Yves here. All around the world, there is ample evidence of human activity level exceeding what the planet can support, from an huge level of species die off to global warming induced wild weather changed to severe air pollution in large cities across Asia to endemic microplastics pollution. So the idea that birth rates are falling in high-resource-consuming countries ought to be treated as a welcome development, and one that can be managed as robotics and (we are told) AI will greatly reduce labor needs and thus alleviate if not completely end the classic bugaboo of rising dependency levels, as in fewer workers relative to the total population. But oh noes! That like so many things would take industrial policy, which advanced economies have foresworn.
Unfortunately, the Trump Administration and the snake oil salesman installed as HHS chairman RFK, Jr. in particular are making the possibility of a “Let’s make America whiter” campaign running up against low reproduction rates among the non-Hispanics and the effort to choke off immigration. The US was forecast to show a fall in population as of the 2000 census; it was both 1990s immigration and higher birth rates among Hispanics that produced the unexpected rise.
Of course, there is another level to this issue, of advanced (and even middle ranking, see Thailand) relying on immigration for lower-wage labor and to bolster growth as native population increases stall out. Most developed economies, unlike the US during its very large later 1800s-early 1900s immigration wave, are not doing much to assist in assimilation. That means the newcomers are much more visibly alien, stoking not-uncommon tendency towards tribalism and rejection of out-groups. And of course businesses want immigration to suppress wage rates, so unless there are very strong worker protections, laborers have a legitimate beef.
And with the public expecting more and more from medicine, the level of press coverage of fertility treatments and surrogacy suggests that more prospective parents who have difficulty conceiving doggedly pursue treatments rather than adopting.
My beef with articles like starts with the headline, which in fairness reflects Administration hobbyhorses. Falling male fertility is a big deal as a health issue. It should highlight concerns about population-wide factors that are damaging virility, from depression (which is correlated with lower sperm counts) to diet to pollutants. I am amazed by occasional reports of the level of medications and recreational drugs in public water supplies, with no discussion of whether there is an affordable way to reduce their level. That’s one indicator of pervasive public health negligence. Even if there are no easy answers, I don’t see the question being entertained.
By Joshua Cohen, an independent health care analyst and freelance writer based in Boston, and the author of Undark’s Cross Sections column. Originally published at Undark
For decades, U.S. marriage rates have been on the decline while the average age at which Americans have children has risen. Alongside this, birth rates have dropped — a phenomenon the Health and Human Services Secretary Robert F. Kennedy, Jr. has called a “national security threat.” Within Donald Trump’s administration’s Make America Great Again movement, pro-natalists opine that society’s existence could be at stake.
Kennedy issued a warning at a White House press briefing in October, arguing that the fertility rate is not high enough to ensure the American population remains stable. The rate dropped to a historic low in 2023 and continued to slide in 2024. The total fertility rate that year was less than 1.6 live births per woman of childbearing age. This is well below the replacement rate of 2.1<, at which population size remains constant from generation to generation. Many women are proactively choosing to have no or fewer children. But for those who do wish to get pregnant, yet struggle with infertility, President Trump has announced that he will work with a drugmaker to offer several fertility medications at a heavy discount and make it easier for employers to offer fertility benefits.
The administration has not, however, spoken publicly about specific treatments geared toward men. And until recently, the topic of male infertility was somewhat taboo, even though it plays a role in roughly half of all cases in which a woman struggles to get pregnant.
A man’s age, health, and weight can all contribute to infertility. Research suggests this is because these variables influence sperm count and testosterone levels — both of which appear to be on the decline. Kennedy has repeatedly expressed alarm about these declines, with exaggerated claims such as this, from an October press event: “Today, the average teenager in this country has 50 percent of the sperm count, 50 percent of the testosterone as a 65-year-old man.”
But what role does male biology play in declining birth rates? Could addressing this help the administration meet its fertility-boosting goals? The answer, it turns out, is complicated.
Over the years, researchers have asked if sperm counts really are on the decline. More recently, one group developed what some critics now call the “sperm count decline hypothesis,” which posits that sperm counts are falling and that a low sperm count is an indicator of sub-optimal health, which could impact fertility.
A 2017 meta-analysis, for example, based on data from North America, Europe, Australia, and New Zealand, foundthat sperm count had declined by 52 percent between 1973 and 2011. A follow-up in 2022 by some of the same authors showed a similar reduction across an even wider range of countries. Rossella Cannarella, a clinician and researcher at Italy’s University of Catania who was not involved in either study, told Undark that the findings track with the results of her own research and with what she sees in patients in her clinical practice. She attributes the lessening in sperm count to pollution and metabolic disorders such as obesity, among other things.
In a newly released report for the Health and Environment Alliance, an EU-based not-for-profit, Cannarella warns of the dangers of chemical pollution in fueling a “growing male health crisis.” This includes male infertility — with evidence suggesting a possible association with exposure to harmful chemicals and other so-called endocrine disruptors. These are natural or synthetic substances found in plastics, food packaging, and pesticides that can interfere with hormones such as estrogen, testosterone, and thyroid. Notably, at that October White House press briefing, Kennedy emphasized the possible role of endocrine disruptors in the fertility rate decline.
Endocrine disruption is posited to take place through exposure to substances in the air, food, and water, as well as through the skin. Endocrine disruptors in food can impact the beneficial microbes living in a person’s gut. Germar Pinggera, a clinician and researcher at the Innsbruck Medical University, told Undark that pollution, poor diet, and an imbalanced microbiome can be detrimental to sperm production, as well as sperm quality. These factors, he suggests, may all be affecting fertility.
At the same time, Pinggera said that while some studies point to a decrease in sperm count, “there are still other data that aren’t confirming that.”
In a press release, the lead author of a recent meta-analysis suggested that among men in the U.S. with no known fertility challenges, “sperm counts are largely stable and haven’t changed significantly” in recent years. Moreover, it’s unclear whether sperm quality has declined. According to a 2022 review published in Nature Reviews Urology, researchers have observed a trend in some geographic areas, but available data doesn’t indicate that semen quality is necessarily deteriorating worldwide or in the Western world.
Furthermore, a reevaluation of the 2017 meta-analysis cited above suggests there could be issues with respect to how sperm counts were measured. Researchers identified inconsistencies in the sperm count decline hypothesis and proposed an alternative framework that asserts that sperm count varies within a wide range, much of which can be considered normal.
Critics of the sperm count decline hypothesis also contend that it takes for granted that sperm count is an accurate predictor of male fertility. Experts disagree about what exactly the fertility implications are of a reduced sperm count. Male fertility involves multiple components, including sperm count, concentration, shape, and motility, in addition to testosterone levels, age, and other characteristics. And male fertility can’t be seen independently from female fertility, say, in the context of a couple trying to conceive spontaneously or with assistive reproductive technologies. Here, it’s essential to evaluate the interactions between sperm, the female reproductive tract, and the egg.
What about the role of testosterone, the hormone responsible for changes that occur in boys during puberty, including production of sperm and the maintenance of certain biological functions related to reproduction in adult men? Levels of testosterone generally peak during adolescence and early adulthood. As a male ages, his testosterone level gradually diminishes — typically around 1 percent annually after age 30 or 40.
Testosterone is essential for sperm production, but it isn’t the only necessary ingredient. Other hormones are also involved, including luteinizing hormone — which stimulates testosterone production — and follicle-stimulating hormone, making it difficult to parse the precise role each hormone plays in infertility.
And while Kennedy has asserted that young men’s testosterone levels have plummeted over the decades, the scientific literature tells a more nuanced story. A 2021 publication, for example, found that testosterone levels have diminished among young adult males from 1999 to 2016 by around 25 percent. Further, researchers observed that among adolescent and young adult males, testosterone deficiency is 20 percent.
Still, Geoff Werstuck, a professor at McMaster University in Ontario, wrote in an email to Undark that the “relative speed of the decline is absolutely noteworthy.” An endocrinologist from the Cleveland Clinic also pointed to the accelerated decline in testosterone and appeared to link it to a similar set of elements likely causing a reduction in sperm count.
But not everyone agrees about the extent of the decline. Adith Arun, a researcher at the Center for Outcomes Research and Evaluation at Yale New Haven Hospital, wrote in an email to Undark that a shift occurred over time in terms of measurement techniques that makes it hard to make firm comparisons. The cutoff for low total testosterone was not updated to account for use of these new techniques. In a follow-up email, he noted that this may in turn “result in overstating the fraction of self-reported healthy individuals with low total testosterone values.”
And Werstuck noted that “because of a lack of good historical data” it’s difficult to determine when the testosterone downturn began and “precisely how large the effect is.” He also said that he doesn’t believe there is “strong data to support or discount” the various factors that have been hypothesized as causing the trend.
All of this means that the exact role of male biology in declining birth rates is unclear.
At a discussion in August organized by the Harvard University T.H. Chan School of Public Health, one panelist said that much of the decline comes from teenagers and young women delaying childbearing. The expert, Margaret McConnell — an associate professor of in the Department of Global Health and Population at Harvard University — cautioned that aggregate family size over a woman’s lifetime has not fallen nearly as pointedly as the annual fertility rate.
“We’re seeing this as part of an ongoing process of fertility delay” Leslie Root, a fertility and population policy researcher at the University of Colorado Boulder, told Newsweek. “We know that the U.S. population is still growing, and we still have a natural increase — more births than deaths.”
The “ongoing process of fertility delay” that Root refers to may partially reflect reproductive agency. Women can make informed decisions about their reproduction that in turn depend on a host of factors that include their career paths, ability to afford raising a family, and technological advances such as IVF and egg-freezing. These can influence the age at which individuals marry, preferences regarding family size, and the general reproductive behaviors in women and men in American society.
And so, despite the panicked rhetoric about fertility and sperm counts, there remain a host of unresolved questions, many of which extend beyond the realm of science into social factors.
