Plain English with Derek Thompson - Sperm Counts Are Falling All Over the World—Why?

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So I was on Twitter the other day where it seems like the only thing people talk about anymore are Elon Musk and Twitter and I came across a study that really blew me away.


It was an analysis, A meta-analysis actually of male sperm counts in the last 50 years it said average sperm counts have fallen by 50% and this isn’t something that’s just happening in the US or Europe or Asia.


It seems to be happening all over the world.


In fact, if the current rate of decline continued, these researchers concluded, the, average male sperm count would fall so low, that the typical guy in every Advanced economy would be considered infertile by the year. 2050, that is a child born this year would by the age of 28 live in a world where the average man is technically infertile Now that seemed at the very least pretty damn interesting, pretty damn concerning and frankly kind of under discussed in certain circles.


May be declining sperm Cloud stirred talked about a lot in your other favorite podcast, favorite YouTube person.

But I think about it like the policy level if this country had a national discussion about lead poisoning, we had a national discussion about clean air clean water.



But if environmental factors are slowly decimating, the human populations ability to procreate, that does seem like something policymakers, should talk about more.

So, I started reading about this subject.

And as I learned very quickly, this is a place with unbelievably high, amounts of controversy, there are some researchers who have major issues with this analysis and the scientists behind it.


There’s some people who think this issue is vastly.

Underrated as in people aren’t talking about this enough and there’s other people who think it’s vastly overrated.

People are talking about it and it’s fundamentally Much Ado About Nothing.

But in all these articles that I read a researcher whose perspective, I really enjoyed throughout all of.


It was a Harvard Professor Jorge, Chamorro He is a professor of nutrition and epidemiology.

He knows the sperm count meta-analysis team but he also researches diet, and male and female fertility.

And Professor Charo is today’s guest, in this episode, we break down the data on declining sperm counts.


We tell you what it means.

What might be causing it.

What men can reasonably do to avoid it, how bad it could get.

And finally, we fold this story of declining.

I’m counts into the broader story of declining fertility in the Western World, which is fundamentally a story of not just biology, but also of society and the choices that we make as people, I’m Derrick Thompson.


This is plain English.


Professor shavar.

Oh, welcome to the podcast.

Thank you for having me.

I want to start with this new meta-analysis.

That I described in the open.

Do you know, these researchers and can we trust these numbers?

Yes, and yes.


So I know the the author’s very well.

I’ve collaborated with them.

We freaking papers together.

Are we freaking research proposals together?

And looking at the author least I’ve I’ve written at least one paper we have about half of them on different aspects of male fertility.


So the the research community on male Factor, infertility is relatively small.

So we there’s a really good chance that we all know each other and these are very Senior People, very serious people and that that can be trusted In giving unbiased professional opinion on the work they do.


So I trust them in general and I think as it relates to this paper in particular, its it really is the fourth iteration of trying to get at the same question, right?

Especially from the senior author dr.


Shawna Swan she’s been involved in in four papers during the early 1990s to try to address this question.

Is there a downward Trend in semen Quality.

And each progressively duration, including these one addresses, some of the limitations of the previous iteration and gets closer to a good answer to that question.


So let’s talk about the most important finding of this meta-analysis and you can draw back from that.

And tell me what the most important fact in this field is what should we know, is that the decline and sperm quality a decline in sperm reduction, What is your headline here?



So I think that the headline is that over the course of the time period covered by demand analysis.

So roughly from the 1980s to 2020.

So over a 40-year period or so, the sperm count.

So, sperm concentration total sperm count have calmed down, have reduced by about hats worldwide, right?


And this is, after taking into account, some issues that were in addressing previous version, so, Of these studies, including, is this only happening in rich countries, right?

This is only happening in North America and Australia.

New Zealand and Western Europe.


So these new meta analysis includes data from South America, and Central America from Africa, and from Asia, and it appears that.

The same thing is happening worldwide, the seed have to do with the type of people who end up giving a semen sample.


A research and therefore there’s data that eventually gets published on semen quality and that is addressed.

That was a bigger problem.

The first version of the paper and it’s much it is absolutely a non-issue in this version of the paper and then what was probably the biggest criticism in.


In the 1990s version, the 1992 version of these paper and then the 2400 paper is our is what you’re seeing differences in.

What’s happening at the lab, right?

So the the there really wasn’t a consensus on how is it that you should analyze the semen sample until the late 90s and more recently.


There’s there have the, who has established guidelines that are have become pretty much Universal on how you process and how you evaluate a semen sample.

But in the older papers people were using all sorts of different methods for counting sperm.


So, that was a big issue in some of the earlier versions of the paper.

The newest one uses only includes papers in the minute analysis that use the standard who protocol.

So again, it is less of an issue.

That’s really interesting because I did a lot of reading about this subject and last few days and it seems like there’s been a controversy in the last few years.


Some people think that this issue is being catastrophize that it’s not nearly as bad as the meta analysis suggests and you’re saying that in previous years.

Or even previous decades, people said this is self-selection bias.

People are only turning in sperm samples.

If they have reason to believe that they might have less sperm concentration, or if they’re having some difficulty with fertility, maybe it’s self-selection bias, maybe, it’s mostly phenomenon of lab analysis, but you say this meta-analysis we should act.


We should trust because it resolves or directly answers this.

A lot of these criticisms that have been levied against the this kind of research is that basically right before I move forward that’s that’s basically it.

All right, so I think I think with each different version of the paper or last 30 years or so these group has gotten closer to answering the question.


Is there a downward Trend in sperm counts, right?

And I think these most recent version of the paper gets as get gives us the best possible answer to date which is probably, yes, it probably is the sperm counts.

Are going down and tell me about when this declined happen because you’re looking at a difference between the Seventies early 1980s.


You said there was a meta-analysis published in 1990.

Now we’ve got an update published in 2020.

When did this decline happen and is it a client?

Is it a kind that’s over or our sperm counts continuing to fall in these populations?


So, when is it happening?

I guess.

It depends on how much do you want to really believe previous versions of the meta-analysis, right.

So if you think that, if you’re willing to say, okay, Okay.

Maybe the the methodological problems that were present in the 1992 version of the paper are not that big of a deal and we can use that as a guiding as an initial guide of how long has this been going on that paper included papers from the late, 1930s?


So you could say, like in the in the worst case scenario, the the answer is it may be have been happening since the late 1930s.

The way through today to the 2010’s 22 2010.

The last paper published in the that’s including the meta-analysis in 2019.


So it’s probably 2010’s if you want to be more stringent as to what what is the type of data that we should be allowing to be included in this type of analysis?

Then you would say well it’s probably something that’s been happening from the 1970s forward, right?


So definitely At some point in the second half of the, of the 20th century, maybe a little later, I’m sorry, maybe a little earlier and definitely still happening today.

Now, the question is Is it like you said, is it, is it going to continue to happen?


And we don’t know.

And it really in my mind, it really depends on y, right?

So yes, it’s going down.

But why is it going down?

I’m easy.

It is, is it going down?

Because of whatever is explaining this downward trend has saturated the possible effect that it can have on a population level and semen quality or is it something that can continue to impact Sperm concentration and sperm count that a population level.


And that, that question is not being cannot be answered today, because we do not have a very good understanding of what is causing this downward Trend.

We’re going to get to you’re dealing with grappling with the why question which is you said is is not something we have a firm answer on.


But I think a question that might help to focus us on the why is the where, right?

If every Population around the world was having the exact same rate of decline.

Well, then we would have one set of answers, but if different countries are experiencing different rates of decline that presents a different set of answers.


So, tell me is every region that’s being studied, seeing the same rate of decline when it comes to sperm counts or are some countries in some regions, declining faster than others.

That is for, that particular question, the the current meta analysis, the one that was just published, she’s the one that provides the As possible answer.


So obviously there’s not, there are no studies from every single country in the world included in this meta-analysis it includes data from about 50, Something Country.

So it’s a pretty reasonable number of countries including the study in the meta-analysis 53 countries and eating it.


So the way they try to deal with these Regional variation or is the same thing happening across the world, Is they divide their their samples there.

An article samples between west high-income countries essentially so North America, Western Europe, Australia and Asia.


And then everywhere else in the world, right?

We should there’s there’s fewer studies in everywhere else in the world.

But there’s enough to make estimates of what’s happening outside of Western Europe, North America.

Australia, New Zealand.

And even though there’s a decline in sperm concentration, and total sperm count all over the world.


They decline appears to be less steep outside of North America Western, Europe and australasia.

I’m sorry, Australia.

New Zealand.

So yeah.


So so that part appears to be slightly different.

It’s still, it’s still downward Trend.

It’s just not as severe.

And as just a really quick question, is there a particular country where we see sperm counts are declining?

The fastest like, is it, is it faster in the u.s. than in Europe?


You said that it’s it tends to be richer higher-income seems to me countries that are seeing the steepest decline, is there someplace?

That is just singing the steepest decline the so.

So that is not specifically addressed in these meta analyses of country specific estimates.


But a lot of the initial interest had to We trends that were identified in northern Europe, mostly in Scandinavia, which coincidentally is where some of these were some of the investigators are based.


But, and then the question was a wall to, is this only a Scandinavian thing or is this something happening more generally and that’s how most of these research evolved and and has continued to evolve and it does appear that, it’s a more generalized phenomenon and then they should Is why?


And is there a bottom, right?

So is are we racing 20?

Or is it going to stabilize somewhere above zero and and that’s exactly how I want to structure the rest of the conversation.

I want to talk about, why?

And then I want us to talk about how bad is it?

And how bad could it get?


So you’ve already said that, the why here is is complicated and we don’t have a crystal clear answer as to what is causing sperm counts to decline especially in some of these Western countries.

Give me some of the nominees.


What are some of the more popular explanations for why this is happening?

So so when you, I think there’s always a little bit of discipline by, as when you try to look for answers as to why something’s happening.

And I think what has happened with the semen quality decline, is a really good example of that.


So there’s the a lot of the investigators involved in these particular study and more.


A lot of the people who do research on human fertility, come from an environmental health back room for historical reasons.


And so if you look through the literature as, like, why is this happening?

The what, what people have always tried to do is look for answers in some not entirely specified Environmental.


Right, so maybe eats chemicals, entering into the world Supply, maybe it’s our pollution, maybe it’s right.

So so there has been, what has been clear from that research, is that there is not anyone environmental factor, that is explaining these overall downward Trend.


So it is, it is possibly true that there are a variety of adverse environmental exposures from environmental chemicals that get that enter.

Broadly into exposure in human populations through to air pollution or other factors that are associated with that.


Contributed a little bit to this decline, but I don’t think that’s the entire story.

Most of my research has to do with nutrition and lifestyle factors as they relate to fertility.

So I tend to approach this problem from a different perspective.

So, for when I see these data, the one thing that could catches, my eye is that the downward trend has coincided more or less with rates of obesity.


Is white.

And so and we know from from Individual from from other studies.

Not necessarily trying to look at the downward Trend by trying to look at what might be the impact of nutritional factors and malefactor fertility.

That BMI is a really, really strong predictor of semen.


Quality of sperm concentration, right?

Especially at really high levels of obesity.

It is known to decrease sperm counts quite substantially.

So it is Is quite possible that worldwide changes in the frequency of obesity are also contributing to these and other things that have happened at the same time.


That obesity rates have gone up, is that diet how people eat across the world has changed quite dramatically.


So, the, the amount of food that we eat, that is prepared outside of Home, has changed quite dramatically the amount of sugary beverages that we drink has changed quite dramatically and all over the world and each one of these factors Has been associated in every nephew studies with lower sperm concentration.


So I think that that we will never find V1 answer of.

Why is it that sperm counts are going down?

Because there is not a one answer, it will be one of these things where there is, it’s a many little, a wide variety of small problems.


We when you Put them all together way down testicular function and is manifested as lower sperm comes.

I want to offer what I take as a kind of synthesis of that answer.

And then throw it back to you to let you tell me if I’m understanding this, right?

It seems like you’re saying, we should have two groups here.


Group number one are the ecologist the environmental researchers.

They’re looking at, what’s happening in the outside world that might be affecting.

Our hormones are endocrine system and they’re saying it might be all of these man-made products.

Plastics in the creams and the cosmetics in the cleaning products in the drugs that were putting into our system or coming into contact with and they’re messing with our hormones, they’re messing with our bodies in such a way that it’s having some kind of hard to disentangle process that is cashing out as a steadily.


Declining sperm count as if it’s and it’s a dosage affect, the more we interact with these substances, the more our sperm counts continue to decline over time.


You’re saying there’s another explanation which is that it’s not so much about this sort of the, the, the chemicals it’s about obesity.


That obesity itself is having this direct relationship to sperm count.

Is it possible that both groups are right, that?

What’s happening is they’re actually telling the same story that there are chemicals in our foods that are making us obese and those same chemicals.


Are having a secondary effect on our hormonal system, that’s having this other outcome of declining sperm count.

So yes, obesity might be directly causing the declining sperm count.

But also there’s the chemicals in our foods that are making us a base or having this secondary effect of reducing, our sperm count is something like that possible.


Yeah, I guess I wasn’t entirely clear on my previous time on the microphone, but I think that’s exactly what I meant.

Is that environmental contamination is not the only thing that that’s that’s the answer.


It is, it’s not the only answered as to why this is happening, but I would, I would phrase I would frame it slightly differently than you did, right?

Which is you’re saying environmental chemicals.

Some of those are obesogenic and obesity in sap directly affecting spermatogenesis and these and these Our mental chemicals Also may have a direct effect on spermatogenesis independently of obesity.


I think that does happen but there’s all but at the same time there are there are many causes of obesity that are independent of obesogenic chemicals.

And many lifestyle factors that have an impact on self-promoter, Genesis independently of obesity, right?


So I think that there’s what I wanted to say, I guess, is that there is no one.

Cause right.

There’s not there’s not going to be one lever that you’re going to pull and you’re going to say we’re done, right?

There’s probably hundreds of them.


You made that point very clear.

I did not want to suggest that you didn’t make that point.

Clear that there’s definitely multiple causes here.

I yeah, I and you did a great job of summarizing my my hypothesis.

Is there a possibility that it’s the chemicals are having this forking effect on one fork they’re causing obesity and another Fork they’re causing a decline in sperm count.


You’re saying maybe that’s one of many things that’s happening but the most Thing is that it’s just a wide portfolio of effects that we think are causing this as you know, as someone who’s concerned about this.

If I’m, if I’m listening to you and say, all right, there’s a scientist that’s telling me that there are many different features of the modern world that might be two claws.


That might be causing declining sperm count.

It’s, it’s the, the products that we buy and we come into contact to, and it’s also the food and drink that we’re putting into our bodies, you know, I can’t realistically.

Akley, but I like face creams.

I like putting on face creams.


I like buying soaps at CVS and shampoo at CVS that might have some of these substances.

I use Plastics like, every other normal person, I’m not going to stop doing these things.

If you had to sort of rank order from me, the, the causes that you have the most confidence in that are causing this decline in sperm count, you know, with the understanding that this is unsettled science.


What do you think we have the most confidence is a driver of this phenomenon?

So I think and again, my ranking will be different from may be different, from the ranking of some of my colleagues that I work with closely.

But I think if I were to weigh it, in terms of quantity of evidence, I would say that probably excess body weight is the biggest one and in terms of having an impact on on sperm count, And that one’s a little tricky though.


Because why are things that we’ve seen?

Is that yes.

Definitely men with obesity, especially men with severe.

Obesity have significantly lower sperm counts.

Then the question is does losing waiting proof, sperm counts and the literature and that is actually quite confusing.


So probably the best thing that you can do is Stop.

It is modified your life in a way that prevents you from gaining weight and it in the first place, right?


Fortunately, in a way most of the people who are interested in these are relatively young, right?


And therefore still have a lot of potential Gate Weight to gain in the future.

So, just preventing that additional weight from being gained is, is it may be the most important thing, they Can do to protect their testicular function.


I want to talk about how bad this news is and what it means.

So I read in the course of my research for this, that average sperm count has dropped more than 50% in the last few decades, but it seems to still be on average in the normal range, which means that it could still fall further and it could get into abnormal ranges.


But overall it seems to be in In in the normal range.

So if sperm counts are still within the normal range.

What is the most significant implication would you say of declining sperm count?


Okay, so I think there’s two two important implications when one is what do declining sperm counts?

Tell us about men’s fertility potential.

What does it tell us about their future potential to Father a pregnancy when they want to Father pregnancy.


That’s number one and one that and that’s probably the one that gets the most attention.

And the second one that’s probably often overlooked is what does this tell us about mens overall film, right?

So So these cells anything about mens future cardiovascular risk or future risk of dying early.


And so let me start with the first, right?

Because that was the one that probably not only the one that the progressives the most attention.

But also probably the one that we have slightly more information to answer.

So the first question is is it going to matter in terms of Affecting fertility and then so the answer is maybe but we’re probably not at a we’re probably not yet the population that these would be a major emergency at a population level, right?


So what do I mean by that?

So what the the two outcomes that they’re looking these meta analysis?

And in part they are because they’re the ones that can be more objectively, ascertained, and replicated across different Labs, right?

Our sperm concentration, and total sperm count.


And we know from studies as far back as the as the late 80s, that sperm concentration specialist from concentrations, from kind of mirrors.

These relationship tool for going to extend, it is related to the probability that that a couple who’s trying to get pregnant will Pregnant, right.


But this relationship is most easy strongest at the lower end of sperm count.

So what do I mean by that?


So the difference between having 1 million sperm per milliliter and having 10 million sperm per ml.


So those two counts would be considered abnormal.

That difference is in Norms in the in the in the in the in terms of the probability of other and a prayer I can see the probability that the the difference between that’s a 10 million sperm per milliliter and 20 million sperm familiar.


Yes, we’re moving in 10 million.

Increments that difference is also enormous, right?

So those 20 million sperm, they’re super super important.

Now, how about the difference between 50 million and 60 million sperm?

So it’s the same ten millions for a movie difference.


That difference is a lot less important.

So what No.

Is that within the first 50 million sperm perimeter or so, for total sperm count, and if any gain is makes a huge difference, in terms of the probability of getting pregnant, from the range from about 50 to 100 million, it makes a difference, but it’s not that important.


And once you get past 100 million per mail, it makes essentially no difference.

If you have 100 million or 150 million or 200, Ian sperm per Mill, it doesn’t change at all.

Your probability of failure, and a pregnancy and just to quickly to ground us.


What is median?


What is normal?

So so it is, it used to be and if you look at the results of meta-analysis, that the, the the automatic response would be well somewhere around 100 million purpose, America sperm per mil, right?


That would be kind of your automatic response.

Like, Your average guy on the street, without any problems should have around 100 million.

What we’re seeing is that at that?

That’s actually no longer the case it’s more.

It’s closer now to 50 to 60 million, like your average guy on the street probably has 50s, and 60 million sperm per mil count.


So, it now appears that the average guy in the street, is getting close to the range where it might start making a difference too.

In the probability of getting of fathering a pregnancy, if they are trying to get pregnant.


Now the question is how much lower can you get to start making a difference on how big a difference is that going to be, right?

So, is that going to be a difference?

Like, if you look at couples who are trying to get pregnant on their own and they do not have any known fertility problems, any history of infertility, anything like that, the average couple steaks two to three menstrual cycles to get pregnant.



That’s that’s your average couple and and then from then on ders, there’s couples take slightly longer slightly longer slightly longer.

So what is it going to be?

The difference?

Is it going to be the difference between taking two to three menstrual cycles and taking through 24, right?

So that’s a shift of one month and but probably not a big deal for most couples.


Or is it going to be a difference between taking two to three menstrual cycles and taking seven to eight menstrual cycles, right?

So still technically not infertility.

But that might start getting a lot of people more concerned, especially ones you layer on top of that worldwide Trends in when and how people decide to reproduce, right?


So in general people are deciding to have fewer children to have children at later ages.

So once you start layering these things on top maybe a difference of let’s say three or four months in median.

Time to pregnancy is a big deal and and the problems that we really do not have a good answer to what are different ility implications of these.



So yes, there’s more men who are now in the range where these may be a concern, but we don’t know what is exactly the concern and how concerned should be.

I really appreciate that breakdown, and now I’m going to do something that’s a little bit dangerous, and a try to express a piece of Statistics, even though I’ve never taken a class in statistics, so you tell me how catastrophically wrong I am here.


Even as the average sperm count seems to be generally in a normal range.

The lower the average gets given, the fact that there is going to be across the male population, a distribution of sperm, It’s the lower, the average gets the more we should expect people men to be below average, right?


So it could be the case that the average is being brought down.

Not because say half the population is getting more infertile.

But rather because something like 5% of men for whatever reason are seeing significant significant declines in sperm count, while the rest of men are not necessarily singing that same.


Debbie can’t Decline.

And so this makes me think are we seeing this effect like across the population relatively evenly, or these declines being driven by a subset of the population?

Yeah, that’s actually a great question and and that is a question that I wish they had addressed in this paper.


So maybe that’ll be the 20:27 paper or something like that.

So and I think it has to do with the way in which they collected data, right?

So they were collecting averages and they were collecting average measures per year from each of the studies that contribute data to study.


What I think would have been very interesting to see is well, for example, what is the proportion of men within each study?

We at each year, right?

That have sperm concentration or throw sperm count that is below the who caught of reference value for for triggering an evaluation for fertility in the context of of an infertility couple concerned about their fertility and we do not have that data.


I agree with you that you would expect that the proportion of people falling below.

Low value thresholds would be increasing as the mean is decreasing.

So two things that would be definitely true if you always had a normal distribution.


But we know that semen quality, especially especially these two parameters, sperm concentration and total count.

Do not follow a normal distribution, so we do not know to what extent that movement of the mean is affecting the bottom tail of the distribution and that would have been extremely Extremely useful information to have that unfortunately do not have thank you for that and I’m glad that we did we got into a bit of the a bit of the weeds there.


Let me I have to make sure that I’m especially your time.

We have couple minutes left.

Let me let me let me ask the next question.

This way, I’m interested to know whether you think even if this is not a population-wide crisis, now it will be a problem in the future.


So if sperm counts continue to fall, About 1% a year at what point according to your expertise?

Do we get into the danger zone?

Let’s just let’s just assume like it continues to fall at the same rate every single year.


Is there a year a decade?

We’re looking out.

You say, all right?

That is the sperm count number, that would start to get me concerned.

Okay, so again, I don’t have a crystal ball so I hesitate to prognosticate But I’m going to try to to, to humor you on on your question.


So I think that if we start to get populations where they mean is like closer to 20 million sperm per mil, right?

That that two versions of the usual manual for semen analysis, 20 million per Mill.


Was considered male Factor, infertility.

Like so if on average an entire population, has that Nova Certain con that will probably very concerning.

So that would that I would expect that you would see a lot more infertility.


That is not explained by delay.

Childbearing, that is not explained by our new things and just that is explained just by those sperm concentration in a population.

So, but but then there’s several caveats to that one is will if it is it the case that we’re going to continue to have a decline in sperm concentration.


Of approximately one percent per year.


And probably not my guess.

Is that at some point we’re going to we’re going to heat a a plateau right?

Where I don’t know.

There might be a plateau and it maybe that will stop.


And so that’s one thing and in terms of of concerns that I think we’re probably going to be seeing concerns on The long-term health of these men, probably before we see concerns on the fertility of populations as a whole.


And what I mean by that is that there’s there’s some very interesting emerging evidence suggesting that lower sperm count and other markers of lower testicular function.

Like Lord testosterone levels, right are actually Associated.

Not only directs are associated with risk of Of major chronic diseases, right?


Their entry and and and also with an specific Health outcomes, like the risk of being hospitalized for whatever reason, more diabetes, more heart disease, and more premature mortality.

So the literature on that is still is still emerging.


So, for example, so one of the things that is, well, if you have a low sperm count or less likely to have children to what extent these health effects that you’re seeing are Cause your social structure, 20 years down, the line looks very different and looks a lot less supportive than the social structure of somebody who had children.


So whether it is because of underlying common biological Pathways that led you to die earlier or where it is because you end up having Downstream consequences.

Like you have a very different social structure because you have fewer children and therefore a much smaller social network, 20 years down the line, we don’t know, those are things that we still need to know.



But I’m actually more concerned about that part of the population health impact on the fertility health impact, it’s actually make sure.

I understand you, you’re saying that declining sperm counts might be sort of like a canary in the coal mine when it comes to health.


It’s not that decline it that the lower sperm counts themselves are bad for someone’s Health, but rather that the factors that cause sperm count, declines, might suggest that lots of other things might be going wrong that are bad for health.




So so I mean you can think of the time I like to think of the testes as really two organs that happen to share a common anatomical site, right?

So there’s there’s an endocrine organ, that’s in charge of production of testosterone and estradiol and other hormones, and there’s and there’s the reproductive hormone organ, which is in charge of making sperm, right?


So you can have, you can have things that affect one part, but not the other, you can have things that affect both and the, the effects on the endocrine.

East is right on the on the hormone making part of the testes.

We know that that hormone production testosterone production is associated with out wide variety of other health effects, right?


So especially as it relates to cardiovascular health as Men, start to age.

So my concern is that what we’re seeing with sperm counts is actually a global effect on sperm function in general.

That will end up having long-term Health consequences.


When says on cardiovascular disease, premature mortality diabetes.

Before we start seeing the fertility effects in younger cohorts of men and we are we it does?

We and we haven’t had time to get into this, but we are simultaneously seeing declines in average testosterone levels as well.


And so we’re seeing this, we’re seeing this decline in both of these functions.

It’s interesting.

I wanted to end on the concept of fertility because We waved at this point, but I think it’s really important to go at it.

Head on, you know, there are a lot of interpretations of declining, sperm counts to say.


Okay, this is our explanation for why fertility is declining around the world, it’s because of declining sperm counts.

But you’ve done a really good job in your research and in other places that I’ve watched explaining that there are a lot of other social factors that contribute to the decline of fertility, especially in higher income, Western Is what do you consider the most important drivers of lowered children per couple in these Richard societies, right?


So so I think it’s important to try to Define what is there were talking about, right?

So when you, when you say fertility, you kind of get an idea what you’re talking about, but you do not always, you’re not always talking about the exact same thing, right?

So there’s like the demography definition of fertility.


Which has to do with how we how many children on average Do women in a population have and is that enough to sustain the population or make it grow?

Or make it shrink, right?

That’s that’s one concept of fertility.

And then there’s there’s a more clinical concept of fertility.


Which is, are you able to have children when you want to have children, right?

And those two things are related, but they’re not the same, right?

So, so one that you have a lot of data worldwide.

Is the first one, is the demographic one, right?

So you can count wiemer reproductive age, you can count babies and it’s really easy.


To say, okay, the on average women in this country, or that country having one point two babies per woman.

So, that would be something like, South Korea, or Japan, which is very, very low or Spain.

Or then you go and say, well, this country has on our has a little closer to 2, which is a little north of Twitter replacement levels of United States is around 1.7.


So we’re below replacement and you go to some parts of Asia which are growing and you have numbers of in the two or three.

So that’s one concept of one way of thinking about fertility and on when you think of her kill you that way as well as when you’re you’re you have to also think about why are people getting pregnant, right?


So there’s in the, in the post 1960s world.

We made an enormous transition from All of our ancestors, right?

So up through the 1960s, when, when they’re, when all of a sudden, we introduced to our species effective contraception with the introduction of oral contraceptives.


We now can as a species decide we want to have children.

Yes, or no.

And if we want to have children, when do we want to have children?

So what you’ve seen is that on average, people are deciding to have fewer children and people You are deciding to have children later in life, why?


Because it makes sense, it makes sense.

That if you do not have to worry about finding a life partner and then enjoying your life and going to school getting a profession and not and do all of that without having to worry about about that.


About the fact that you may get pregnant.

Any one moment that you will not take advantage of those opportunities if you’re a woman.

So women do it.

Unfortunately, what I think is especially in high-income societies is that we we haven’t quite realized that contraception is not a pause button on fertility.


Rite convey.

It it helps you to delay conception, but your reproductive system continues to age.

Even during even while you’re not able to get pregnant because of contraception.

So when you have, for example, places like Massachusetts for did the median age at first birth is around, is around 35, right?


Then you start having entire populations that are trying to get pregnant for the first time.

When we know that you’re having the most serious declines in fertility, as it relates to ovarian reserve.

And we also So know that then you’re having men who are trying to get pregnant.


We’re trying to do to become fathers for the first time the meat too late 30s.

And we also know that men men’s age also has an impact on the chance of getting pregnant.

So I think that as fantastic for economic and professional development as contraception has been, it puts us in this quandary where we have a mismatch between cultural expectations and Economic and for pursuing economic and educational opportunities and reproductive biology.


And we’re going to have to figure it out.

Somehow, it’s a complicated subject when that I should definitely do other podcast about.

But I think that was really exquisitely, well said, and I appreciate that.

You put the issue of sperm counts and fertility in this wider social context because the social context is just so unbelievably important.


In terms of understanding the bottom line number of the Ocean of fertility in this country and in others.

Professor, thank you so much for walking us through the statistics.

The numbers, the cost is the implications I really appreciate it.

Thank you very much.

Thank you so much for having me.


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