Dr. Shanna Swan has invested over 20 years in studying the alarming decline of sperm counts in America.

As an environmental medicine specialist at Mount Sinai Medical Center in New York City, Dr. Swan has produced some of the most pivotal research on this issue. She has also penned books and spoken extensively on the related drop in fertility rates.

Thus, it was a moment of delight for Dr. Swan when she noticed her work being referenced by Health and Human Services Secretary Robert F. Kennedy Jr. shortly after his remarks on October 16.

During a press briefing, RFK Jr. remarked, “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.”

It was unclear if RFK Jr. was drawing a comparison between today’s teenagers and 65-year-olds today, or to 65-year-olds when they themselves were teenagers.

An HHS spokesperson later confirmed to the Daily Mail that RFK Jr.’s statements were inspired by Dr. Swan’s 2017 research paper.

Dr Swan told the Daily Mail: ‘I am glad that sperm decline is getting some attention… and, you know, I am concerned about fertility.

‘I’ve been doing this research since the late 1990s… so, I am happy to see when anybody, particularly people in authority, recognize that this is a problem.’

Dr Shanna Swan, the expert behind the most influential sperm studies, is pictured above at a gala in Los Angeles on October 29, 2014

Dr Swan was the co-author on the  2017 study that first warned of the ‘spermageddon’ crisis that researchers say could upend men’s fertility. 

Analyzing data from 1973 to 2011, the team found that sperm counts had plummeted 52 percent on average during that period, leaving fewer sperm available to fertilize an egg. 

It’s one of the leading culprits behind rising cases of male infertility and researchers blame sedentary lifestyles, higher obesity rates and toxic chemicals.

At the same time, the US total fertility rate has also declined, dropping from 2.52 births per woman in 1970 to 1.62 in 2023, the latest date available, although experts link this to other factors like increased focus on career and concerns over costs.

And other papers have since suggested that sperm counts are not falling by the same magnitude, although they say there also appears to be a modest decline.

The HHS spokesman also cited a separate follow-up 2022 meta-analysis by Dr Swan that led her to warn sperm counts could reach zero, on average, by 2045, forcing couples to seek fertility treatment.

Dr Swan said she was not contacted by HHS for details on her research, although she was pleased to hear it was being cited.

However, she said it was not entirely accurate, based on her work, to say that the sperm counts of teenage boys today are half of those of 65-year-old men alive today.

The researcher said that what RFK Jr likely meant was that teenagers today have 50 percent lower sperm counts, as well as lower testosterone, today than today’s 65-year-olds did when they were teenagers.

Shown above is a stock image of a pregnant woman with her partner

Testosterone and sperm counts are linked. Doctors say that higher levels of the hormone drive the body to produce more sperm.

Dr Swan said: ‘I don’t take issue [with RFK Jr’s comments].

‘Overall… sperm counts have declined by about one percent a year since about 1973, and, if you look more recently, from 2000, then the rate of decline has increased quite a bit.

‘So, what we are seeing is an increasing rate of decline; they’re declining faster in recent years. It looks like testosterone levels are declining too.’ 

Warning over the risks posed by falling sperm counts, she said: ‘A while ago there was a Danish study that looked at chances of conceiving and how long it would take to get pregnant if sperm count was at a certain level.

‘What it showed very dramatically was when sperm got to about 40 million [sperm per milliliter of semen], chances dropped off very fast, down to zero. So, zero sperm, of course, your chance of getting pregnant is zero. 

‘But that chance climbs up, and when it gets to about 75 million [sperm per milliliter of semen], it levels off, and then it’s all good. It doesn’t matter if it’s 75 or 150 million. It does the job.

‘But now, we’re getting closer to that point where it’s definitely taking longer to get pregnant. Not impossible, but taking longer.’

In an interview with The Guardian in 2021, Dr Swan warned that sperm counts may be so low that ‘most couples may have to use assisted reproduction by 2045.’ 

Robert F Kennedy Jr with Donald Trump at the press conference in October, where he warned about the decline in sperm and testosterone levels in men

Symptoms of low testosterone include low sex drive, fatigue, decreased muscle mass, depression, and weak bones, among others

Other researchers, however, have previously raised concerns over Dr Swan’s research, saying that doctors can find it difficult to accurately count sperm in a sample.

Scientists say the factors driving a reduction in sperm counts and testosterone are broadly similar.

Both are affected by poor diets, obesity, environmental hazards like chemicals and a lack of exercise.

One paper published this year by researchers at the Cleveland Clinic and Case Western University suggested sperm counts had dropped by about 0.35 million sperm per milliliter of semen every year globally between 1970 and 2018, when results were adjusted for region and fertility status, in what the researchers called a ‘modest annual decline’.

Unadjusted results from the same paper, however, estimated that sperm counts had remained level in the US between 1970 and 2018.

The researchers behind the study said that they did not believe that even a modest decline was likely to lead to a rise in infertility rates.

The paper suggested that the average sperm count was currently around 78 million sperm per milliliter of semen in the US.

This was well above the threshold where doctors say a man would be considered infertile, at about 15 million sperm per milliliter of semen, and within the World Health Organization’s estimate of a healthy sperm count, between 15 and 250 million sperm per milliliter.

Testosterone levels peak in young adulthood, around age 20, but decline by about one percent annually after age 30. This data is from a University of Wisconsin study 

Estimates suggest about nine percent of men in the US are infertile. For a man to be diagnosed with infertility, it means he has a low sperm count or sperm that is not of sufficient quality.

Globally, estimates suggest that the number of men experiencing infertility has risen 76 percent since the 1990s.

Among women, 13.4 percent are infertile in the US, according to the CDC. Researchers at Johns Hopkins University say this level has remained largely unchanged in recent years. 

Overall, about one in six couples in the US struggle to conceive. 

Dr Jeff Singer, a senior fellow at the Cato Institute in the Department of Health Policy Studies, previously told the Daily Mail: ‘What I can say is that Secretary Kennedy has taken a couple of real studies and turned them into a sensational sound bite.

‘There’s some evidence of modest downward trends across generations, likely tied to lifestyle and health factors, but nothing close to Kennedy’s doomsday framing.

‘His claim badly distorts the data, confusing normal aging with supposed generational collapse.’

America’s fertility rate has been in decline since the early 2000s.

Latest data showed the rate was 54.5 births per 1,000 women aged 15 to 44 years in 2023, a three percent decrease from the previous year. 

The number of babies born in the US declined to 3.6 million births registered in 2023, the latest year available, down two percent from the previous year.

Experts warn that the US is heading for an ‘underpopulation crisis’ by 2050, when too few people are born to support its current economic system.

They say that if birth rates continue at their current rate, the natural-born population of the US could be extinct in just 500 years.