Weather 
Gen Alpha boys might not feel so “alpha” when they hear the depressing claim about their sperm.
“In 1970, men had twice the sperm count as our teenagers do today,” Health and Human Services Secretary Robert F. Kennedy Jr. declared on Monday while joining President Trump at a maternal healthcare event in the Oval Office.
This isn’t the first time Kennedy, 72, has made claims about male fertility. He told Fox News’ Jesse Watters a year ago that, “A teenager today, an American teenager, has less testosterone than a 68-year-old man. Sperm counts are down 50%.”
The theory that there’s been a worldwide decline in sperm counts over the last 50 years has been the subject of great debate in the medical community.
Kennedy adds a new wrinkle by bringing teenagers into the discussion, as semen analysis is rarely conducted on minors, so data and research on this group are limited.
Sperm count is an important biomarker because it indicates male fertility potential and serves as a sign of general health. The Trump administration has blamed falling sperm counts and testosterone levels for the US’ declining fertility rate. Here’s what experts have to say about Kennedy’s latest sperm claim.
Are sperm counts really declining?
As you might imagine, this is a difficult thing to measure, especially over time.
Decades ago, scientists used hemocytometers to manually count sperm cells. Flow cytometry, a laser-based technique, is now used to assess sperm concentration and quality.
Dr. Lauren Bishop of Columbia University Fertility Center noted that sperm concentrations can vary by specimen. Sperm concentration is the number of sperm per milliliter of fluid. When you multiply the concentration by the volume of the specimen, you get the total number of sperm for the sample.
“Recent illnesses, such as a cold or flu, can impact the concentration, [as can] the number of days of abstinence prior to the time of collection,” she told The Post.
Perhaps that’s why sperm count studies have offered mixed results.
A 2017 scientific review published in Human Reproduction Update reported a “significant decline in sperm counts” between 1973 and 2011.
This decrease was “driven by a 50–60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand.”
“Unselected by fertility” describes young participants whose fertility status was not known versus “fertile” men in the research, who were known to have conceived a pregnancy. The review was based on 185 studies involving 42,935 men.
Dr. Boback Berookhim, a urologist at Northwell’s Lenox Hill Hospital, pointed out that a lot of the data used for these types of studies comes from men who undergo sperm analysis because they are struggling to conceive.
“These men may have lower sperm counts in general,” he told The Post.
The team of international researchers who conducted the 2017 review published a follow-up study in 2022, finding that sperm concentration “declined appreciably” between 1973 and 2018.
“Data suggest that this world-wide decline is continuing in the 21st century at an accelerated pace,” the authors wrote in Human Reproduction Update. An HHS rep told The Post that this research informed Kennedy’s Monday statement.
Notably, research published last year in the journal Fertility and Sterility found “no clinically significant decline in sperm concentration among confirmed fertile men and the general male US population without known infertility.” The review looked at data collected from 1970 to 2023.
How do teen sperm counts compare to adult counts?
Sperm count comparisons become even more complicated when teens are involved because their sperm is not often analyzed.
A 2019 review evaluated data from 95 adults and 197 adolescents, 11 to 19 years old, who underwent semen analysis in the US and UK for fertility preservation ahead of cancer treatment.
The research found that the adolescents had a median total motile sperm count of 11 million compared to 29 million for adults.
Now, this doesn’t speak to sperm counts in the 1970s, and the median age for the adult participants was just under 31 years old.
Sperm count and quality generally peak in a man’s 20s to early 30s before gradually declining around the age of 35 and especially after 40.
Overall, men younger than 40 generally have higher sperm counts than older men.
So what is considered a low count? Berookhim said it’s less than 20 million sperm per milliliter of ejaculate or less than 10 million motile sperm in the entire ejaculate. Conception could be difficult.
Bishop said there are concerns when the sperm concentration is less than 16 million per milliliter and fewer than 42% of sperm are moving well.
What’s to blame for low sperm counts?
When highlighting male fertility struggles, scientists have pointed the finger at everything from obesity and sedentary lifestyles to toxins like endocrine-disrupting chemicals and air pollution.
“These factors may influence sperm production through hormonal disruption, oxidative stress, mitochondrial dysfunction, impaired testosterone signaling, inflammation or sperm DNA damage,” Ronit Menashe and Vida Delrahim, founders of the prenatal supplement brand WeNatal, told The Post.
Unfortunately, there’s no singular scapegoat for sperm problems.
“We know that smoking and stress affect sperm production. Obesity has a potential effect on testosterone production and in some men is associated with lower sperm production,” Berookhim said.
“The role of chemicals and plastics in general remains unclear, although certain chemicals have a clear relationship wiht lower sperm counts.”
Dr. Ashley Wiltshire of Columbia University Fertility Center said that obesity, smoking and certain chemical exposures can negatively affect male and female fertility.
“Stress/poor sleep may have potential to impact fertility, though the degree of this is not as clear as the aforementioned factors,” Wiltshire told The Post. “Plastics are definitely a concern that we are actively learning more about.”
