News · Longevity & Aging
Semen quality in 8,320 Danish men held steady across 26 years, with a small recent rise
The story of collapsing sperm counts rests mostly on pooled analyses. A Copenhagen program that has examined young men the same way every year since 1996 found no decline, and a lot of low readings.
- 8,320 young men examined in Copenhagen between 1996 and 2022, in the same laboratory, the same way.
- Semen quality stayed broadly flat rather than falling, with a modest improvement in the last five years.
- Median sperm concentration was 45 million per milliliter across the whole period.
- 36% of these men had at least one measurement below the World Health Organization reference level.
- This is one city's general population, not a global answer to whether sperm counts are falling.
Few health claims travel as easily as the collapse of sperm counts. The usual version has them halving in fifty years, heading for zero somewhere in the middle of this century, with plastics or pesticides or modern life to blame. It is a good story, and the evidence underneath it is thinner than the retelling suggests: most of it comes from pooling studies that used different men, different laboratories and different methods across decades.
Denmark has been running the antidote to that problem since 1996. Every year, young men in Copenhagen attending the compulsory assessment for military service have been invited to give a semen sample, analyzed in the same laboratory the same way. That now amounts to 8,320 men over 26 years, and the trend line does not fall.
Why measuring semen quality the same way for 26 years matters
The decline literature has a methods problem it cannot fully solve. If the 1970s papers counted sperm differently, recruited differently, or measured men with different reasons for being there, then a downward line across decades might partly be a change in how the counting was done.
A single program, one city, one laboratory, one recruitment route, removes most of that. It cannot tell you about the world, but whatever it finds about Copenhagen is a real change rather than a methodological one.
How the Copenhagen men were recruited
The design is unusual and the reason the cohort is worth attention. The data include results of annual examinations of a total of 8320 men included from the general population in relation to compulsory assessment for military service, rather than men who turned up at a clinic because something was wrong.
That distinction does most of the work. Fertility clinic samples are selected for having a problem, so they say nothing about a population. Men presenting for military assessment are, near enough, young men in general.
Each provided semen, urine and blood samples, completed a questionnaire and underwent a physical examination, and the team tracked trends by year of examination and by year of birth.
What the semen quality numbers showed
Two things, and they pull in different directions. The first is that the level is low. The median sperm concentration was 45 million/mL, total sperm count was 141 million, 61% progressively motile and 6.5% morphologically normal, and across the 26 years, 36% of participants had one or more semen parameters below WHO reference levels.
More than a third of ordinary young men, below reference on something. That is the finding that deserves the alarm, and it has been true the whole time.
The second is that it has not been getting worse. Semen parameters remained relatively stable, but a modest improvement was observed in the most recent period: sperm concentration rose from a median of 44 to 49 million per milliliter between the late 1990s and 2017 to 2022.
Why the testicular cancer line matters here
Sperm production and testicular cancer are thought to share a root, in how the testes develop before birth, which is why Danish researchers track them together. A marginal increase in sperm concentration appeared from the earliest to the latest birth cohorts, coinciding with a plateau following the previous increase in testicular cancer incidence among Danish men.
Two measures that should move together did move together. That is not proof of anything, but it is the sort of internal consistency that makes a flat trend easier to believe than a single reassuring number would be.
What 8,320 men in one city cannot settle
Copenhagen is not the world. Danish men are relatively affluent, the exposures they meet are European, and any country with different industry or diet could look different.
The authors are also careful about the upturn, and worth following: the modest improvement may reflect favorable changes in environmental exposures or lifestyle factors, potentially related to the COVID-19 period, and they note it should be interpreted cautiously as it may represent random variation. A five-year rise at the end of a 26-year series is exactly where chance is most likely to be mistaken for a trend.
Nor does any of this measure fertility. Semen quality is a laboratory number, and whether a couple conceives depends on both of them, on timing and on much else.
What to take from three decades of steady, low numbers
The frightening version of this story, the one about a straight line to zero, is not supported by the best-measured population available. That is worth knowing, because it is repeated constantly.
The less dramatic version is more troubling and better evidenced: a third of young men in a wealthy country have at least one semen measurement below the reference level, and that has held for a quarter of a century. MedlinePlus notes that infertility affects a substantial share of couples and that about one third of the time the problem is with the man. Nothing here says that is getting worse. It says it has been bad for a long time, and that stability is not the same as reassurance.
People also ask
What did the study find?
The median sperm concentration was 45 million/mL, total sperm count was 141 million, with 61% progressively motile and 6.5% morphologically normal spermatozoa. Semen parameters remained relatively stable, with a modest improvement in 2017-2022 compared with 1996-2000: median sperm concentration rose from 44 to 49 million/mL. Across the 26 years, 36% of participants had one or more semen parameters below WHO reference levels.
Are sperm counts falling or not?
Pooled analyses of many studies have reported a decline, and they are the basis of most headlines. This program measured the same population the same way for 26 years and did not see one, which is the kind of evidence that is hardest to explain away as a change in methods.
Who were the men?
Young men from the general population of Copenhagen, recruited in connection with the compulsory assessment for military service, rather than men attending a fertility clinic. That distinction matters, because clinic populations are selected for having a problem.
What does 45 million per milliliter mean?
It is a middling number. It sits above the World Health Organization's lower reference limit but well below what was once considered typical, and concentration alone does not determine whether someone can father a child.
Why mention testicular cancer?
Because the two have moved together in Denmark, and both are thought to reflect testicular development before birth. The recent flattening of semen quality coincided with a plateau in testicular cancer incidence.
Should a man have his semen tested?
Not routinely, and not because of this study. Testing belongs in the context of trying to conceive without success, usually alongside a partner's assessment. This is general information rather than medical advice.