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By Jasmine Laws
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Health Secretary Robert F. Kennedy Jr. told a White House press briefing that the declining U.S. fertility rate is a "national security threat" and warned it is not high enough to ensure the American population remains stable.
Kennedy was speaking to the press after President Donald Trump announced his administration had struck a new deal to reduce the costs of fertility medication.
"Secretary Kennedy is sounding the alarm on a public health issue others are too timid, or too politically cautious, to confront," a Department of Health and Human Services (HHS) spokesperson told Newsweek.
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Why It Matters
Fertility rates have become a global concern, and the Trump administration has made it a key focal point of its policies. According to the Centers for Disease Control and Prevention (CDC) data, U.S. fertility hit a new low in 2024, after steadily decreasing over the last decade.
Lower fertility rates have been associated with a wide range of economic implications, such as long-term economic stagnation and a reduction in innovation, according to the non-partisan research center, the Centre for Economic Policy Research.
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What To Know
During the briefing, the Health Secretary also said the average teenager has "50 percent of the sperm count, 50 percent of the testosterone as a 65-year-old man," while girls are "hitting puberty six years early," which he said was "bad."
The HHS spokesperson told Newsweek that "a growing body of peer-reviewed research shows significant declines in sperm counts over the past decades, and pretending this isn’t a serious trend is irresponsible."
They shared various studies with Newsweek, referring to the secretary's comments, including studies showing a significant decline in sperm count across North America, Europe, Australia and New Zealand—though these studies did not evaluate the difference in sperm count between teens and older men.
"Secretary Kennedy is focused on the big picture: rising chronic disease, endocrine disruption, and declining reproductive health. The data is real, the stakes are high and ignoring it doesn’t make it go away," the spokesperson said.
Girls hitting puberty earlier has been documented in various studies, with some research suggesting that an increase in obesity could be playing a role in the shift, as well as environmental factors and even compounds used in scented personal care products and household items.
Whether girls are reaching puberty six years earlier than previously is debatable—a 2024 study found a shift of only six months, not six years.
This is not the first time Kennedy has commented on the subject—in April, on Fox News' Jesse Watters Primetime during a discussion on the effects of food additives, he said that girls are "hitting puberty six years early."
In regard to male sperm count and testosterone, while some studies indicate a decline in testosterone levels in men more broadly across the American population, research from last year found they have remained stable.
Newsweek was also not able to find research confirming that teenage boys have less testosterone than 65-year-old men.
"Sperm declines with age, so teenagers and young men most certainly have a higher sperm count than older men," Karen Guzzo, director of the Carolina Population Center and professor of sociology at the University of North Carolina at Chapel Hill, told Newsweek.
The decline in birth rates and overall population in America is caused by many factors, such as the expense and limited availability of childcare, access to family leave, and greater educational and employment opportunities for women, leading to later marriage and delayed childbearing.
It is also a result of the decline in the number of teen births and people having children in their early 20s—births that are often unintended—and Guzzo said the drop in birth rates is not because of "changes in sperm counts."
The decline in fertility and birth rates is of great concern to the Trump administration and has been something the president has commented on throughout his second term.
On whether this poses a "national security threat," Guzzo said that she believed this view "stems from some notion that population size is a primary driver of political and military power on the global setting."
However, she said that the American population is projected to continue to grow for the next three decades, and that it would be "growing for an even longer period of time if the U.S. was not engaging in mass deportation and discouraging immigration."
She added that U.S. military spending "far outranks its peer nations, so our national security seems pretty strong."
On Thursday, Trump announced a deal with the drugmaker EMD Serono to reduce the cost of a commonly used fertility medication—Gonal-f, an expensive, hormonal-based drug that helps to trigger ovulation, which is one of the drugs used during in vitro fertilization (IVF).
This comes after Trump signed an executive order in February aiming to reduce the cost of IVF, a medical procedure that helps people facing infertility have children.
What People Are Saying
President Donald Trump said: "We want to make it easier for all couples to have babies, raise children and start the families they have always dreamed about."
HHS Secretary Robert F. Kennedy Jr. said: "When my uncle was president, the fertility rate in this country was 3.5 percent. Today, it is 1.6 percent. The replacement rate, in other words the amount of fertility that you need in order to keep your population even, is 2.1 percent. We are below replacement right now. That is a national security threat to our country and we know why this is happening, and President Trump is addressing the root causes through his MAHA agenda of reducing endocrine disruptors, the exposure to chemicals that decrease fertility."
Guzzo told Newsweek: "The decline in U.S. fertility started happening around the Great Recession. That decline has largely been due to declining births to women in their teens and early 20s, which is generally good news since many of these births would have been unplanned and occurring to women who themselves would say those births didn’t happen at the right point in their lives. But, birth rates at older ages are not rising enough to offset those declines in birth rates at younger ages even though births to women in their late 30s and early 40s are rising."
She said: "What people are doing is postponing having children because they feel they do not have the right circumstances to have a child, or have another child. Economic factors play a large role in this, with the cost of living, housing, student loan debt, and childcare being important considerations. When they don’t feel confident about their future, they try to avoid getting pregnant now, usually in the hopes that things will be better at some future time point."
She added: "Low birth rates mean the population is aging, with shifts in the size of the older population relative to the younger population. It changes the size of the future labor force. It alters the future tax structure, which has implications for Social Security."
Kasey Buckles, a professor of economics at the University of Notre Dame, told Newsweek: "The evidence on trends in sperm counts in general is extremely mixed, and for teenagers we know even less. But teenagers have always had lower sperm counts than adults, because they have not fully matured. The idea that girls are starting puberty six years earlier is unfounded and nonsensical—this would mean that a typical girl today would start puberty at around six years old (as the average age in the 1950s was around 12). That is simply not happening."
She added: "It is true that a big reason that fertility in the U.S. has declined in the last 15 years is because we have seen a huge drop in births to young people—especially teenagers. The teen birth rate has fallen 70 percent since 2007. I think most people view that as a good thing, and we know it is because teenagers are having less risky sex, and because access to effective methods of contraception like IUDs has increased for teen girls. Declining sperm counts for teen boys are unlikely to be playing an important role in this positive development."
What Happens Next
Scientists are continuing to investigate the causes and consequences of earlier puberty in children, and the decline in fertility in America more broadly.
This article contains reporting from the Associated Press.
Update 10/17/25, 10:41 a.m. ET: This article was updated with comments from Karen Guzzo and Kasey Buckles and with additional information.
Update 10/17/25, 12:26 p.m. ET: This article was updated with comments from the Department of Health and Human Services.
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