Study analysis · European Journal of Endocrinology · 2025
Men’s testosterone levels have been silently declining for 50 years—and it’s not just about age or weight.
A massive review of over a million healthy men found that testosterone levels have dropped significantly since 1971, even after accounting for age and BMI.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study is like looking at many measurements of testosterone in men over many years and seeing that on average, the numbers have gone down. But it doesn't prove that something specific, like pollution or stress, causes this drop because it's not an experiment where we change one thing and see the effect. It just shows that there's a pattern over time.
What’s the bottom line?
Scientists looked at many past studies about testosterone in healthy men and found that levels have been going down over the last 50 years.
How strong is this study?
This study is a big review that combined a lot of smaller studies, which gives it a huge amount of data, so the overall pattern is probably real. But because those smaller studies were not experiments, they might have differences in how they measured testosterone, and there could be other factors affecting the results, so we can't be sure what's causing the decline.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
0 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control groupno control group
- Sample sizeno sample size reported
- Follow-upno follow-up reported
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 533 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
This design cannot establish causation — the findings describe an association, not a cause. This is a systematic review and meta-analysis of observational studies (likely cross-sectional or cohort) examining temporal trends in hormone levels. Without randomization and control groups, causation cannot be established. The observed associations may be influenced by confounding factors (e.g., lifestyle, environmental exposures, assay variability) and reverse causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified in the provided text; no funding disclosure or author affiliations are mentioned.
The provided text is only an abstract and does not include a conflict of interest statement, funding declaration, or author affiliations. Without full text, we assume no declared conflicts. However, the absence of disclosure does not guarantee no conflicts exist; further information would be needed for a thorough assessment.
Key takeaways
- 01
From 1971 to 2024, testosterone levels decreased significantly even after accounting for age and weight.
- 02
LH (a hormone that controls testosterone) also went down, but another hormone called FSH did not.
- 03
This means that the average healthy man today has lower testosterone than his father or grandfather did at the same age, which might affect health and well-being.
Why this study matters
The Big Picture: Millions of Men, One Trend
This meta-analysis included 1,256 studies with over 1,064,891 healthy men, spanning from 1971 to 2024. After adjusting for sample size, age, and BMI, the researchers found a significant decline in testosterone levels over time (meta-regression coefficient -0.6, SE 0.2, p<0.001).
It's rare to have such a large dataset, making this trend hard to ignore. It suggests our environment or lifestyle is affecting our hormones on a population level.
Age and Weight Don’t Explain It
The decline persisted even after accounting for age and BMI, and BMI itself showed no significant temporal trend (p=0.617). This challenges the common belief that rising obesity rates are the main driver.
It shifts the blame away from obesity and points to other factors like environmental chemicals, stress, or sedentary lifestyle.
The Brain Connection: LH Drops, FSH Doesn’t
Luteinizing hormone (LH), which signals the testes to produce testosterone, also declined significantly (-0.1, SE 0.1, p<0.001), while follicle-stimulating hormone (FSH) showed no trend (p=0.143). The parallel drop in LH suggests the hypothalamus-pituitary axis may be resetting.
This gives a clue: the problem might be in the brain, not just the testes, possibly due to environmental endocrine disruptors.
What’s Causing This? Lifestyle or Environment?
The authors hypothesize that changing environmental exposures or lifestyle factors are likely responsible, but the abstract doesn't specify which. This opens the door for further research.
It raises awareness about potential toxins, diet, stress, and other modern factors that we might not think about.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists looked at many past studies about testosterone in healthy men and found that levels have been going down over the last 50 years.
Research results
From 1971 to 2024, testosterone levels decreased significantly even after accounting for age and weight. LH (a hormone that controls testosterone) also went down, but another hormone called FSH did not.
What this means - more context
This means that the average healthy man today has lower testosterone than his father or grandfather did at the same age, which might affect health and well-being.
Investigate the existence of a temporal trend in serum testosterone levels among healthy men.
A systematic review and meta-regression of 1,256 articles (1,504 study groups, 1,064,891 healthy men) found a significant decline in serum testosterone levels from 1971 to 2024, independent of age and BMI. Luteinizing hormone also declined significantly, while follicle-stimulating hormone showed no significant trend. The parallel decline suggests a possible resetting of the hypothalamic-pituitary-testicular axis.
Methods Used
Systematic literature search covering studies from 1971 to July 2024, including only healthy adult men (≥18 years) with no conditions affecting testosterone. Meta-regression analysis adjusted for study sample size, age, BMI, assay type, and environmental/demographic data.
Main Finding
Serum testosterone levels declined significantly over time (meta-regression coefficient -0.6, SE 0.2, p<0.001) after adjusting for sample size, age, and BMI. LH also declined (coefficient -0.1, SE 0.1, p<0.001), while FSH showed no significant trend (p=0.143). BMI showed no temporal trend (p=0.617).
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Publication bias not addressed
- •Heterogeneity among included studies not reported
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 533 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Human Meta-Analysis
Subject
Lower probability
on the GRADE evidence scale
This study is like looking at many measurements of testosterone in men over many years and seeing that on average, the numbers have gone down. But it doesn't prove that something specific, like pollution or stress, causes this drop because it's not an experiment where we change one thing and see the effect. It just shows that there's a pattern over time.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Large sample size (1,064,891 subjects) from 1,504 study groups
- Comprehensive systematic search covering over five decades
- Meta-regression adjusting for age, BMI, sample size, and assay method
Weaknesses
- Full methodology not available - based on abstract only
- Observational design of included studies cannot control for all confounders
- Potential heterogeneity across studies in assay techniques, population selection, and measurement timing
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists looked at many past studies about testosterone in healthy men and found that levels have been going down over the last 50 years.
Research results
From 1971 to 2024, testosterone levels decreased significantly even after accounting for age and weight. LH (a hormone that controls testosterone) also went down, but another hormone called FSH did not.
What this means - more context
This means that the average healthy man today has lower testosterone than his father or grandfather did at the same age, which might affect health and well-being.
Investigate the existence of a temporal trend in serum testosterone levels among healthy men.
A systematic review and meta-regression of 1,256 articles (1,504 study groups, 1,064,891 healthy men) found a significant decline in serum testosterone levels from 1971 to 2024, independent of age and BMI. Luteinizing hormone also declined significantly, while follicle-stimulating hormone showed no significant trend. The parallel decline suggests a possible resetting of the hypothalamic-pituitary-testicular axis.
Methods Used
Systematic literature search covering studies from 1971 to July 2024, including only healthy adult men (≥18 years) with no conditions affecting testosterone. Meta-regression analysis adjusted for study sample size, age, BMI, assay type, and environmental/demographic data.
Main Finding
Serum testosterone levels declined significantly over time (meta-regression coefficient -0.6, SE 0.2, p<0.001) after adjusting for sample size, age, and BMI. LH also declined (coefficient -0.1, SE 0.1, p<0.001), while FSH showed no significant trend (p=0.143). BMI showed no temporal trend (p=0.617).
Confidence Level
Limited - based on abstract only, full methodology not available
Study Flags
Red Flags
- •Full text not available - methodology details cannot be verified
- •Publication bias not addressed
- •Heterogeneity among included studies not reported
No biological mechanisms were identified in this study. This may be an epidemiological, observational, or survey-based study that reports associations rather than proposing causal biological pathways.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 533 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Human Meta-Analysis
Subject
Lower probability
on the GRADE evidence scale
This study is like looking at many measurements of testosterone in men over many years and seeing that on average, the numbers have gone down. But it doesn't prove that something specific, like pollution or stress, causes this drop because it's not an experiment where we change one thing and see the effect. It just shows that there's a pattern over time.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Large sample size (1,064,891 subjects) from 1,504 study groups
- Comprehensive systematic search covering over five decades
- Meta-regression adjusting for age, BMI, sample size, and assay method
Weaknesses
- Full methodology not available - based on abstract only
- Observational design of included studies cannot control for all confounders
- Potential heterogeneity across studies in assay techniques, population selection, and measurement timing
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
This study is a big review that combined a lot of smaller studies, which gives it a huge amount of data, so the overall pattern is probably real. But because those smaller studies were not experiments, they might have differences in how they measured testosterone, and there could be other factors affecting the results, so we can't be sure what's causing the decline.
0 / 100
- COI disclosureconflicts of interest not disclosed
- Data availabilitydata not shared
- Code availabilitycode not shared
0 / 100
- Randomizationrandomization unclear
- Blindingblinding unclear
- Control groupno control group
- Sample sizeno sample size reported
- Follow-upno follow-up reported
100 / 100
54 / 100
- P-values+15/15
- Effect size+20/20
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 533 / 100
Probability of being correct
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
This design cannot establish causation — the findings describe an association, not a cause. This is a systematic review and meta-analysis of observational studies (likely cross-sectional or cohort) examining temporal trends in hormone levels. Without randomization and control groups, causation cannot be established. The observed associations may be influenced by confounding factors (e.g., lifestyle, environmental exposures, assay variability) and reverse causation.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified in the provided text; no funding disclosure or author affiliations are mentioned.
The provided text is only an abstract and does not include a conflict of interest statement, funding declaration, or author affiliations. Without full text, we assume no declared conflicts. However, the absence of disclosure does not guarantee no conflicts exist; further information would be needed for a thorough assessment.