January 3, 2026

Are Testosterone Levels Declining? What the Data Shows

The narrative of a decrease in testosterone levels across generations has been growing for many years. As a result of these claims, concerns have developed regarding whether a widespread environmental or social cause has led to the decline of testosterone in the male population. These concerns are further compounded as low testosterone levels are linked to several serious health issues and conditions. Therefore, determining if a population-level concern exists based upon a true biological decline versus a measurement artifact is extremely significant.

Declines in testosterone are expected with age. In men, testosterone begins to decline at approximately 1-2% annually after the 30's. An age related decline in testosterone does not automatically indicate a health problem. Declines in testosterone that occur across generations would be indicative of a possible environmental or social cause. Low testosterone has been associated with the following: decreased bone density; reduced energy and mood changes; sexual dysfunction; and, increased risk for overall and cardiovascular mortality.

Therefore, if the trend is indeed real, it would necessitate a population level concern. However, if the trend is partially a measurement artifact, then the panic may be misdirected.

Why this matters

An early study published in 2007 analyzed blood samples from approximately 1500 men sampled at three time points between 1987 and 2004. The objective of the study was to determine how testosterone levels changed over time. The authors reported that testosterone appeared to be decreasing not only with age, but also with each subsequent year, suggesting that men of the same age had lower testosterone levels in the latter years than in the previous years. Other studies in different countries reported similar trends, including studies in Denmark and Finland, and additional analyses conducted in the United States suggested that the trend continued. The consistency of the results from the different studies throughout the world provided a basis for believing that this may be a global problem.

What early studies suggested

Several proposed reasons have been offered to explain the decline in testosterone, including: exposure to environmental toxins, such as pesticides; microplastics, which may lower testosterone levels in animals; and metals or other contaminants. While these potential contributing factors have been difficult to link directly to the observed population-level declines in testosterone, there is one factor that will undoubtedly decrease testosterone levels. Obesity. Body fat can lower testosterone levels through insulin resistance and other mechanisms, and low testosterone can contribute to weight gain, thus producing a positive feedback loop. Given the sharp increases in obesity rates globally, it is a clear candidate for explaining the declines in testosterone.

However, even if obesity does explain some of the declines, it cannot explain all of the declines.

When obesity did not explain the decline

A large-scale study conducted in Israel evaluated the testosterone results from over 100,000 men who underwent testing between 2006 and 2019. The authors determined that there was a decline in testosterone levels in the general population. However, during the time frame evaluated in this study, average BMI did not increase. Therefore, it is highly unlikely that obesity contributed to the total decline in testosterone in this dataset. A recent study conducted in the U.S. also found that testosterone decline was evident in men with normal BMI. At first glance, this would appear to suggest that there is an additional factor outside of body mass that affects testosterone.

A different explanation that changes the picture

A new analysis examined a fundamental aspect of the data: measurement techniques. Testosterone assays have evolved over time. Different testing methodologies can yield systematic differences in results, regardless of the actual level of the hormone being assessed. In other words, the test itself may contribute to the numbers. In the U.S. dataset used in multiple prior analyses, the researchers identified a specific issue that existed across five survey periods.

The first two survey periods utilized one testosterone measurement technique
The last three survey periods employed a different technique

The newer technique tended to yield lower readings.

When comparing the data over time, and adjusting for which technique was used, much of the apparent increase in low testosterone prevalence corresponds with the transition to the newer measurement technique.

The authors contend that the definition of low testosterone needs to be adjusted for the newer technique. When this adjustment is made, the increase in low testosterone prevalence virtually disappears.

This interpretation presents a straightforward alternative: some of the reported generational declines may be fictional.

Why this does not fully resolve the issue

This measurement explanation is applicable to U.S. datasets in which measurement techniques changed over time.

However, this explanation does not address the Israeli study as the authors reported using a consistent methodology throughout the study.

Additionally, the Israeli study has limitations that make generalizing to the broader population difficult. The men in the study were tested because their clinicians ordered the tests. Therefore, this is not a random sample of the general population.

If clinicians increasingly referred men for testing due to symptoms, increased awareness, changes in clinical practices, or shifting criteria for concern over time, the population undergoing testing may have changed in ways that produce an apparent decline.

Such a situation produces selection bias. The population undergoing testing may not represent the broader population at any given time.

What we can say with confidence

Whether or not the generational decline narrative is accurate or exaggerated, one fact remains.

Testosterone declines with age.

Therefore, it is still reasonable to focus on modifying the determinants of low testosterone that individuals control, particularly if symptoms or risk factors for metabolic disorders are present.

Practical ways to support healthy testosterone

Weight management

Weight loss is consistently recommended as a first line treatment to improve testosterone levels in obese men.

Exercise

Resistance training can raise testosterone levels and aerobic training can help maintain healthy testosterone levels. See resistance training and healthy aging for more information.

Sleep

Sleep duration and quality are critical. One small study demonstrated that restricting sleep to approximately 5 hours/night for multiple nights resulted in lower testosterone levels compared to rested controls. Additionally, meta-analyses support sleep as an important determinant of maintaining normal testosterone levels. For more information on this topic, see optimize your sleep for better health.

Supplements

The strength of the evidence supporting supplements is significantly lower than for weight loss, exercise, and sleep. One supplement mentioned above is trimethylglycine (TMG) or betaine.

Studies conducted in athletes and with exercise protocols have shown that TMG supplementation resulted in higher testosterone levels compared to placebo.

These results are not definitive, and the benefit of TMG may be dependent on training status, baseline nutritional intake, etc. Supplements should be viewed as optional and secondary to the foundational components of lifestyle. For more information, see what the science says about TMG supplements.

The four areas to focus on (in that order) are:

Weight management
Resistance training and aerobic training
Sleep quality
Supplements only if you have an actual reason for taking them and have realistic expectations

Key takeaways

As we get older, our testosterone levels naturally drop.
There is evidence to suggest claims about generational drops in testosterone levels may be partially based on changes in how we test for it.
While obesity can contribute to lower testosterone levels, it doesn’t account for all of the trends being reported.
Some larger studies have been influenced by changes in the assays used to test for testosterone and/or selection biases.
Individuals who manage their weight, stay active through regular resistance and aerobic training, and maintain quality sleep will likely see the greatest benefits from the most researched interventions.

Summary

That testosterone levels are plummeting across generations has been presented as an established fact. However, the data presents a less clear picture.

Much of what appears to be a declining trend may be due to improvements in measurement techniques and the manner in which populations are chosen for study.

This does not mean that testosterone-related issues do not exist. This simply means that the panic being expressed at the population level may be premature.

Regardless of whether or not there is a broader trend toward lower testosterone levels, there is no question that testosterone levels decrease with age, and that body fat, physical activity, and sleep quality are significant influences on both individual testosterone levels and the manifestation of related symptoms.

Research Sources

Filed in: Lifestyle

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