Testosterone Boosters Intake in Athletes: Current Evidence and Further Directions

1. Introduction

At the moment, there is a wide variety of supplements that, according to manufacturers, “increase serum testosterone level”—these supplements are called “testosterone boosters” (TB). Typically, TB contain a combination of a variety of natural substances but do not contain testosterone or other anabolic agents. The consumption of TB may be popular among athletes due to understanding the importance of testosterone in various aspects of sports performance, especially strength [1,2], and with the ever-improving detection of anabolic agents, which are on the WADA Prohibited List [3]. Another reason for the popularity of TB is the increasing recognition of RED-S (Relative energy deficiency in sport) syndrome, which includes low testosterone levels in athletes, and the constant seeking for legal strategies for increasing testosterone among such athletes [4]. At the same time, there is insufficient evidence, both about the safety and the real effectiveness of TB as agents of increasing testosterone levels in the body. In this regard, the study of data on the effectiveness of various components of TB is of great interest.

Most research on TB focuses on the treatment of erectile dysfunction [5], decreased libido [6], late-onset hypogonadism [7], and benign prostatic hyperplasia [8]. Several components of TB may be effective in the treatment of these diseases. In addition, there is a growing interest in the effects of TB on muscle strength and power. One of the first such studies was performed in Bulgaria, where Tribulus terrestris was promoted among weightlifters [9,10]. Other substances are also being actively researched. For example, Chen et al. showed that the combination of Eurycoma longifolia and resistance training improved peak power output in young males [11]. The relationship between boron intake and lean body-mass changes was discussed in another study [12]. Ashwagandha may help to increase muscle mass [13] as well as velocity, power, and maximal oxygen uptake (VO₂ max) in healthy young men [14]. It is assumed that if TB increases testosterone levels, then they may also improve strength, power, and other parameters related to testosterone [10,11].

However, at the same time, there is very little evidence that a particular substance contained in TB actually increases serum testosterone concentration. In one of the largest studies on this topic, Clemesha et al. analyzed the available evidence base of the effectiveness of 109 substances contained in the 50 most popular TB, which were given by the Google search engine [15]. In 90% (n = 45) of the cases, the manufacturer claimed that their TB “increases testosterone levels” or “increases free testosterone levels”. In 62% of cases (n = 31), the manufacturer stated that the supplement “helps to build muscle mass”, and in 50% (n = 25) that the supplement “increases libido”. On average, one TB contained 8.3 individual substances. The most commonly found substances were zinc, fenugreek, vitamin B6, Tribulus terrestris, magnesium, boron, diindolmethane, Eurycoma longifolia, and maca. Clemesha et al. found that 67 out of 109 individual substances had no studies on their effects. For 19 substances (17.4%), there was only 1 study that examined their effect on testosterone levels; for 13 supplements (11.9%) there were 2 studies; for 3 supplements (2.8%) 3 studies; for 4 supplements (3.7%) 4 studies, for 1 supplement (0.9%) 5 studies; and for 1 supplement (0.9%) 6 studies were conducted. According to Clemesha et al., only in relation to 12 substances, all confirmed an increase in the concentration of testosterone: Anacyclus pyrethrum; Bulbine natalensis; Eurycoma longifolia (Tongkat Ali); fenugreek; horny goat weed; L-arginine; L-carnitine; magnesium; Mucuna pruriens; pantothenic acid; selenium; and shilajit [15].

Another review by Balasubramanian et al. analyzed the 5 most popular TB sold on Amazon.com and identified the 10 most common substances in them: Eurycoma longifolia (Tongkat Ali); horny goat weed; maca; nettle; ashwagandha root; Serenoa repens; boron; fenugreek; bioperine; and diindolylmethane [16]. According to these authors, only 5 out of 10 substances have scientific evidence that they can increase testosterone levels: Eurycoma longifolia (Tongkat Ali), Serenoa repens, boron, ashwagandha root, and fenugreek [16].

Our study aimed to evaluate the available evidence on the efficacy of individual TB components on healthy adults or athletes in order to establish the existing evidence base behind their use. The main hypothesis was that, for the vast majority of TB components, there is currently no high-quality evidence of efficacy in increasing testosterone levels in a group of healthy adults or athletes.

2. Materials and Methods

We used the following methodology for our narrative review: (1) the configuration of a working group: two operators skilled in sports supplementation; (2) formulation of the revision question based on considerations made in the abstract: “for the vast majority of TB components, there is currently no high-quality evidence of efficacy in increasing testosterone levels in a group of healthy adults or athletes”; (3) identification of relevant studies on PUBMED and Cochrane Library; and, (4) analysis and presentation of the outcomes: the data extrapolated from the revised studies were carried out in the form of a narrative review.

The keywords for our search included 12 substances that previously showed increased testosterone levels [15]. These are Anacyclus pyrethrum; Bulbine natalensis; Eurycoma longifolia (Tongkat Ali); fenugreek; horny goat weed; L-arginine; L-carnitine; magnesium; Mucuna pruriens; pantothenic acid; selenium; and shilajit [15]. In addition, three substances commonly found in TB from a study by Balasubramanian et al. [16], which had evidence that they may increase testosterone levels—saw palmetto, boron, and ashwagandha root—were analyzed separately. We used the names of the substances that produced the most results, grouped in inverted commas (“…”). The Boolean operator AND that allows the establishment of logical relations among concepts was used. Thus, a typical search was: “Testosterone” AND “substance name” (e.g., “fenugreek”).

The relevant studies were identified using advancing search modality; no time limits were applied. Only studies in English were searched. The selected studies were checked out based on title and abstract (AL, EB) to exclude irrelevant records. The remaining abstracts and subsequent remaining full-text articles were independently screened by 2 authors (AL and EB) for eligibility.

The inclusion criteria for eligible studies were as follows: (1) recruited an adult (age 18–54), healthy male, human population; (2) examined the effects of a single TB component; (3) published in English; and, (4) had pre- and post-testing of testosterone concentrations in male participants. The exclusion criteria were: (1) mean age equal or more than 55 years; (2) combination with other substances used; (3) participation of patients with any disease, including late-onset hypogonadism, obesity, and infertility, etc.; and (4) the studies did not report the required data for analyzing.

The data extrapolated from the revised studies were carried out in the form of a narrative review. The flow diagram of this narrative review has been reported in Figure 1. In our article, we first examined each of the TB components separately and then summarized our review in the discussion.

3. Results

The initial search identified 970 studies, of which 24 studies’ trials were identified as eligible following assessment using the selection criteria (Figure 1).

As a result of the search—only for 10 out of 15 substances (L-arginine; L-carnitine; magnesium; selenium; shilajit; Tongkat Ali; Serenoa repens; boron; ashwagandha root; and fenugreek—24 studies were found that met the inclusion criteria. No such studies were found for five analyzed substances (Anacyclus pyrethrum, Bulbine natalensis, Epimedium (horny goat weed), Pantothenic acid, and Mucuna pruriens).

4. Discussion

In our review, we analyzed studies on the effect of individual TB components on testosterone levels. With regard to 15 analyzed substances, we were able to find only 24 studies evaluating the effect of their isolated course intake on testosterone serum concentration in athletes and healthy adults under 55 years of age. Such studies were carried out in relation to 10 out of 15 substances: L-arginine (3 studies); L-carnitine (2); magnesium (1); selenium (2); shilajit (1); Tongkat Ali (2); Serenoa repens (1); boron (3); ashwagandha root (2); and fenugreek (7). For Anacyclus pyrethrum, Bulbine natalensis, Mucuna pruriens, Epimedium (horny goat weed), and Pantothenic acid, no studies meeting the inclusion criteria were found. Tongkat Ali, ashwagandha, and fenugreek were the substances with the strongest evidence. The positive effect of magnesium and shilajit on testosterone concentration was shown in single studies. Conflicting data were found for L-arginine, L-carnitine, and Serenoa repens. Selenium and boron do not appear to increase testosterone levels.

However, during the search, we found studies that examined the effect of several analyzed substances on serum testosterone concentration among patients with various diseases. For example, several studies have shown the effectiveness of isolated intake of Mucuna pruriens, Serenoa repens, and Eurycoma longifolia on serum testosterone concentration in people with infertility [49], benign prostatic hyperplasia [8], and hypogonadism [7], respectively. There are also studies in which substances were used in combination with other substances [22,23,50]. However, the combined use does not allow assessing the effect of each of the components, and therefore one cannot assert the effectiveness of a particular substance on any parameter.

Smith et al., in their systematic review of the effects of 13 herbs on testosterone concentration, concluded that fenugreek and ashwagandha have positive effects on testosterone concentrations in men [40]. We also found that these substances are most likely to increase testosterone. Also, according to the authors, Tongkat Ali was not classified as a substance with positive effects on testosterone concentration based on one study, while in our work we identified additional studies indicating that Tongkat Ali appears to increase testosterone levels. The main difference from our study was in the analyzed TB components (Smith et al. did not analyze magnesium; selenium; boron; L-arginine; Anacyclus pyrethrum; Bulbine natalensis; Mucuna pruriens; Epimedium; Pantothenic acid; L-carnitine; or Serenoa repens, but did analyze Panax ginseng; Tribulus terrestris; maca; rhodiola; musali; garcinia; forskohlii; reishi; stinging nettle; and Cordyceps sinensis) [40].

Clemesha et al. found 12 substances with nonconflicting data regarding the increase in testosterone levels [15]. The main difference of this work was that the authors looked for studies in men without specific inclusion criteria, while we tried to find studies in healthy men of a specific age group. Among these 12 substances, according to our work, only Tongkat Ali, Ashwagandha, and fenugreek can be classified as substances with the strongest evidence [15].

An interesting novel approach was used by Balasubramanian et al. These authors analyzed the most popular TB on the Amazon website [16]. It is important to note that substances such as Tongkat Ali, ashwagandha, and fenugreek were among the 10 most common components of popular TB, but other components of the most popular TB raise questions about effectiveness. According to the authors, 5 out of 10 of these ingredients (nettle, maca, horny goat weed, Bioperine, and diindolylmethane) had no evidence of any positive effects on testosterone levels at all [16].

It is important to understand the possible mechanisms for increasing testosterone in substances such as Tongkat Ali, ashwagandha, and fenugreek. There are several potential mechanisms for how Tongkat Ali may increase testosterone. First, Eurycoma longifolia contains some biologically active substances (eurycomanones and eurycomanols) that may inhibit the conversion of testosterone to estradiol by the aromatase enzyme, thereby increasing testosterone levels. Second, these substances can increase the release rate of “free” testosterone from the sex-hormone-binding-globulin (SHBG) [34,51]. Possible mechanisms for increasing testosterone by ashwagandha intake are well described in the work of Lopresti et al. [52]. Some studies have shown that ashwagandha can stimulate the release of gonadotropin-releasing hormone (GnRH) and thereby stimulate the secretion of testosterone from Leydig cells [53]. On the other hand, since ashwagandha has antioxidant and anti-inflammatory activity [54], testosterone levels may increase due to a decrease in oxidative stress [52]. A third hypothesis is that ashwagandha can inhibit aromatase, the enzyme that converts testosterone to estradiol [52]. Fenugreek contains a variety of sapogenins such as diosgenin and yamogenin. In particular, diosgenin may be an important precursor in testosterone synthesis [48]. On the other hand, it is suggested that fenugreek can increase testosterone through an aromatase and 5α reductase inhibition [45].

Thus, despite the fact that at the moment there is no unambiguous idea of how Tongkat Ali, ashwagandha, and fenugreek realize their effects, the general mechanisms should be noted as potentially: inhibition of the conversion of testosterone to estradiol by aromatase (all three substances); free testosterone release from the SHBG (Eurycoma); stimulation of the GnRH release (ashwagandha); reduction in overall oxidative stress (ashwagandha); and also being precursors in steroidogenesis (fenugreek).

It is noteworthy that there is still only sporadic evidence of possible side effects associated with the intake of the analyzed substances. For example, there are case reports describing various complications of TB intake [42,55,56,57]. Nguyen et al. described a case of pulmonary embolism in a previously healthy 51-year-old man secondary to fenugreek-containing TB [42]. The patient started taking TB 3 months before he was admitted to the hospital and stopped taking these supplements 1 week before the admission. Interestingly, his total testosterone levels were low [42]. In another case report, Bui et al. reported bilateral pulmonary embolism in a 65-year-old man taking diindolylmethane for 3 months [57]. However, this patient had other thromboembolism risk factors, such as a suspected prior PE, history of tobacco use, age, and obesity [57]. In addition, TB have been linked to pancreatic and hepatic diseases [55,56]. Thus, Almaiman et al. reported a case of abdominal pain and elevation in liver transaminases (AST, ALT) in a 30-year-old athlete taking multicomponent TB [55]. In another case report, authors described acute pancreatitis in a 65-year-old man taking 160 mg of saw palmetto extract for 1 week [56]. The patient had a history of diabetes, hypertension, hyperlipidemia, gout, Barrett esophagitis, and chronic gastritis; however, the further workup excluded cholelithiasis and hypertriglyceridemia as possible causes. The patient denied recent alcohol intake. Despite the fact that the most likely cause of pancreatitis in this case was saw palmetto, the underlying mechanism is unknown [56].

The fact that certain substances reviewed can increase various aspects of physical performance and increase testosterone levels could potentially lead to the inclusion of these substances in the WADA Monitoring program. [57,58]. For example, the steroidlike substance ecdysterone [59], which is present in some TB, is already on the Monitoring list, and some authors demand to prohibit ecdysterone on the basis of single studies conducted on animals and healthy volunteers [60,61].

The limitations of our review include the exclusion of non-English studies, the heterogeneity of individual TB components and their preparations used, and the use of only PubMed and Cochrane Library databases. It should also be noted that almost in all studies meeting the inclusion criteria, serum testosterone analysis was performed using various modifications of the immunoassay method, while more accurate techniques such as mass spectrometry (MS) and liquid chromatography–tandem mass spectrometry (LC–MS) are now available [61].

Our results clearly indicate the need for further high-quality studies assessing the effect of isolated intake of substances contained in TB on serum testosterone concentration in groups of healthy adults. Of particular interest are studies carried out among athletes, even at an amateur level, since potentially TB can fall under the WADA Monitoring program and Prohibited List criteria. It would be very interesting to assess the prevalence of TB consumption among athletes of all levels. Also, it is crucial to examine the safety profile of at least the most popular individual components of TB.

5. Conclusions

Currently, there are only a few studies on the effect of the most popular components of TB on serum testosterone concentration. Most of these studies are of high quality (RCTs), but most often are not performed on athletes.

There is almost no data on the safety profile of various TB components. However, several components may cause coagulation, and hepatic and pancreatic problems; as such, caution is warranted with their use.

Since most TB contain several substances, a substance with unproven efficacy and safety may probably be ingested during TB course intake.

There is a need for further high-quality studies (e.g., RCTs with a structured approach using LC–MS/MS hormonal measurements) assessing the effect of isolated intake of substances contained in TB on serum testosterone concentration in groups of healthy adults.

Based on the review, the authors conclude that at present TB cannot be recommended for use by athletes due to insufficient data on their efficacy and safety.

Author Contributions

Conceptualization, A.L. and E.B.; methodology, A.L. and E.B.; software, A.L.; validation, A.L. and E.B.; formal analysis, A.L. and E.B.; investigation, A.L.; resources, A.L. and E.B.; data curation, A.L.; writing—original draft preparation, A.L.; writing—review and editing, E.B.; visualization, A.L.; supervision, E.B.; project administration, A.L.; funding acquisition, A.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author A.L. upon reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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