Testosterone is best known for its role in sexual health, but its effects extend far beyond libido. It plays an important role in maintaining muscle mass, bone density, mood, cognitive function, and overall metabolic health in both men and women. While testosterone is often viewed as a male hormone, declining levels can impact both sexes and are more common than many people realize, with estimates suggesting that testosterone deficiency affects anywhere from 10% to 40% of adults worldwide.
In men, testosterone levels typically begin to decline around age 40, decreasing by approximately 1% per year. Women also experience age-related decline in testosterone that continues throughout the postmenopausal years, which often receives less attention in clinical practice. Symptoms of low testosterone for both sexes can include fatigue, reduced motivation, poor concentration, loss of muscle mass, decreased bone density, low libido, and unfavorable changes in body composition.
The conventional treatment for low testosterone is testosterone replacement therapy (TRT). While TRT can be highly effective, it may not be appropriate for everyone and comes with potential drawbacks, including fertility suppression, elevated hematocrit, prostate-related concerns, skin-related reactions, and the need for ongoing treatment. As a result, there has been growing interest in non-hormonal approaches that support the body's natural testosterone production rather than replacing the hormone directly.
One compound gaining interest in this area is geranylgeraniol (GG). GG is a naturally occurring isoprenoid produced through the mevalonate pathway, the same pathway responsible for the synthesis of cholesterol and coenzyme Q10 (CoQ10). Sitting upstream of CoQ10 in this pathway, GG serves as an obligatory substrate for its synthesis, meaning the body cannot produce CoQ10 without GG. It is also found in foods such as annatto seeds, flaxseed, olive oil, and sunflower oil. Beyond its role as a CoQ10 precursor, GG appears to support bone health, glucose regulation, and steroid hormone synthesis.
Preclinical research has shown that GG can stimulate testosterone production through activation of the cAMP/protein kinase A signaling pathway. Additional in vitro and animal research suggests that GG may support the synthesis of both testosterone and progesterone. Because cholesterol serves as the precursor for all steroid hormones, GG's involvement in cholesterol metabolism and other important cellular processes provides a mechanism through which it may influence steroidogenesis. Importantly, GG appears to be well-tolerated, and toxicological evaluation has supported daily doses up to 406 mg, with no significant safety concerns reported.
A recently published clinical trial investigated whether GG supplementation could influence testosterone levels, CoQ10 status, and measures of overall and sexual health in healthy middle-aged adults. The study used an 18-week, single-group, crossover, placebo-controlled design. Participants between the ages of 40 and 65 completed eight weeks of placebo, followed by a two-week washout period and another eight weeks of supplementation with 300 mg per day of annatto-derived GG.
Over the course of the 18 weeks, thirty-four participants completed the trial. The average age was approximately 51 years, and women slightly outnumbered men. Blood samples were collected following an overnight fast at baseline and at weeks 8, 10, and 18. Several metrics were measured, including total testosterone, free testosterone, sex hormone-binding globulin (SHBG), and CoQ10 concentrations, in addition to validated health questionnaires. Compliance was high among the participants, and no major adverse events were reported.
Following the intervention, results showed GG supplementation did not significantly change total testosterone, free testosterone, or SHBG levels. However, among men with lower baseline testosterone levels (below 600 ng/dL), GG supplementation produced a statistically significant increase in total testosterone. Average testosterone levels increased by approximately 28 ng/dL, suggesting a meaningful response in this particular group. This effect was not observed in women or men with higher baseline testosterone levels. This may suggest that individuals who already produce adequate amounts of a hormone may have limited room for improvement, whereas those starting from lower levels may experience a greater response. Similar patterns have been observed with other nutritional, botanical, and pharmaceutical interventions aimed at supporting testosterone production.
Interestingly, while GG supplementation did not significantly increase CoQ10 levels, the researchers did observe a decline in CoQ10 during the placebo phase that remained stable during the GG phase. Because healthy adults typically maintain adequate CoQ10 status and tightly regulate its production, a significant increase was not expected in this trial. However, these findings suggest that GG may help maintain CoQ10 levels over time, making it particularly relevant for populations at greater risk of depletion, including older adults and individuals taking statin medications. The researchers of this clinical trial also evaluated changes in physical, mental, and sexual health using validated questionnaires, but found no significant differences between the placebo and GG phases. Considering that participants were generally healthy and functioning well at baseline, there may have been little opportunity for measurable improvements to occur during the relatively short intervention period.
Overall, these findings suggest that while GG is unlikely to produce dramatic increases in testosterone in healthy adults with normal hormone levels, its effects may be more meaningful in individuals with lower baseline testosterone, where there is greater room for improvement. Although testosterone replacement therapy remains an important option for some individuals, these findings demonstrate the potential role of non-hormonal, nutritional approaches as part of a broader strategy for supporting hormonal health, particularly for those who cannot or choose not to use TRT.
As with any single study, these findings reflect a limited body of evidence and should not be generalized to all populations. Larger studies in targeted groups, such as men with late-onset hypogonadism or individuals taking statins, will help clarify the long-term role of GG supplementation for supporting testosterone and maintaining CoQ10 status in aging adults.
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By Jesse Martin, MS
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