As a physician, Democrat, and bear lover, I don’t support anything RFK Jr. stands for.

However, he made headlines last week for talking about the hormonal and reproductive health of American men, and so I had to listen, review, and respond.

RFK Jr. - like Trump and all his cronies - speaks in partial truths. They are all experts at taking a fragment of truth and distorting it into a broad generalization. In the case of RFK Jr., he even manages to do this with historically factual areas like science and medicine.

In his recent interview with Fox News (of course with them), RFK Jr. made statements about men’s testosterone levels, sperm counts, and fertility rates in America (1).

In this article, I want to review each of these statements, fact check their accuracy, and then discuss what RFK Jr. is actually concerned about when he makes these claims.

“A teenager today, an American teenager, has less testosterone than a 68 year old man”

This first quote from RFK Jr. focuses on testosterone levels between male teenagers and 68 year old men.

This is probably his most inaccurate statement of the four we will discuss. There is clear evidence that testosterone levels decrease over time in men. Research demonstrates that total testosterone decreases on average about 1.6% per year, while free and bioavailable testosterone (or rather the testosterone not bound to proteins and so active in a man’s body) falls by between 2% and 3% per year (2). Therefore, unless a 68 year old man is taking testosterone or the teenager has an abnormal hormonal deficiency, there is no truth to levels of testosterone being lower in teenagers compared to older men.

Another aspect to consider when discussing testosterone levels in men is an understanding of what are normal levels. A 2017 study of over 9,000 men in the U.S. and Europe established the first harmonized reference ranges for testosterone levels. This study concluded that men between the ages of 19 to 39 have a normal testosterone level if it falls between 264 and 916 ng/dL (3).

This is a large range for normal, and this range can get even larger depending on the time of day testosterone is measured (4). The harmonization study controlled for this fluctuation during the day, but not all studies or data will. Even with accurate data and well-controlled studies, ‘lower’ or ‘higher’ means less than ‘normal’ and ‘abnormal’ when it comes to testosterone levels, and so this nuance should be addressed when discussing hormone level trends.

Conclusion: RFK Jr. is completely wrong when it comes to younger men having lower testosterone levels than older men in America, and he misses the nuance around the range of ‘normal’ values.

“Testosterone levels have dropped 50% from historic levels”

RFK Jr.’s second statement about testosterone is just as bold but a bit more nuanced than his first.

Interestingly, there are two large studies that support the claim that population wide testosterone levels have dropped over time.

The first study looked at 4,045 men from the National Health and Nutritional Examination Surveys (NHANES), which are surveys collecting medical information conducted by the Centers for Disease Control (CDC) in the U.S (5). The study looked at men within the following age groups: 15 to 19 years, 20 to 29 years, and 30 to 30 years. They compared testosterone levels in these age groups from 1999 to 2016 and found that all age groups had statistically significant decreases in testosterone. This is shown in the paper’s figure:

It is known that the increased body mass index (BMI) associated with being overweight or obese decreases testosterone levels in men. Given that the obesity epidemic in the American population continued to increase over this time period, this testosterone trend could be attributed to the increase in weight. However, when the authors corrected for BMI, the trend for decreasing testosterone in these age groups persisted, meaning that it is not the only contributing factor to testosterone decline in the population.

The second study to look at population-wide testosterone levels over time comes from the Massachusetts Male Aging Study (6). This study was composed of randomly selected men between the ages of 45 and 79 living in the Boston area. Testosterone samples were measured between 1987 and 1989, 1995 and 1997, and 2002 to 2004 from a total of 1,532 men.

The study demonstrated that population-level decline is greater than the decline typically associated with age, meaning that testosterone levels were dropping faster than expected. These conclusions remained even after adjusting for variables such as weight, medications, and smoking, and the authors stated that a 65-year-old man in 2002 would have testosterone levels 15% lower than those of a 65-year-old in 1987.

Conclusion: RFK Jr. is right that testosterone levels are decreasing on a population level, but the decrease is closer to 15% rather than 50%.

“Sperm counts are down 50%”

RFK Jr. then shifted from talking about testosterone to talking about sperm, as you do.

There are a number of factors that can affect sperm counts, including age, surgical history, genetic problems, systemic diseases, medications, and environmental toxins (7). Some of the common offending agents from the environment include pesticides, cigarette smoking, and excess alcohol. Some of the most common medications that decrease sperm counts include marijuana, opioids, and testosterone supplementation.

As a reminder, RFK Jr. has admitted to taking testosterone supplementation himself (8).

In terms of population wide sperm counts, the data suggests that RFK Jr. is surprisingly accurate in his statement. One publication found that the average sperm count in 1940 was 113 million/mL but dropped to 66 million/mL in the 1990s (9). This is in line with my own sperm count, which was 65.6 million/mL prior to making embryos.

Another publication looked at sperm counts from around the world between 1973 and 2018 and found that the average sperm count declined by 51.6%. Even more concerning, this study found that the rate of decline in sperm counts accelerated after 2000 with the average decrease doubling in the last two decades (10).

Conclusion: RFK Jr. is right and sperm counts are down by about 50%.

“We have fertility rates that are just spiraling”

After sperm, there really is nowhere else for RFK Jr. to go except to talk about fertility.

Infertility affects about 15% of all couples in the U.S. and at least 180 million couples worldwide. The male is solely responsible in about 20% of cases and is a contributing factor in another 30% to 40% of all infertility cases. Overall, the male factor substantially contributes to about 50% of all cases of infertility (11).

The 2025 United Nations World Fertility Report states that in 2024 the average global fertility rate was 2.2 births per woman. This is down from 5 births per woman in the 1960s and 3.3 births per woman in the 1980s (12). This is a drop of over 50% in the last 60 years.

In the U.S. specifically, the decline in birth rate is similarly dramatic from the 1960s to present day:

The fertility rate in the United States reached its lowest level just above 1.6 births per woman in 2023. The replacement rate, or the number of births per woman to prevent a population from declining, is 2.1. The U.S. population has and will continue to increase due to immigration, but it is projected that the country’s birth rate will continue at around 1.6 until 2054 (13).

Conclusion: RFK Jr. is correct and fertility rates have dramatically decreased and are not projected to be at replacement rates in the U.S. for at least the next 30 years.

But Why is RFK Jr. Talking about Testosterone and Sperm?

This seemingly random collection of male health facts comes from RFK Jr.’s campaign to ‘Make America Healthy Again,’ with a specific focus on banning artificial food dyes.

But are artificial food dyes in any way related to decreases in male testosterone levels and/or sperm count?

There are animal studies with albino rats that show artificial food dyes can have an effect on the male reproductive system. However, in these studies, the rats were given doses of the artificial dyes that were 100 to 500 milligram per kilogram (14). With the average human man weighing about 80 kilograms, this would equate to giving a man 4,000 milligrams or 4 kilograms of artificial dye. This is an insanely high amount compared to what is in ultraprocessed foods, but the animal model is meant to show that there is an effect on male reproduction and so there could be an effect of smaller dose over an extended period of time.

As usual, RFK Jr. is missing the forest through the trees. As an endocrinologist, I do not support artificial food dyes, but I am even more against the modern diet of ultraprocessed foods. Recent studies have shown that ultraprocessed foods - or foods with 5 or more ingredients - have been linked to early death (15).

There is no doubt that this type of diet and a more sedentary lifestyle have contributed to innumerable medical and public health consequences over the last 75 years. Even though the previous studies of testosterone levels and sperm count have adjusted or corrected for these as confounding factors, I still believe there is truth in their impact on our overall and reproductive health. A meta analysis, or collection of studies, found that “adherence to a Western dietary pattern, emphasizing higher consumption of high-fat dairy products, processed meats, and lower intake of vegetables, whole grains, and fruit, is adversely correlated with sperm concentration” (16).

What is RFK Jr. Really Talking About

Testosterone, sperm, and artificial food dyes are all tangentially related to RFK Jr.’s (and Trump’s) focus in this area: Pro-natalism.

Trump, who is the self-proclaimed ‘Father of IVF’ (17), and other Republican heavyweights like Elon Musk are very concerned with birth rates. Elon Musk has 14 children, many of whom were born with assisted reproductive technology (18). He has catastrophized that Italy is disappearing (19) and stated that South Korea should ‘make kids, not war’ (20) because both of these countries have elderly populations with declining birth rates.

As the founder of an organization meant to help people have children through IVF and surrogacy, I am very pro-family and pro-children. However, it feels like this is a means for the Republicans and right wing of the American population to overpopulate the country, taking up more resources and making it harder for those who don’t fit their ideology to access them.

It feels weird and wrong, like many of the things Trump and his administration are doing. However, it pains me to admit that RFK Jr. and his statements on male hormones and reproductive status are not completely wrong. Credit where credit is due, but it will be interesting to see where this conversation goes with regard to American (and global) fertility.

References:

RFK Jr. Is Surprisingly Not Completely Wrong About Men’s Testosterone and Fertility

BABYMOON FAMILY

RFK Jr. Is Surprisingly Not Completely Wrong About Men’s Testosterone and Fertility

Our Surrogate Got Pregnant…By Her Husband

BABYMOON FAMILY