Quick Hit Summary

Testosterone: In the eyes of many, this is the quintessential hormone with respect to muscle mass and sex drive. Thus, for those looking to bulk up and/or improve their sex drive, many find themselves turn to “test” boosting nutraceuticals for support. One of the most popular ones on the market today is Tribulus terrestris. However, as with any supplement, one must ask themselves, “Does it actually work?” Currently, animal based studies have produced mixed results. Although some research indicates that it does lead to small, acute spikes in androgen levels (ie – testosterone & DHT), just as many show it to have little to no effect on enhancing production of these hormones. With respect to the purported aphrodisiac properties of Tribulus, slight to moderate improvements in sex drive have been noted in rats post supplementation. With respect to its anabolic effects, one study has shown significant weight gain post supplementation. What about in humans? That question will be answered in part II of our short mini-series exploring the supposed benefits of Tribulus.

Testosterone – Come Get Some!

Figure 1 The chemical structure of testosterone. Image Source²³

Muscle & Sex, Sex & Muscle, Sex and More Sex, Muscle and More Muscle; If person “A” walks into a nuetraceutical store, I’d be willing to bet money that they’re looking to purchase a supplement that either A) enhances muscular development and physical performance or B) Improves their sex life. How can I be so confident in what they will purchase? Well, as you may recall from our interview with the FDA, the top two categories of supplements on the market today are those which purportedly accomplish one of these two tasks.

Let’s say that we were to design a supplement that “killed 2 birds with 1 stone”, improving both physical development as well as sexual prowess. Our efforts would be focused on one thing – ensuring optimal levels of testosterone and its derivative, dihydrotestosterone (DHT); These hormone are essential for muscular growth and sexual function¹². However, although DHT levels appear to stay consistent with age, testosterone peaks between 2nd and 3rd decades of one’s life before starting a slow gradual decline.³⁴ In one study, involving > 1000 middle aged and older men (Mean: 55.2 +/- 8.7 yrs ; Range: 40-70 yrs), it was found that total testosterone decreased by 1.6%/yr and biologically available testosterone decreased by 2-3%/yr⁵. Thus, for competitive athletes looking to improve physical performance, as well as those looking to avoid the age related decline in testosterone levels (and potentially sexual performance), many turn to neutraceuticals for support.

One of the most widely promoted testosterone boosters on the market is Tribulus. This supplement, commonly referred to as “Trib” or “puncture vine”, is derived from Tribulus terrestris, a plant native to southern Europe, Africa, temperate and tropical Asia⁶. Doing a quick search on the internet one finds that the benefits of this plant are of mythical proportions, capable of safely and effectively replacing artificial steroids⁷. Additionally, athletes of all types experience “dramatic performance improvements” via enhanced testosterone production upon taking Tribulus⁸. Furthermore, it appears that Tribulus was the “secret weapon” that fueled the success behind the legendary Bulgarian weightlifting teams⁹. In terms of sexual function, claims have been made the Tribulus “supports reproductive health and boost libido.”¹⁰ And we all know that if something appeared on the internet, it HAS to be fact… right?!?!?

So what is the truth behind Tribulus, will it spike your testosterone levels, causing your strength levels to shoot through the ceiling and give you the sexual prowess of a 20 year old? Or, is it like so many other supplements on the supplement shelves today –> Pure marketing hype? To answer this question, let’s put on our thinking caps and see what science has to say about good ol’ tribulus!

How does Tribulus work?

Taking a peak at the Androgenic Hormones

Although I tried my best not to go too in-depth on the relationship between the androgenic hormones (testosterone, DHT, DHEA, etc), the following section still gets a little technical. If you find yourself confused while reading it, just refer to Figure 2 for reference and skip to the Animal Section of this article or the Human Section in Part II of this series.

Figure 2. The Relationship between Androgenic Hormones. PLEASE NOTE this is a simplified version of the interaction between the various androgenic hormones. Figure created by Sean Casey

Before we go too deep in the research regarding the supposed benefits of tribulus, let’s first review testosterone, its fellow androgens and where/how this “magical” supplement fits into the picture. As seen in Figure 2, there are 2 routes by which testosterone is produced in the body. In males, following puberty, the predominant source of testosterone comes via the Hypothalmic–Pituatory–Gonadol Axis. The amount of testosterone produced by this pathway is controlled by circulating levels of testosterone (as well as direct neural input)¹¹. When testosterone levels are low, this pathway is stimulated, resulting in the release of gonadotrophin releasing hormone (GnRH) which causes the anterior pituitary to release luteinizing hormone (LH). Upon traveling to the testes, LH stimulates the production of testosterone in the leydig cells. In turn, this testosterone can directly act on various tissues in the body or be converted into DHT. Although DHT exerts little direct anabolic effect on skeletal muscle, it is 10x more potent than testosterone with respect to its binding affinity to androgen receptors in other tissue¹². Additionally, testosterone can aromatize (ie- converted) into estrogen.¹³ Contrary to what you may be led to believe estrogen is not a useless hormone in males.

The other pathway, by which testosterone is manufactured in the body is via the Hypothalmic–Pituatory-Adrenal Axis. This route of testosterone production is kick started when corticotropin-releasing hormone (CRH), released from the hypothalamus, enters the anterior pituitary and stimulates the release of adrenocorticotropic hormone (ACTH). Upon synthesis, ACTH travels to the adrenal glands where it facilitates the production the androgens known as dehydroepiandrosterone (DHEA) and androstenedione (Andro)¹³, both of which can be converted into testosterone.

To what degree does each pathway contribute to testosterone and DHT production? That question is somewhat hard to answer. However, males have circulating testosterone levels ~10x greater than females; This can largely be attributed to the presence of the leydig cells of the testes (which is part of the the Hypothalmic–Pituatory–Gonadol Axis).¹¹ That said, according to Vingren et al, the Hypothalmic–Pituatory -Adrenal Axis route of manufacture “… along with peripheral conversion of androgens, is the primary source of testosterone in females and adolescent boys.”¹¹

For an in-depth discussion on the endproducts of these androgenic pathways, (which is beyond the scope of this article), I would like to refer you to the following articles by our friends at SuppVersity:

• Testosterone & Muscle Building Part I
• Testosterone & Muscle Building Part II
• Testosterone & Muscle Building Part III
• Estrogen: Friend or Foe?
• Dihydrotestosterone (DHT) - Bigger, Stronger, Faster or just Balder, Fatter and Unhealthier?

Where does Tribulus Fit Into The Picture?

Okay, now that we have a baseline understanding of the relationship between the various androgenic hormones, let’s take a peak at how Tribulus terrestris MAY enhance testosterone & DHT production …Well, truth be told, this is a rather cloudy topic that lacks a definitive answer. However, it’s been hypothesized that its muscle boosting and aphrodisiac properties are attributed to the presence of a steroidal glycosides compound called protodioscin (PTN).¹⁴ According to Gauthaman & Adaikan,

“The steroidal nature of this compound may facilitate its role as an intermediary in the steroidal pathway of androgen production. It may act either by binding to hormone receptors or to enzymes that metabolize hormones.”¹⁴

However, it’s ability to act “as an intermediary”, similar to DHEA and/or Andro, has been questioned by other research groups. In a study completed by Rogerson et al²¹, which will be discussed in greater deal in Part II of this write-up, it was found that tribulus supplementation of 450 mg in 22 elite male rugby athletes (5 weeks) did not lead to changes in the urinary testosterone/epitestosterone ratio. Similar results were found by Sauden et al. in their small case study which involved giving 2 healthy women 1500 mg for two days.²² Thus, Sauden et al concluded that Tribulus “… may not be considered a direct precursor of testosterone…” For reference, the urinary testosterone/epitestosterone ratio is used by the World Anti-Doping Agency (WADA) to assess exogenous steroid and/or its precursor use in athletes.

A Quick Note: Sex Hormone Binding Globulin (SHBG)

Before we get too deep into the research regarding the effects of Tribulus on the androgenic hormones, I must mention that most of the studies that are discussed in this article examine the effects of Tribulus on total testosterone levels which includes free testosterone as well as that which is bound to a circulating proteins such as Sex Hormone Binding Globulin (SHBG). When bound to SHBG, testosterone is unable to enter into one’s cells, thus limiting the hormones ability to carry out the effects associated with it. Thus, for those looking to “jack up” on the anabolic/aphrodisiac/etc properties of testosterone, the goal is to increase the free form of it. However, there are a couple of reasons as to why total testosterone vs. free testosterone is used in most studies. First, the gold standard techniques to measure free testosterone (AFTC & non-SHBG-T) are time consuming and costly¹⁵. In addition, considerable error can be involved when quicker methods, commonly used in practice, are used estimate free testosterone¹⁵¹⁶¹⁷.

Animal Based Studies: Tribulus and Androgenic Hormones

One of the most widely referenced studies used by manufactures to promote the testosterone “spiking” abilities of Tribulus was completed by Gauthaman & Adaikan. In their study, the research team examined both the acute and chronic effect of taking various tribulus doses on androgenic hormones.¹⁴ In their acute study, the research team gave 5 primates (2 baboons, 3 rhesus monkeys) various doses of Tribulus via injections. For the following 180 minutes, the research team examined the changes in testosterone, DHT & DHEAS (which is the sulfated version of DHEA; Refer to Figure 2.). The human equivalent doses received by each animal were as follows:

Rhesus Monkeys

• Group 1: 5.2 mg/lb (2.4 mg/kg)
• Group 2: 10.6 mg/lb (4.8mg/kg)
• Group 3: 21 mg/lb (9.6 mg/kg)

Baboons

• Group 1: 8.9 mg/lb (4.1mg/kg)
• Group 2: 17.9 mg/lb (8.1 mg/kg)
• Group 3: 35.7 mg/lb (16.2 mg/kg)

At the conclusion of the acute portion of the study, Gauthaman & Adaikan found that vs. baseline values, Tribulus supplementation had no significant affect on DHEAS levels. However it did acutely raise testosterone (~ 50% regardless of group) and DHT levels by (29-47%). These androgen spike were short lived, peaking ~30 minutes after receiving the tribulus injections before returning to baseline.

The chronic phase of Gauthaman & Adaikan’s study involved 24 rabbits and 48 rats. Over the course of 8 weeks, these animals orally ingested Tribulus in the following HED¹⁴:

Rabbits

• Group 1: Control
• Group 2: 1.8 mg/lb/d (0.8 mg/kg/d)
• Group 3: 3.6 mg/lb/d (1.6 mg/kg/d)
• Group 4: 7.2 mg/lb/d (3.2mg/kg/d)

Rats

Groups 1-4 were “intact”/non-castrated; In contrast, the rats in Group 5 were castrated

• Group 1: Control
• Group 2: 0.9 mg/lb/d (0.4 mg/kg/d)
• Group 3: 1.8 mg/lb/d (0.8mg/kg/d)
• Group 4: 3.6 mg/lb/d (1.6 mg/kg/d)
• Group 5 (castrated rats): 1.8 mg/lb/d (0.8mg/kg/d)

Tribulus supplementation did not increase testosterone levels in any of the “intact” groups (Although non statistically significant, increases between 20-38% were noted). However, castrated rats experienced a statistically significant 25% increase in testosterone levels.¹⁴ With respect to DHT levels, significant increases were noted in Group 3 (30%) and Group 4 (32%) of the rabbits as well as group 5 of the rats (15%).

Martino-Andrade et al. also examined the relationship between “chronic” Tribulus supplementation and testosterone production.¹⁸ In their study, intact rats were given various amounts of Tribulus as part of their normal daily diets for 28 straight days. For reference, rats received 3.9 mg/lb(1.76 mg/kg), 14.8 mg/lb (6.72 mg/kg) or 38.8 mg/lb (17.6 mg/kg) per day. At the end of the trial, it was found that regardless of the dose supplemented with, testosterone levels remained unchanged.

Animal Based Studies: Tribulus, Sex Drive & Body Weight Fluctuations

Figure 3 Ok, which one of you spiked the water with Tribulus?!?!? Image Source²⁴

Characteristics of Sexual Behavior as Defined by Gauthamen et al.¹⁹²⁰

• Mount Frequency (MF): the number of mounts without intromission from the time of introduction of the female until ejaculation,
• Intromission Frequency (IF): the number of intromissions from the time of introduction of the female until ejaculation,
• Mount Latency (ML): the time interval between the introduction of the female and the first mount by the male
• Intromission Latency (IL): the interval from the time of introduction of the female to the first intromission by the male (characterized by pelvic thrusting and springing dismount),
• Ejaculation Latency (EL): the time interval between the first intromission and ejaculation (characterized by longer, deeper pelvic thrusting and slow dismount followed by a period
  of inactivity),
• Post-ejaculatory interval (PEI): the time interval between ejaculation and the first intromission of the following series.

The aphrodisiac and anabolic properties of Tribulus have also been examined by various research groups. In a 2002 study, completed by Gauthaman et al, researchers sought to find out if taking a daily HED of 1.8 mg/lb (0.8mg/kg) of Tribulus for 8 weeks would improve sexual behaviors in castrated rats.¹⁹ Referring to the definitions listed above, Guathaman et al found that tribulus supplementation led to “a mild to moderate improvement of the sexual behavior parameters” of castrated rats vs. non supplemented castrated rats. Those taking the supplement experienced increased MF (11.86%) and IF (18.46%) as well as decreased ML (10.57%), IL (20.65%), EL (16.41%). All these improvements were statistically significant. With respect to the anabolic effect of the supplement, there were no significant differences in overall body weight between those which did and did not receive the supplement.

In a follow-up study, the research team carried out an 8 week study examining the effects of various doses tribulus on sexual behavior in non-castrated rats. In this latter study, 40 “intact” rats were randomly divided into the following 4 groups¹⁹:

• Group 1: Control
• Group 2: 0.9 mg/lb/d (0.4 mg/kg/d)
• Group 3: 1.8 mg/lb (0.8mg/kg/d)
• Group 4: 3.6 mg/lb (1.6 mg/kg/d)

Results of the study indicated that Tribulus led to improvements in “sexual behavior” as shown below in Table 1. I must point out that all male rats, regardless of if supplemented or not, did respond to the presence of the females… some just quicker than others! They also found greater gains in weight amongst those taking tribulus. Unfortunately, Gauthaman et al. did not assess whether or not this change in weight was due to gains in lean mass or fat tissue.²⁰ (I know, I know, I also was disappointed that they did not examine the type of weight gain either!)

Characteristic	Group 2	Group 3	Group 4
Weight Gain	+ 9%	+ 23% *	+ 18% *
MF	+ 12%	+ 27% *	+ 24% *
IF	+ 16%	+ 19% *	+ 22% *
ML	- 16% *	- 23% *	- 22% *
IL	- 2%	- 7%	- 6%
EL	- 12%	- 27% *	- 18% *
PEI	- 13%	- 20% *	- 16%

Table 1. The effects of various doses of Tribulus terrestris¬ on sexual performance and weight gain in healthy rats. Please know that the figures below represent significant differences vs. control groups. “+” refers to increase in activity; “-“ refers to significant decrease in activity. “*” indicates significantly different from control group. Data obtained from Gauthaman et al.²⁰

Of interest, increasing the dose of tribulus beyond 1.8 mg/lb (0.8mg/kg), did not lead to greater gains in sexual behavior or body weight. Gauthaman et al. hypothesized that this may have been a result of saturating all of the receptors in the body with tribulus, thus leading to no further increase/decrease in measured behaviors.

Animal Studies – In Summary

In animal studies, weak to moderate evidence exists indicating that Tribulus does stimulate androgenic hormone production (albeit short lived and not observed in all studies¹⁸). In addition, enhanced sexual activity in both “in-tact” and castrated rats as well as increases body weight in intact rats has been noted. However, as beneficial as animal studies are with respect to furthering our knowledge, one cannot freely assume that they will perfectly translate over to humans. (Please refer to Making Sense of Animal Studies for further discussion on this topic.)

Thus, before you rush out to your favorite Nutraceutical/Supplement store and buy them out of their Tribuls supply, I strongly encourage you to relax, sit back and read Part II of my look at Tribulus supplements.

References

¹ Traish AM. Androgens play a pivotal role in maintaining penile tissue architecture and erection: a review. J Androl. 2009 Jul-Aug;30(4):363-9. Epub 2008 Sep 18.

² Bhasin S, Woodhouse L, Casaburi R, Singh AB, Bhasin D, Berman N, Chen X, Yarasheski KE, Magliano L, Dzekov C, Dzekov J, Bross R, Phillips J, Sinha-Hikim I, Shen R, Storer TW. Testosterone dose-response relationships in healthy young men. Am J Physiol Endocrinol Metab. 2001 Dec;281(6):E1172-81.

³ Araujo AB, Wittert GA. Endocrinology of the aging male. Best Pract Res Clin Endocrinol Metab. 2011 Apr;25(2):303-19.

⁴ Swerdloff R, Wang C. Testosterone treatment of older men—why are controversies created? J Clin Endocrinol Metab. 2011 Jan;96(1):62-5.

⁵ Feldman HA, Longcope C, Derby CA, Johannes CB, Araujo AB, Coviello AD, Bremner WJ, McKinlay JB.Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts male aging study. J Clin Endocrinol Metab. 2002 Feb;87(2):589-98.

⁶ Halvorson, WL, Guertin P. Fact Sheet for: Tribulus terrestris L. US Geological Survey/Southwest Biological Science Center. December 31, 2003. Accessed January 8, 2012 from:http://sdrsnet.srnr.arizona.edu/data/sdrs/ww/docs/tribterr.pdf

⁷ Chinese Herbs. Accessed January 8, 2012 from: http://www.chinese-herbs.org/tribulus-terrestris/tribulus-and-bodybuilding.html

⁸ Tribulus terrestris maximum strength raw testosterone enhancer. Accessed January 8, 2012 from: http://www.247bodybuilding.com/tribulus.htm

⁹ Truly Huge Fitness tips. Accessed January 8, 2012 from: http://www.trulyhuge.com/news/tips02.htm

¹⁰ Support Reproductive Function And Boost Libido With Tribulus Terrestris. Accessed on January 8, 2012 from: http://www.thehealthyvillage.com/diet-and-nutrition/supplements/support-reproductive-function-and-boost-libido-with-tribulus-terrestris.html

¹¹ Vingren JL, Kraemer WJ, Ratamess NA, Anderson JM, Volek JS, Maresh CM.
Testosterone physiology in resistance exercise and training: the up-stream regulatory elements. Sports Med. 2010 Dec 1;40(12):1037-53.

¹² Grino PB, Griffin JE & Wilson JD. Testosterone at high concentrations interacts with the human androgen receptor similarly to dihydrotestosterone. Endocrinology 1990 Feb; 126(2): 1165–1172.

¹³ Nakamura Y, Hornsby PJ, Casson P, et al. Type 5 17betahydroxysteroid dehydrogenase (AKRIC3) contributes to testosterone production in the adrenal reticularis. J Clin Endocrinol Metab 2009 Jun; 94 (6): 2192-8

¹⁴ Gauthaman, K., Adaikan, P.G.. The hormonal effects of Tribulus terrestris and its role in the managementof male erectile dysfunction – an evaluation using primates, rabbit and rat. Phytomedicine 15 (2008) 44– 54

¹⁵ A critical evaluation of simple methods for the estimation of free testosterone in serum. Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999 Oct;84(10):3666-72.

¹⁶ Cunningham GR, Toma SM. Clinical review: Why is androgen replacement in males controversial? J Clin Endocrinol Metab. 2011 Jan;96(1):38-52. Epub 2010 Sep 29.

¹⁷ de Ronde W, van der Schouw YT, Pols HA, Gooren LJ, Muller M, Grobbee DE, de Jong FH. Calculation of bioavailable and free testosterone in men: a comparison of 5 published algorithms. Clin Chem. 2006 Sep;52(9):1777-84. Epub 2006 Jun 22.

¹⁸ Martino-Andrade AJ, Morais RN, Spercoski KM, Rossi SC, Vechi MF, Golin M, Lombardi NF, Greca CS, Dalsenter PR. Effects of Tribulus terrestris on endocrine sensitive organs in male and female Wistar rats. J Ethnopharmacol. 2010 Jan 8;127(1):165-70. Epub 2009 Sep 23.

¹⁹ Gauthaman K, Adaikan PG, Prasad RN. Aphrodisiac properties of Tribulus Terrestris extract (Protodioscin) in normal and castrated rats. Life Sci. 2002 Aug 9;71(12):1385-96.

²⁰ Gauthaman K, Ganesan AP, Prasad RN. Sexual effects of puncturevine (Tribulus terrestris) extract (protodioscin): an evaluation using a rat model. J Altern Complement Med. 2003 Apr;9(2):257-65.

²¹ Rogerson S, Riches CJ, Jennings C, Weatherby RP, Meir RA, Marshall-Gradisnik SM.The effect of five weeks of Tribulus terrestris supplementation on muscle strength and body composition during preseason training in elite rugby league players. J Strength Cond Res. 2007 May;21(2):348-53.

²² Saudan C, Baume N, Emery C, Strahm E, Saugy M. Short term impact of Tribulus terrestris intake on doping control analysis of endogenous steroids. Forensic Sci Int. 2008 Jun 10;178(1):e7-10. Epub 2008 Feb 20.

²³ Klaus Hoffmeier. Chemical Structure of Testosterone. This file is ineligible for copyright and therefore in the public domain, because it consists entirely of information that is common property and contains no original authorship. Accessed January 18th 2012 from:http://commons.wikimedia.org/wiki/File:Testosterone.PNG

²⁴ Rats Socialism. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.Accessed January 18th 2012 from:http://commons.wikimedia.org/wiki/File:Rats_socialising.jpg