperinsulinemic male rats. Melatonin controlled apoptosis and protected the testes and sperm quality against bisphenol a-induced oxidative toxicity. Synergistic effect of the hydroalcoholic extract from Lepidium meyenii (Brassicaceae) and Fagara tessmannii (Rutaceae) on male sexual organs and hormone level in rats. Lutein dietary supplementation attenuates streptozotocin-induced testicular damage and oxidative stress in diabetic rats. Hazelnut consumption improves testicular antioxidant function and semen quality in young and old male rats.
A total of 301 participants were recruited for the studies involving Tribulus terrestris, with ages ranging from 18 to 65 y and sample sizes ranging from 21 to 180 participants. Two studies used patented extracts, Trib Gold, manufactured by Nerhadou International, standardized to contain up to 45% steroidal saponins (extract source not provided) (39), and Tribestan, manufactured by Sopharma, delivering a minimum of 675 mg furostanol saponins (from overground parts of the herb) (48). There was no statistically-significant difference in SHBG concentrations between the 2 groups (58). Three studies used the Testofen® extract, manufactured by GencorTM (also known as Fenu-FG) (details of extract preparation not provided) (57, 58, 63) and the other 3 studies used the extracts IND9, manufactured by Indus Biotech® (53), Furosap®, manufactured by Chemical Resources (CHERESO) (42), and an extract standardized for Grecunin, manufactured by Indus Biotech® (64) (details of all extract preparations not provided). The final study using Asian ginseng was conducted in 80 infertile men, aged between 25 and 45 y (56).
In males, there exists an inverse correlation between obesity and testosterone levels (37). However, previous studies have also indicated that smokers tend to have higher testosterone levels compared to non-smokers (35). Long-term alcohol consumption can impair the male gonadal axis and lead to a reduction in testosterone levels (33). However, a study has also shown no association between cholesterol intake and testosterone levels (17).
For example, vitamin D acts as a steroid hormone with a progesterone effect. LH receptors are located on the membrane of Leydig cells, whereas FSH receptors are located on the Sertoli cells. These beneficial changes in semen quality have been reported to improve the chance of natural conception in several but not all studies.
In this study, they found that EGCG (19) inhibited the PKA/PKC signalling pathways and decreased the enzyme activity of Cyp11a1 and Hsd17b3. Therefore, flavanones may have the potential to prevent testosterone decline in response to endocrine disruptors, and possibly to aging. Naringenin (14) also prevented the decreases of serum testosterone and inhibin B in rats receiving chemotherapeutic drugs such as cisplatin and doxorubicin . Naringenin (14, Figure 7), a flavanone found in grapefruits, has been reported to inhibit the activity of Hsd17b3 and Hsd3b in male rats after daily subcutaneous injections of 15 mg/kg . However, others have reported that icariin (11) induces apoptosis in mouse Leydig tumor cells (mLTC1) , suggesting an anticancer potential.
Some researchers opine that the increased intake of certain antioxidants could possibly inhibit this potentially serious issue. For example, given that specific herbs have anti-inflammatory and antioxidant activity, these may provide the greatest benefits for men presenting with excess premorbid inflammation or oxidative stress. Finally, matching treatment based on presentation may also clarify populations in whom herbal supplementation may be most beneficial. In addition to identifying the effects of herbal supplementation during use, it will be useful to determine the duration of effects once supplementation ceases. In addition, many of the studies included in this review have design flaws that adversely affect the strength of conclusions derived from this systematic review.
A total of 126 male participants were recruited for the studies, with ages ranging from 20 to 56 y and sample sizes ranging from 20 to 56 participants. Two studies used gelatinized maca (41, 52) and 1 study used a dried maca extract (66). Three studies were randomized controlled trials (39, 48, 54) and 1 study was a randomized, double-blind, placebo-controlled trial (61).
Gender: Female