Mon-Fri 9am-6pm PST
+1 (800) 686-5898
support@longevitybased.com
Mon-Fri: 9am-6pm PST
Castration, Longevity & Testosterone Therapy: What We Know
A recent study published in Nature showed that sterilization and castration, which have been practiced throughout history (including for centuries by the Koreans) were associated with longer lifespans in a variety of vertebrates, including zoo animals, rodents and some wild populations. There is also some historical human data from Korean court eunuchs, who apparently had significantly longer lives compared to men of comparable age and socio-economic status. While most people will not interpret this as a practical intervention for themselves, it is likely that many will ask if this kind of data should lead us to reconsider our current thinking regarding the role of testosterone in aging men. The answer is not a simple "yes" or "no". While the animal data is intriguing, there is considerable uncertainty regarding its translation to clinical recommendations for testosterone replacement therapy (TRT).
What the Study Actually Examined
The researchers included two major data sets in their study. One consisted of records from zoos. Many zoo animals are either sterilized or put on some form of hormonal birth control and their zoological institutions maintain accurate records of lifespan and cause of death. The researchers examined records from 117 different species of zoo animals. The second data set was a comprehensive review of published reports examining sterilization. The researchers identified 71 studies from 22 vertebrate species, from fish through to man. Across these two data sets, the researchers demonstrated that male sterilization was consistently associated with increased average lifespan. When comparing the duration of life of male zoo animals subjected to sterilization with those that were not, the researchers estimated that males subjected to sterilization lived approximately 10% longer on average. Similar trends were observed in the published reports.
What Was Most Surprising About the Results?
While it might be expected that the primary mechanism of increasing lifespan due to castration would be the reduction of chronic disease, particularly cardiovascular disease and diabetes, the data did not show this. Instead, the largest apparent gains in lifespan were associated with a decrease in mortality due to causes other than chronic disease. Because the latter includes many miscellaneous and poorly categorized causes of death, the findings create difficulties for interpreting the biological mechanisms responsible for the observed effects.
Why Timing May Matter
One of the most interesting findings in the study was that the magnitude of the increase in lifespan was greater when the castration occurred prior to puberty. The reason for the importance of the timing of castration is that prepubertal castration alters developmental programming. Prepubertal castration prevents the surge of testosterone that permanently alters aspects of growth, body composition, and endocrine signaling. The authors speculate that removing testosterone at an early age may alter growth hormone-related pathways, which are often implicated in the biology of aging. The authors suggest that dampening growth hormone signaling can result in alterations in physiology favoring maintenance and repair. This concept is analogous to other forms of longevity research focusing on growth and nutrient signaling pathways, including those involving the mTOR-related biology of model organisms.
Two Possible Mechanisms Behind Longer Lifespan
Reduced Risk Behavior
Lower testosterone levels can reduce aggressive behavior, mating competition, territorial conflicts, injuries and thus fatalities among males in many species. Reducing fatalities due to violence, accidents, or competition can increase average lifespan among males in a population.
Changes in Longevity-Related Signaling
Alternatively, testosterone may impact growth-related signaling pathways that determine long term aging trajectories, especially when modified before puberty. Such modifications can result in subsequent changes in metabolism, cellular stress responses, and repair mechanisms. These two mechanisms are not necessarily mutually exclusive. However, using longitudinal lifespan data alone makes it impossible to distinguish between them.
The Human Eunuch Data Suggests...and Cannot Prove
Historical data from Korean eunuchs, which often come up in discussions of testosterone and aging, indicate that eunuchs reportedly lived 14 to 19 years longer than comparable men. This is an impressive difference. However, this is an example of a dataset that can be easily misinterpreted.
Key Limitations Include:
- Incomplete data, since birth and death dates are known for only a portion of eunuchs
- Selection bias, since the data for which birth and death dates are known may not reflect the entire eunuch population
- Confounding variables due to differing living conditions, social protections and occupational roles
Regardless of whether the differences in lifespan between eunuchs and non-eunuchs were real, it does not follow that health outcomes were improved in every area. Another historical analysis of eunuch populations found evidence of osteoporosis, which is consistent with the expectation of severely depressed lifelong testosterone levels.
Why Low Testosterone Is Not a Free Longevity Strategy
The biggest problem with the overly simplistic conclusion that lower testosterone = longer life is that in contemporary clinical data, low testosterone is often a sign of poor health. Chronically low testosterone has been associated with:
- Increased Type 2 Diabetes risk
- Decreased bone density and increased osteoporosis risk in older adults
- Increased associations with all-cause mortality in several cohorts
It is possible that low testosterone contributes to these conditions, but it is equally possible that low testosterone is simply a marker of these underlying metabolic dysfunctions, chronic inflammation or illnesses. Therefore, the eunuch data and the cohort data can appear to be contradictory. They are not measuring the same thing.
Prepubertal Castration Alters Development.
Late-life low testosterone in contemporary adults is often tied to obesity, insulin resistance, disrupted sleep, medication side effects, and chronic disease.
What Does This Mean for TRT?
The practical issue is not whether eliminating testosterone extends life. The practical issue is when testosterone replacement therapy (TRT) is indicated and what to avoid. Two common mistakes are made.
Treating a Number Rather Than a Person
When a single testosterone level is measured in an asymptomatic patient without context, this should never drive treatment.
Chasing Supraphysiological Levels
Using testosterone to elevate serum levels above normal ranges can introduce risk with unclear benefits to longevity. Furthermore, suppressing testosterone in this way can obscure the underlying lifestyle factors that are typically the greatest contributors to suppression.
Therefore, a more conservative clinical approach would be:
- Reversible Causes First
- Verify Hypogonadism
- Prescribe when low testosterone is present and symptomatic
- Carefully Monitor After Therapy Begins
Where Lifestyle Fits In
Many lifestyle factors can significantly influence testosterone levels, and are therefore often a good place to begin.
Weight and Metabolism
Obesity is one of the most significant risk factors for low testosterone. According to some studies, the risk of having low testosterone is greatly elevated in men with a BMI >30.
Exercise
Both resistance training and aerobic training have been shown to promote healthy testosterone profiles and improve cardiometabolic risk, independent of testosterone. Additional context regarding the relationship between exercise and healthy aging is provided in the articles on resistance training and healthy aging.
Sleep
Sleep deprivation has been shown to suppress testosterone production, and has even broader negative effects on metabolism. To provide additional background information, please refer to the article on optimizing your sleep to improve your overall health.
When weight loss is difficult, anti-obesity drugs such as GLP-1-based agents can be considered as part of a plan to help improve metabolic function, which can then enable the recovery of endogenous testosterone production. Please see the article on micro-dosing GLP-1 for longevity.
Practical Takeaways
- Sterilization is associated with longer lifespan across many vertebrate species, but the underlying mechanisms are not fully understood.
- The most pronounced effects appear when castration occurs before puberty, which limits direct relevance to adult clinical decisions.
- Human eunuch data is compelling but incomplete and subject to potential bias.
- Low testosterone in modern adults is often a marker of underlying metabolic or health issues rather than a longevity advantage.
- Testosterone replacement therapy may be appropriate for individuals with confirmed hypogonadism and related symptoms, but it should not be used to pursue elevated levels or ignore root causes.
- Weight management, regular exercise, and adequate sleep are the most effective first-line strategies for supporting healthy testosterone and long-term health.
Summary
Testosterone replacement therapy may be appropriate for individuals with confirmed hypogonadism and related symptoms. However, it should not be used to pursue elevated levels beyond normal ranges or to overlook underlying causes of low testosterone. Focusing on weight management, regular physical activity, and adequate sleep remains the most effective first-line approach for supporting healthy testosterone levels and long-term health.