Sports Science

Fad or Fact? A Look at Tribulus terrestris

By Edmund R. Burke, Ph.D.

Before the September 1996 issue of Muscle and Fitness came out, few Americans knew of puncture vine, more commonly known by its Latin name, Tribulus terrestris. Used by Eastern European world-champion and Olympic strength and power athletes since the mid-'90s, the herb is purported to build muscle by increasing testosterone production. Even today, only a small group of scientists, herbalists and doctors trained in Oriental and Ayurvedic medicine are knowledgeable about the plant, and little research has been done on it. The research that has been conducted is sketchy. Nonetheless, tribulus is becoming increasingly popular among athletes.

Arguments for the herb's effectiveness are based largely on a few inadequate studies and traditional use. Ancient Greeks used it as a diuretic, a mild laxative and a general tonic. Ayurvedic physicians have long valued the plant for its diuretic properties as well as its aphrodisiac qualities and include it in rejuvenative formulations for treating sexual problems. In China, the herb is frequently used to treat a variety of diseases affecting the liver, kidneys, urinary tract (including urolithiasis, or urinary stones) and cardiovascular system.

Cross-culturally, tribulus is most often used to treat infertility, impotence and libido problems. The herb contains the steroidal saponins terrestrosin, dioscin, gracillin, kikuba saponin, protodioscin, neohecogenin glucoside and tribulosi. According to one paper, the saponins may be responsible for the herb's aphrodisiac properties.¹

Some companies claim that tribulus can decrease fatigue, based on the results of an Indian clinical trial. Researchers investigating tribulus' tonic effects gave a preparation of the herb to 50 men and women who were fatigued and lacked interest in daily activities. Symptoms improved by 45 percent among subjects after taking the herb.²

But it was the search for safe, non-hormonal treatments for infertility and other reproductive disorders that inspired scientists at the Chemical Pharmaceutical Research Institute in Sofia, Bulgaria, to investigate tribulus in the mid-'70s. Based on the study results, Eastern European drug companies began releasing standardized tribulus preparations to treat sexual disorders as early as 1981.

The Bulgarian study, now out of print yet oft quoted by supplement makers, demonstrated that tribulus boosted blood levels of luteinizing hormone, a pituitary hormone responsible for regulating testosterone levels. Luteinizing hormone "turns on" natural testosterone production in humans. Researchers didn't study muscle strength, however. Because the study is out of print, it is impossible to verify important details such as how much luteinizing hormone levels increased and whether it increased testosterone.

Another study, first published in the Russian journal Farmatsiya and mentioned in the 1996 Muscle and Fitness article by James Wright, M.D., reported that 750 to 1,500 mg oral doses of tribulus administered daily for 30 to 60 days increased testosterone levels of men suffering from impotence and infertility.³ The increase was not clinically significant and, again, researchers were studying only whether testosterone levels increased. They did not examine changes in muscle strength.

Tribulus on Trial
Some supplement company researchers are concluding that tribulus can influence muscle strength based on the Bulgarian and Russian studies. The problem with making this jump is that it is unclear how long either luteinizing hormone or serum testosterone was elevated and how much variation occurred among study subjects. That is, did some men's levels increase a lot while others increased only a little? Did they all increase to the same extent? Unless an individual reaches pharmacological or above-normal levels of serum testosterone, increases in testosterone after taking tribulus may be meaningless. Thus, tribulus may lack the physiological punch to have a significant, long-term effect on testosterone levels.

To put it into perspective, serum testosterone levels also rise after a hard sprint workout or a weight session in the gym.

To get around this enormous obstacle, manufacturers are combining tribulus with other hormone supplements that purportedly enhance testosterone production. The steroid precursors DHEA (dehydroepiandrosterone) and androstenedione are promoted as testosterone enhancers, but they work differently than tribulus. Both DHEA and androstenedione provide the raw material for testosterone formation, while, as mentioned previously, tribulus increases luteinizing hormone levels and therefore may affect testosterone production.^1,3

Assuming a combination of the three works better than any one ingredient on its own, several supplement companies are producing "stacked" products that combine DHEA, androstenedione and tribulus. The manufacturers claim that each compound's testosterone-inducing effects have been studied separately and have all been shown to potentiate testosterone production to varying degrees and by various mechanisms. This is a stretch, however, since published research on stacked supplements is nonexistent. Whether these stacked products yield better results remains to be seen.

DHEA and androstenedione are potent male hormones, and people should be cautious about using them. Anyone taking either DHEA or androstenedione should have regular blood tests and discuss the therapy with a health care provider. The assumption that DHEA, androstenedione and tribulus are effective training aids for bodybuilding and fitness training is, at this point, sheer speculation.

Is It Safe?
No significant adverse effects in humans were noted in the three tribulus studies that have been conducted. However, pregnant or lactating women should avoid this product, as should children, since it has the potential to significantly alter hormonal chemistry. Men with enlarged prostates should consult their physicians before taking the herb. According to C.A.B. Enterprises, a tribulus importer based in Visalia, Calif., both acute and long-term studies in which rats were given more than 10 mg of tribulus per kg of body weight indicated extremely low toxicity.⁴

The bottom line? Despite the anecdotes, there is no conclusive evidence that tribulus enhances muscle growth or strength. For now, it is merely a fad. More research must be conducted on healthy people who have no libido or hormonal problems to see if tribulus truly affects muscle. It must be evaluated both as a stand-alone supplement and in combination with other supplements. And finally, the study results must be peer-reviewed.

Sidebars:
Buyer Beware
Further Reading

Edmund R. Burke, Ph.D. is an exercise physiologist at the University of Colorado, Colorado Springs. He is author of Optimal Muscle Recovery (Avery Publishing, 1999).

References

1. Yan W, et al. Phytochemistry 1996;42(5):1417-22.

2. Jayaram S, et al. Indian Drugs 1993;30(10):498-500.

3. Milanov, et al. Farmatsiya 1987;37(6):142.

4. Tribulus Gold, C.A.B. Enterprises, Visalia, Calif.