Your Testosterone Isn't Just Declining With Age. It's Declining Across Generations.
A 45-year-old man today, at his current age, likely has lower testosterone than a 45-year-old man measured in the 1980s did at the same age. Not because he's sicker, not because he's heavier, and not because "45 just hits different now." Something is shifting at the population level, across birth cohorts, independent of any individual man's health or habits, and it's been documented for almost two decades.
Most men have never heard this. What they've heard instead is some version of "your labs are normal," delivered with a shrug. This post is about why that reassurance rests on a moving target.
The Reference Range Itself Moved
In July 2017, LabCorp, the largest clinical lab in the country, lowered its normal reference range for total testosterone in adult men from 348–1,197 ng/dL to 264–916 ng/dL. That's not a rounding error. A man who tested at 320 ng/dL in 2016 was below the normal range. The same man, same number, tested in 2018, was inside it.
The change came from a large harmonization study that pooled data from over 9,000 men across four major cohorts in the US and Europe, cross-calibrating different labs' assays against a single reference standard so results could be compared apples-to-apples (Travison TG et al., Journal of Clinical Endocrinology & Metabolism, 2017 — PMID: 28324103). That study wasn't trying to measure a population decline; it was solving a real and separate problem, that different labs' testosterone assays didn't agree with each other. But one of its consequences was a new, lower "floor" for what counts as normal, adopted industry-wide.
Normal labs don't guarantee a normal tissue response, and in this case, the definition of "normal" itself has shifted in the last decade.
The Decline Predates the Reference Range Change
The reference range change didn't create the decline. It responded to one that researchers had already been documenting for years.
The first major demonstration came from a 2007 study that measured testosterone in the same population of men, aged 45 to 79, at three different points in time, 1987–89, 1995–97, and 2002–04. The finding: a 60-year-old man measured in 2003 had meaningfully lower testosterone than a 60-year-old man measured in 1988, and the decline held even after statistically accounting for changes in weight, smoking, and other explanatory factors the researchers could measure (Travison TG et al., Journal of Clinical Endocrinology & Metabolism, 2007 — PMID: 17062768).
That same year, a separate Danish study looking at population surveys found a similar age-independent decline in more recently born men. The testosterone decline was statistically significant on its own, but lost significance once the researchers adjusted for the concurrent rise in average body weight across the same time period. SHBG, the protein that carries testosterone in the blood, remained significantly changed even after that adjustment (Andersson AM et al., Journal of Clinical Endocrinology & Metabolism, 2007 — PMID: 17895324). This study's testosterone finding may be partly explained by rising obesity; its SHBG finding wasn't.
Three More Populations, Three More Confirmations
If the Danish finding stood alone, obesity would be a reasonable full explanation. It doesn't stand alone.
A Finnish study spanning three national health surveys, conducted in 1972, 1977, and 2002, found a significant decline in both total and free testosterone in more recently born men compared to earlier-born men of the same age (Perheentupa A et al., European Journal of Endocrinology, 2013 — PMID: 23161753). Finland was expected to be an exception, given comparatively strong markers of male reproductive health in prior research. The decline showed up anyway.
An Israeli study of over 102,000 men tested between 2006 and 2019 found a highly significant, age-independent decline in testosterone across nearly every age group, and the authors stated directly that the decline was unlikely to be explained by increasing rates of obesity in their population (Chodick G, Epstein S, Shalev V, Reproductive Biology & Endocrinology, 2020 — PMID: 32151259).
And in 2025, the largest analysis of its kind pooled data from over 1,500 study groups and more than one million men, spanning studies published between 1971 and 2024. It found a statistically significant negative trend in testosterone levels across five decades, and the trend held up after adjusting for age, BMI, and assay method. The same analysis found that luteinizing hormone, the pituitary signal that tells the testes to produce testosterone, is declining in parallel, which points toward something happening upstream, at the level of hormonal signaling itself, not simply a testicular problem (Santi D et al., Journal of Endocrinological Investigation, 2025 — PMID: 40748419).
Why This Matters for the Conversation You're Actually Having
None of this means every man with low energy or low libido has clinically low testosterone, and none of it is a case for a specific treatment. What it does mean is that "your labs are normal" is a less settled statement than it sounds like.
A reference range built from today's population includes today's population-wide decline baked into it. If the average is lower than it used to be, "average" stops being a synonym for "healthy" or "optimal", it just means "common." A man who feels the way his father did at the same age, but whose lab number sits comfortably mid-range on a scale that has quietly shifted downward over two decades, is being compared to a different standard than his father was.
A Familiar Pattern
A patient in his mid-40s came in describing a gradual loss of drive and recovery capacity over about three years, nothing dramatic, just a steady erosion he'd mostly attributed to being busier and older. A prior physician had checked his testosterone, found it within the standard reference range, and moved on. Looking at where his number actually sat within that range, and discussing how that range itself had shifted since he was in his 20s, reframed the conversation from "your labs are fine" to "your labs are common, let's talk about whether common is what you're aiming for."
Who Should Have This Conversation
This is relevant for any man who has been told his testosterone is "normal" without being shown where in that range he actually falls, or without anyone mentioning that the range itself has moved. It's also worth a second look if it's been several years since your last check, given how much both individual levels and the reference range itself can shift in that time.
What a Realistic Timeline Looks Like
A full evaluation starts with more than a single total testosterone number, it includes free testosterone, SHBG, and a symptom history, since two men with identical total testosterone can have very different amounts actually available to their tissues. From there, next steps depend entirely on the individual picture, there's no default protocol that applies to everyone. Ongoing lab monitoring is part of any treatment plan, for as long as treatment continues.
If you've been told your labs are normal but you don't feel like yourself, that reference range may be measuring something different than what you'd assume.
Has anyone ever explained to you where in the "normal" range your own results actually fell?
A free consultation is a good place to start that conversation, no commitment required.
— Dr. Darrell Wilcox | @wellnessdoc_4everyoung on Instagram
References
Travison TG, Araujo AB, O'Donnell AB, Kupelian V, McKinlay JB. A Population-Level Decline in Serum Testosterone Levels in American Men. Journal of Clinical Endocrinology & Metabolism. 2007;92(1):196-202 — PMID: 17062768.
Andersson AM, Jensen TK, Juul A, Petersen JH, Jørgensen T, Skakkebæk NE. Secular Decline in Male Testosterone and Sex Hormone Binding Globulin Serum Levels in Danish Population Surveys. Journal of Clinical Endocrinology & Metabolism. 2007;92(12):4696-4705 — PMID: 17895324. (Testosterone finding lost significance after BMI adjustment; SHBG finding remained significant.)
Perheentupa A, Mäkinen J, Laatikainen T, Vierula M, Skakkebæk NE, Andersson AM, Toppari J. A Cohort Effect on Serum Testosterone Levels in Finnish Men. European Journal of Endocrinology. 2013;168(2):227-233 — PMID: 23161753.
Chodick G, Epstein S, Shalev V. Secular Trends in Testosterone — Findings From a Large State-Mandate Care Provider. Reproductive Biology & Endocrinology. 2020;18:19 — PMID: 32151259.
Santi D, Spaggiari G, Furini C, Griseta V, Zizzi EA, Granata ARM, Simoni M. Temporal Trends in Serum Testosterone and Luteinizing Hormone Levels Indicate an Ongoing Resetting of Hypothalamic-Pituitary-Gonadal Function in Healthy Men. Journal of Endocrinological Investigation. 2025;48(11):2721-2734 — PMID: 40748419.
Travison TG, Vesper HW, Orwoll E, Wu F, Kaufman JM, Wang Y, Lapauw B, Fiers T, Matsumoto AM, Bhasin S. Harmonized Reference Ranges for Circulating Testosterone Levels in Men of Four Cohort Studies in the United States and Europe. Journal of Clinical Endocrinology & Metabolism. 2017;102(4):1161-1173 — PMID: 28324103.
This content is for educational purposes only and does not constitute medical advice. Testosterone levels and treatment decisions vary by individual health history, symptoms, and lab findings. Any decision to pursue evaluation or treatment should be made individually with a qualified physician after a full evaluation. Individual results vary, and no outcome is guaranteed. Dr. Wilcox is licensed to practice in Texas, Arizona, Colorado, Oregon, and Florida.
