Why is RFK Jr. so worried about sperm count?

We spoke to experts about Kennedy’s claims about sperm and fertility — including the author of the study he cited.

This story was originally reported by Mariel Padilla and Jennifer Gerson of The 19th. Meet Mariel and Jennifer and read more of their reporting on gender, politics and policy.

Secretary of Health and Human Services Robert F. Kennedy Jr. has, historically, been very public about his concerns about what is plaguing the nation’s well-being. His long, complicated history with vaccines is well-documented. So is his long-standing spat with fluoride. Unlike President Donald Trump, he is not a fan of fast food, but he is a big believer in animal protein and raw milk.

And this week, he spoke about another issue vexing him: men’s sperm count. 

“The fertility crisis for women began in 2007; for men in 1970. Men had twice the sperm count as our teenagers do today. This is an existential crisis for our country. We had a series of presidents who were trying to discourage childbirth and motherhood in this country. We now have a president who is trying to encourage it,” Kennedy said at a White House event on maternal health Monday. 

While many experts agree that sperm counts are likely lower than they were decades ago, it is less clear how much influence a declining sperm count has on the country’s falling birth rate.

What the science says

Dr. Hagai Levine, the lead author the study Kennedy referenced and chairman of Israel’s association of public health physicians, said he agrees with Kennedy’s characterization that there is a “crisis.”

“I truly believe based on the data that there is a male fertility crisis globally and in the U.S.,” said Levine, who is also an environmental epidemiologist and public health physician at Hebrew University of Jerusalem. “It’s manifested in a biological measurement, which is remarkable. It’s not a soft measurement; it’s something that you can count very accurately.” 

Levine said his 2022 study, a systematic review of 223 studies, found a 50 percent decline in both sperm concentration and total sperm count between 1973 and 2018 across North America, Europe and Australia. 

But a more recent study, “Sperm concentration remains stable among fertile American men” published in January, found no clinically significant decline in sperm concentration among American men between 1970 and 2018. 

“We expected to find a subtle decrease over time, not a drastic decrease,” Dr. Scott Lundy, the study’s lead author and Urology Program Director at Cleveland Clinic, said in a blog post. “I think finding nothing at all was a little bit surprising, and it certainly does not mean that we can ignore this issue or not study this further. But in this case, I think there’s at least some evidence to suggest that we can be somewhat reassured.”

Without speaking to any specific studies, Levine said that different methodologies could yield contradictory results. In a meta-analysis, he emphasized the importance of comparing only studies with similar laboratory methods. 

“It’s good that in science there are others who make other claims and try to look at other things,” Levine said. “But when I looked at the literature, I was not convinced that there is no decline. I plan to update our study; maybe there is new data. And I hope that I will find that the decline stopped or even reversed.” 

Levine said recent studies show that a lower sperm count is associated with higher morbidity — meaning a low sperm count can be a marker of poor health in general. He said more research needs to be done to identify the cause of declining sperm counts, but research on animals has shown that certain chemicals disrupt the endocrine system. Obesity, lack of physical activity, smoking, binge drinking, certain drugs, occupational exposures and climate change, specifically rising temperatures, also likely impact sperm health. Levine said his research findings are a clear sign that something is wrong with men’s health on a global level. 

But how much does a declining sperm count impact the falling birth rate in the United States? Levine said it’s not clear, but he suspects that social factors play a bigger role. 

“We know that, for example, women’s education is very related to the number of children in a family,” Levine said. “So I would assume that social demographic changes are the main reason for the shifting trends in fertility, meaning the number of children per woman of childbearing age in the United States and in many other countries.” 

Dr. Michael Eisenberg, a professor of urology at Stanford University, said reports of declining sperm counts have been circulated in urologist circles for decades. While more controversial in the 1990s and 2000s, Eisenberg said there’s been increasing evidence from larger and more comprehensive papers published in recent years. 

“There is still some controversy in the field, but I think generally the consensus is — and I certainly believe — that sperm counts are declining,” Eisenberg said. 

Most of the studies on sperm count are meta-analyses, which are studies of studies. There is no systematic tracking of sperm count or national effort to monitor semen health in the United States. 

“When people think about fertility, I think that unfortunately the male role in that is somewhat undervalued and underappreciated,” Eisenberg said. “I think bringing a lot more attention to it is important. Women have regular cycles, so they have some sense of their fertility potential, whereas men don’t have that feedback.” 

Administration messaging

It’s not the first time that Kennedy has talked about sperm count. In December, he mentioned it during a HHS announcement about coverage for in vitro fertilization (IVF). In April 2025 he made similar remarks to Fox News’ Jesse Watters, asserting that “an American teenager today has less testosterone than a 68-year old American man.” 

Kennedy’s language echoes messaging from Trump himself; Trump has called himself the “fertilization president” and the “father of IVF.” At the maternal health care event Monday, he referred to himself as the “father of fertility.” Other members of the administration have also expressed concerns about fertility.

“Let me speak a little bit about the reality that 1 in 3 Americans are under-babied,” Dr. Mehmet Oz, head of the Centers for Medicare and Medicaid Services, said at the Monday White House event  “What does under-babied mean? That means that you either don’t have any children or you have less children than you would normally want to have.”

The administration has long courted adherents to pronatalism, or the belief that a declining birth rate is the primary problem of our times — and that everyone should do their part to reverse course by having as many children as possible. (Sometime Trump ally and former head of the so-called Department of Government Efficiency, or DOGE, Elon Musk, is an avowed pronatalist and is believed to have fathered at least 13 children by at least four different women.) 

And baked into pronatalism are traditional gender roles and an insistence that women’s ultimate work is having babies.

Kennedy’s comments draw a direct connection between paying attention to the sexual function of men with the need of women to birth babies.

What women want

Karen Guzzo, PhD, is a professor of sociology and the director of the Carolina Population Center at the University of North Carolina; she’s an expert on fertility preferences and fertility behaviors. 

Guzzo said that Kennedy’s comments reflect an insistence on finding a physiological reason for population decline, despite there being no evidence for that. 

The reality is that most Americans who want to have children want to have two or three children. 

“The reason that people aren’t having kids or are delaying having kids isn’t because they’re physically unable. It’s because they don’t feel like they’re able to have kids at that point in their life, given their social and economic circumstances,” she said.

Any increase in infertility is largely due to more people delaying having children. 

“People aren’t just deciding at 18, ‘Oh I don’t even want to have kids until I’m 38.’ It’s usually because they want to get to a point in their life where they’re like, ‘All right — now I have enough money. Now I have a stable partnership. Now I feel that I can provide a good life for children,’” she said.

What research has shown, in other words, is that what really delays someone from having children are economic and social conditions. Guzzo said some of the key factors that allow people to feel the necessary security are affordable childcare, strong unions and union jobs, affordable higher education, and accessible healthcare — including maternal and reproductive healthcare. 

The focus on sperm count? A “clear misdirection,” she said. 

“Young women are like, ‘Yeah I’m not asking for the most sensitive guy in the world. I just want a guy that thinks that I should not die in childbirth and that I can also have a job,’” Guzzo said. “Real men are secure enough in their masculinity that they can, in fact, change diapers and stay home with their children and be active parents.”