What's the deal with testosterone?

22:05Emily Oster:So your pituitary gland secretes a substance that kind of tells the testes to produce testosterone. If you have a tumor in your pituitary or you had a stroke in a certain place that's preventing that from happening, the testes just won't produce testosterone. They're not getting the message from the brain to do it. Those are the only FDA-approved indications, and less than 1 % of men with low testosterone have one of those indications. So virtually everyone getting testosterone replacement therapy that you hear about is technically getting it off-label, which is fine. It is legal to get drugs off-label.

22:39Emily Oster:But I think it does lead to the question of like, OK, why isn't there an FDA approval for age-related low testosterone, which is just the fact that testosterone slowly goes down when you're aging? Caveat, RFK Jr. has said he wants the FDA to investigate this and maybe there will be an approval in the future. So I think that's where we kind of have to start is like what's going on with testosterone in the life cycle? And is it – is there menopause, right? Is there such a thing as menopause for men? Is there a menopause? Okay. So, yeah, let's start there. So let's start with how testosterone moves over the life cycle.

23:18And if you look at a graph, and I think I'm looking at the NHANES, which is the National Health and Nutrition Examination Survey, is a nationally representative survey that the CDC runs. It's a really good source for a lot of the biometrics that we have. Normal values. Over time, because exactly like they they unlike many other surveys, they actually test people. They bring them into these like like drive around these mobile clinics and participants like come to the clinic and have their blood drawn anyway. So this will show you testosterone over the life cycle. And there is one really striking thing in these graphs, which I'm looking at as we talk, which is, you know, between the ages of like six and, you know, 20, your testosterone goes from more or less zero to like 500.

24:13And this is like in what is it? Is it nanograms for deciliter? Nanograms for deciliter. Yeah. For deciliter. So at any rate, you start with none. little kids have very little testosterone, and then you go up a lot during the period of puberty. So it's very clear. Testosterone is very important for driving the changes that we see in boys during puberty, the development of secondary sex characteristics, the starting of spermatogenesis, et cetera. And then you see it over time. And honestly, Perry, I'm looking at this graph, and it looks like it looks like.

24:46Emily Oster:I knew you were going to say that when I put the graph in our research document. Yeah, you sort of, so this graph shows the sort of variation in testosterone levels. And let's just put some numbers on it because we'll kind of keep coming back to this. In adult males, so post pubescent males, most values tend to run between 300 nanograms per deciliter and a thousand. Most people would draw the line at 300 nanograms per deciliter to be like low testosterone or like lower testosterone. There is no cliff. This is not estrogen for women going through menopause, which is kind of up there and just like tanks at menopause.

25:30Emily Oster:It is relatively flat. Now, if you mathematically model this and account for things And, you know, you can show in a large enough population that there is an age-related decline in testosterone. On average, this is the same NHAIDs data using mathematical modeling. The kind of average goes from about 400 nanograms per deciliter at age 20 to about 300 nanograms per deciliter at age 80. That's a change, but it's not dramatic. So menopause. Also, I just have to say I'm looking at this graph, and this graph is so obviously – this is like – we might need to take this out of the podcast. But this graph is so obviously driven by somebody overfitting a line to a very small amount of data on old people that I can't even – There's confidence intervals here.

26:22For those of you who love an overfit, this graph is an overfit. Emily's not convinced.

26:25Emily Oster:Okay. It's an overfit. Emily's not convinced. How about this? data does suggest across multiple populations, both in the U.S. and abroad, that average testosterone levels in the population have decreased over time. So not only is we've gotten older, but like a 50-year-old man today has a lower testosterone than a 50-year-old man in 1980. Levels have been going down, they say, by about 1 % per year. Depends how you model it. Do you buy that? Yeah, I think that's interesting and we should come back to it because I think it's part of understanding why this has declined. But I would say first, if we ask the question like, is this like estrogen?

27:09Relative to estrogen where we talked about there's really this period in which it declines quite a lot and which replacement is helpful, we're not seeing that in testosterone. So it doesn't necessarily mean you wouldn't get something from supplementation, but it's not the case that there's some period of your life when your testosterone is just tanking.

27:25Emily Oster:That's right. You can be an 80-year-old man and have a testosterone level that a 30-year-old man has. But, like, I challenge you to find an 80-year-old woman not on estrogen supplementation that has an estrogen level of a 30-year-old woman. Like, that does not happen. OK, so but we also know from this amazing enhanced graph that there is a lot of variation within age. Right. So the if you look at like the 10th percentile of people, say, at 40 to 49, they're at about 200. The 90th percentile is at about, I don't know, six to 700. And so that's a really big range. And I think that that relates to the question of like what what determines this?

28:06How do you get to be a person of a testosterone level of 700? And realistically, and I'm just going to channel the influencers here, how do I get the 700? What do I need to do to optimize my testosterone, Perry? Not me specifically. I have only a small amount of testosterone. What do you need to do? What are you doing? What do I need to do? Perry, to optimize your testosterone. Yeah. And I mean, they're like all things. I've stumped you. You're not doing anything?

28:37Emily Oster:I'm actually not doing anything, but I'll give you some things that you can do to optimize your – or let me phrase it this way. I will say that before we decide whether we should make some number higher, we should decide whether it matters to make that number higher. But because we just talked about variation, I will tell you what we know, what correlates with lower levels versus higher levels in the general population. Age is one. It's not as powerful as you think, right? But there is a statistically significant correlation between age. A history of smoking lowers testosterone. Current smoking, which is really interesting, will actually increase your total testosterone level by, and this actually might explain why total testosterone levels have gone down over time.

29:27Emily Oster:Can I detour for a second? Because this is very weird. You can detour. That's weird. Okay. So testosterone is broken down very quickly in the blood. has a half-life of about 10 minutes to maybe 60 minutes, depending. So it's carried around the blood by a chaperone protein called sex hormone binding globulin. And that kind of protects it. It like wraps testosterone in a little hug and keeps it safe from being degraded. But it's also inactive. Testosterone in that bound form can't do anything. It has to be free. Free testosterone is the active form. That's about 2 % of total testosterone. But most people, if you're getting your lab test measured, and all the numbers we've said so far are total testosterone numbers because free testosterone is a very difficult test to run.

30:09Emily Oster:It's expensive. There's a couple different assays. None of them are FDA cleared at this point in time. So most people are getting total testosterone. If you increase sex hormone binding globulin, you'll increase total testosterone because you just kind of have more that's out there stuck to the chaperone protein, but it's not actually doing anything. And current smoking does that. So there is some possibility that the reason we see this generational decline in total testosterone is actually because we're smoking less, which is a really sort of paradoxical and fascinating finding. Why would having a history of smoking make your testosterone lower?

30:50Emily Oster:I think that's just comorbidities. So the other stuff on the list for making your testosterone lower is like higher BMI, depression, diabetes. These are all things that kind of go along with smoking, obviously cancer, right? So I think the history of smoking is just like you've kind of – if you put your body through the ringer. Testosterone also is a hormone that has a pretty fascinating response to your psychosocial state. So there's a well-studied phenomenon that if a man wins something, their testosterone level goes up. So if you measure soccer players before the championship game and you do their salivary testosterone and then one team wins, one team loses, the winning team will have a significantly higher testosterone after the game.

31:38Emily Oster:This doesn't last for very long. This also carries over to men watching their favorite sports teams. so if you are you know an Eagles fan Jalen Hurts runs it in for a touchdown your testosterone might go up a little bit so it is it is quite a cerebral thing don't you think that's a that I mean that feels like an evolutionary adaptation right which is like the moment that I win the fight with the other guy that's the moment that a lot of the lady animals the lady monkeys want to have sex with me And so I want to be like in a high like testosterone environment. So I'm like ready for the lady monkeys after the soccer game.

32:16Emily Oster:I mean, yeah, I'll buy it. I'll totally buy it. I don't know. I'm not an evolutionary biologist. It makes sense. Right. I know. But I think evolutionary biology is just like telling stories like that. It's just some of it. Some of it. Some hypothesis generation there is that kind of story. And that's the story I'm going with. I totally love it. Did you lose your train of thought? No, of course not. Because I have one other thing that has been shown to temporarily increase testosterone, which is watching erotica or sexually charged visual imagery. Men are simple creatures, Emily. You like to win soccer and watch porn.

32:48And those are the activities that you enjoy.

32:51Emily Oster:As I was reading about this and comparing it to like estrogen in women and it's like so complicated and like how, you know, what's going on. Soccer and porn. Things we like. Soccer and porn. Doesn't take much. No. But there is a lot of between-person variation in testosterone, and there is also within-person variation in testosterone. Emily, one of the things that came out when I was looking at how testosterone is measured is this fact that the coefficient of variation of testosterone measurement is 50 % or higher within a man. Can you, with your data hat on, explain what coefficient of variation means?

33:33So a coefficient of variation is technically it's the ratio of the standard deviation to the mean, which is not that helpful for people. It's really a way to measure sort of how much something is varying, in this case, within a person's scale to the mean. So if something has a coefficient of variation of 50 percent, it varies quite a lot within a person over time. You know, many things would have like, you know, your weight within a time period does not have a coefficient variation, anything like that.

34:09Emily Oster:Exactly. And so, you know, just to put like a number on it, roughly, we could say like, OK, if your testosterone is kind of on average is 300, you get it measured one day. Maybe it's 450, right? Maybe it's 150 another day. Let me play you an influencer that I think speaks to this potential problem with testing. I increased my testosterone by 48 % in only 21 days without medication. Here's how. I'm not even going to tell you how. Is it that he tested again, though? So that's the thing I want to get out. When someone says, you know, my whatever it is, my testosterone, anything that went up dramatically, you have to know how variable it is at baseline.

34:54Emily Oster:And testosterone is highly variable. We know for one thing, for example, it's about 15 % higher on average in the morning than in the afternoon. So like men's testosterone is just higher. But that's like averaging across thousands of men. Within a given man, if you test today and you test a week from now, you're going to get very different numbers. And that is going to have the effect, because we're all human, that you will start to assign causality to things that you did to make that change when there is, in fact, nothing. The recommendation from endocrinologists is, in fact, that you don't diagnose low testosterone without at least two measurements, temporally separated, that are both below 300 nanograms per deciliter.

35:40So one of the reasons to keep I mean, I think that that influencer clip is, you know, it's interesting from the coefficient of variation standpoint, but it's also interesting because, of course, this guy's on the Internet saying how great his testosterone is. And that's like as a marker of, you know, whatever positive manhood, presumably, which gets to the question of whether, in fact, we see like are there symptoms of low testosterone, either low or just intermediate? Like if you told me I've been tested many times and my testosterone level is 500, should I expect you to be better on some dimension than if your testosterone is 400?

36:22Emily Oster:Yeah. That's my question. This is the question, okay? Because we're so tempted to look at numbers and be like, higher number is better. And we do this with so many things, right? We do this with like vitamins. We do it with protein to some extent, right? Like we're trying to max everything. Let me play you another influencer clip. I'm ready. Oh, man is normal in a 300 testosterone range. Your quality of life is gone. And it's like you said, it's not just libido. You're not going to be able to lose weight. You're not going to be able to gain muscle just like you just said. You're going to be feeling like you can't focus on anything.

36:59Brain fog, like to no end. You're also going to ache.

37:02Emily Oster:You know that. You're going to ache. You're not going to be able to move well. Every little thing you do is going to hurt. It's going to be painful. That sounds terrible. Terrible. It sounds pretty bad. I don't want to have a testosterone level below 300. So how – but is it actually true? Let's walk through the EMAS study from the New England Journal of Medicine because I think this is the one – this is like how you would design a study to assess what the effects of differing levels of testosterone are. So this was a survey-based study, 3 ,369 men ages 40 to 79 in Europe. And they gave them very long questionnaires asking about a wide variety of symptoms, depression, confusion, brain fog, fatigue, sexual symptoms, on and on and on.

38:00Emily Oster:After giving them all those questionnaires, they measured their testosterone level, right? And this is what you would want to do. Using a blood – like for real. Using a blood test. They measured with a blood test. Yeah. So it's like, OK, this is, you know, it's one thing to say, like, I measured my testosterone and it was 250. And now I attribute everything that's bad in my life to that to that number. That's sort of like astrology. Right. It's like it's like I'm a Libra. And like, so that's why you can't trust me or whatever. I actually I don't know. Is that true about Libras? I could not. So it's not really my thing.

38:31Emily Oster:That's probably because you're a Virgo. I'm an Aquarius. Yes. Okay. Should have known. No, but that – okay. So this study instead says, like, look, there are going to be people who have depression. And are there more people with depression out of low testosterone? Or is it just something that, yes, of course, people with low testosterone have depression and people with high testosterone have depression. So, Emily, was there anything that stood out to you in the results of this study as like what, if anything, is it clear that lower testosterone causes symptomologically, symptomatically? So the statistics in this study are a little like a little tortured for the sort of basic reason that they're doing a tremendous number of different tests and running them in various ways.

39:19So the like sort of some of the key results that that show up as significant, they're kind of picking a threshold and then estimating the impact as you sort of move below that that threshold. But of course, there's a tremendous amount of choice that goes into like, well, what is the threshold and exactly how do you structure it? And if you're kind of like, you know, messing messing around, you can get closer to significance. And they're testing many things. I will say the thing that sort of shows up most consistently here is stuff about sex. So sexual thoughts, mourning erections, erectile dysfunction, those are the key things.

40:01The effects are not that big, right? So like it's a little hard to exactly translate their number into something that would be meaningful for a person. So it's like, what's the odds ratio when you move one nanomole per liter below the threshold? Who knows what that number means? But the effects are small and not very significant, is my read.

40:23Emily Oster:Yeah. I mean, even it's very hard to actually assign like good numbers to decreased sexual thoughts, right? It's like, how often are you thinking about sex? Like there's all those sort of urban legends and stuff like that. But yes, to me, it's very clear. They looked at, you know, 50 different potential symptoms. And the only things that sort of withstood, however tortured the statistics are, the only things that sort of stood out were things about sex. So, yes, it does seem like if your testosterone is lower, your sex drive and things associated with sex drive is going to be lower. But notably, the psychological symptoms had no correlation with testosterone level.

41:01Emily Oster:So these influencers who are like, oh, if you're below 300, you're going to be essentially on your deathbed. You're going to be in pain. You're going to be depressed. You can't think straight. You have no energy. Like that is not borne out in the data where people are blinded to their testosterone level, right? Like you can make the argument after the fact. You can kind of attribute it, but you're probably incorrect. Yeah. I think the other thing about this trial and even about these results is what they're looking at is sort of what is happening as you're moving down below some lower threshold, right?

41:31So here we're like really very focused on this question of if you are like these influencers saying, OK, if you're below 300, what happens to you? Again, there's no cliff. But most of these trials are about these lower, like moving down within lower levels, not asking the question of whether 700 is better than 600. Oh, yeah. And for that, I think we just have no way. There's no evidence to suggest that's true.

41:58Emily Oster:Yeah. And I would be very honestly, I'd be very surprised if it's true. And the variation within a person, you know, if you're below 700, if you're 650 today, you're 750 tomorrow, you're 600 the next day, like, you know, you're only going to see effects when things are low. And again, it looks like those effects are fairly limited. But that was an observational study, right? That didn't say anything about replacing testosterone. So there's, okay, if you don't have enough testosterone, All right, you have decreased morning erections and a higher risk of erectile dysfunction. Then the question is, OK, what if we replace testosterone?

42:34Emily Oster:Do those things get better? Do other things get better, too? And in this case, we really don't want influencers to tell us what their anecdotal experience was. We want to hear in the form of randomized trials, right? We want placebo controls where people don't know they're getting testosterone because we've said a million times. If I tell you I'm giving you testosterone, even if it's not, it's like Felix Felicis in Harry Potter, right? You're just like you feel good and that's the power of placebo. And this is such a classic place where the placebo effect is going to matter tremendously because if you tell somebody, you know, I'm giving you something and it's going to make you feel more excited about sex, like they are going to feel more excited about sex for sure.

43:21There's just like no question. So much of this is in your head.

43:24Emily Oster:Yeah, yeah, yeah. That's how oysters work. Exactly. So let's – we can't obviously talk about every trial, but I think there's a couple that are relevant to the discussion. The testosterone trials, the T trials enrolled 788 men above age 65 who had total testosterone less than 275. Can I just ask you before we get into – like what do you think about focusing only on older men in this? Do you wish that they had focused also on people like you? I think they would not find the signals that they want. I think it would be very expensive. So the truth is if you're enrolling people with normal testosterone levels, you're not going to get any signal with physiologic levels of replacement.

44:06Emily Oster:By the way, everyone knows, right, that like anabolic steroids that bodybuilders use are testosterone, right, or synthetic forms of testosterone. People know that. Yeah. I'm not sure people know that. Let's tell them that. Anabolic steroids are a synthetic form of testosterone. Yeah. They just happen to be given in like 10 times the dose of testosterone replacement therapy or even up to like 30 times the dose. So these are crazy super physiologic doses of testosterone. And I think, in fact, some of the hesitancy, to get to your point, Emily, about testing and giving men testosterone replacement therapy comes from the complications that have been seen in bodybuilders.

44:39Emily Oster:Because we know that when you're giving 10 times the normal rate of testosterone, you You get infertility, liver failure, roid rage, baldness, cardiovascular disease. Like all this bad stuff happens. But just because that happens at 10x the dose doesn't necessarily mean it happens at 1x the dose, right? Like the dose is the poison, as the toxicologists like to say. So I think that has, you know, actually hampered this research a little bit. All right. So getting back to the testosterone trials with the older men. these focus on people who have testosterone in lower levels. So I think the criteria here was below 275.

45:18So people who are in the range of the, you know, below 300 and you're basically dead. And what happens?

45:27Emily Oster:What happens is your sexual stuff gets better. So these older men that were randomized, again, placebo-controlled, randomized to testosterone, had a 40 % increase in sexual activity, sexual activity frequency. A 25 % increase in their libido scores and a 35 % improvement in erectile function, but no improvement in vitality or energy and only very small improvements in mood and walking distance. And this is something that like gets repeated. I've seen this again and again. And, like, if you look really at – if you ignore the influencers who say, I started taking testosterone replacement therapy and everything was a miracle, what you hear from men is, like, sex, sex, sex.

46:09Emily Oster:I looked at a Reddit thread in the AskMen. It's a sex hormone. It's a sex hormone. There's a great Reddit thread in the AskMen subreddit. It was, like, anyone taking testosterone replacement therapy? Like, how was it for you? And the basic breakdown is like 20 % of people being like, I took it and actually I didn't feel much. 20 % of people are like, I took it. My life is great now. Like I feel so much more energy. I feel young again. Great. And 60 % of people are exclusively talking about like the quality of their erections and how horny they are. with one amazing comment blaming testosterone replacement therapy for the failure of his marriage because – He wanted more sex and she didn't.

46:58Emily Oster:Exactly. Yeah. Something that has come up on this podcast before. Emily has suggested that, you know, women have a lower sex drive than men. And I tried to be offended and I couldn't. And the data tends to bear Emily out. Data shows. Data shows it. So be careful if you're taking testosterone replacement therapy. You might want to discuss it with your significant other. You should always talk about this stuff. Yeah. Yeah. I mean, I think, you know, look, when you look, the picture here feels very clear and almost it's an example where you're in this rabbit hole of influencers. And if you just pull yourself out and you're like, OK, let me just think about like what is likely to be true based on what we know about this.

47:42it seems likely that the thing that is going to happen is about sex because that is and about feelings about sex because that is like the core thing about testosterone is that it has all these things to do with how you feel about sex and how much you want to have sex and your ability to have sex and all these other all these other pieces just like it feels like that is very sensible in contrast to a claim like you won't be able to walk or move very well which there's really no reason to think testosterone would have anything particular to do with. Yeah. And I mean, insofar as mood maybe does improve slightly, like we can even draw a line

48:23Emily Oster:between the sexual effects and those subjective effects on mood and energy and whatnot. I mean, maybe not for the guy whose whole marriage fell apart because of sexual incompatibility, But you can certainly imagine that if all you do is increase sex drive, like for many men, that might be enough to feel a little bit better about things, right? Totally. So if people are not interested in taking exogenous testosterone, I mean, there are a couple of places where it seems like there are small impacts of lifestyle changes on testosterone, mainly around weight loss is what I would say. Like there is some evidence of small amounts of increases in testosterone as a result of weight loss and similar with, you know, GLP-1s, which is presumably for the same reason.

49:15Those are, again, like those are actually – those effects are pretty small, smaller than I might have thought that they would be actually.

49:21Emily Oster:Yeah, me too. We usually see sort of better effects with significant weight loss in other domains. Yeah, absolutely. That is actually one of the reasons as I was kind of looking through this and deciding what my feelings were about testosterone replacement therapy, I tend to constitutively be like, oh, like let's find lifestyle things that can improve the thing first rather than just like supplements or, you know, doing it exogenously. And the truth is that there's not a slam dunk here. Again, you're going to see some people telling you that like there's really easy natural ways to increase your testosterone.

50:00Emily Oster:Here's a guy talking about zinc. If your libido is gone and your energy is tanked, you might not have a hormone problem. You have a zinc problem. Your body cannot build testosterone without zinc. Today we're libido maxing at Whole Foods. We're libido maxing. I love it. Please don't do it at Whole Foods though. Why? I know Whole Foods. I don't want a bunch of people libido maxing while I'm just trying to buy salmon. It's cheaper just to buy the testosterone. Is that true about the zinc? In what way is zinc related? This is like classic mechanism jumping to conclusion problem. So yes, zinc is a cofactor in the synthesis of testosterone.

50:42Emily Oster:In the biosynthetic pathway of testosterone, you need a little bit of zinc. That does not mean that getting your zinc level crazy high increases that. It's like it's a vitamin, right? Or it's a mineral. But like, you know, you need some amount or else you can't synthesize testosterone. But having more doesn't mean you synthesize more. About 8 % of the United States is zinc deficient. But this is largely people with significant comorbidities who are older and who don't have access to adequate nutrition. You, listener, are probably not zinc deficient. And pumping up your zinc level is not going to really increase your testosterone.

51:19Emily Oster:Although, again, if you check it a couple times, you're going to get numbers you like. It's like taking the SATs over and over again. Totally. I was just thinking. It's like take it again, take it again. Right? They only count one of them. And I will say that if your zinc is too high, then your copper metabolism can get thrown off and maybe you don't get enough copper. I don't know. So don't stress about stuff like that. I think the real question for people when they're considering testosterone replacement therapy is really quite simple. Is my endogenous testosterone low and is it really low? Like did I get one value that was low and all the others are normal?

51:52Emily Oster:Is it consistently below 300 on multiple tests? And do I have sexual symptoms? Yeah. And if the answer to either of those is no, like there's not much to be done. I'm going to add to the last thing. Like do I have sexual symptoms that are a problem for me? Because I think actually when we talk about sex here, it's like, you know, we're always talking about this like your goal is to want more sex. And like maybe that is that is your goal or I'm being bothered by not having the libido that I want. And I think that if that's true, that's absolutely a consideration. I think people should ask, always ask the question like, is this something that's actually a problem or not?

52:29Emily Oster:Yeah, yeah, yeah. Very important. What about risks here at the kind of dosage levels that we see obviously at very high dose levels like you would have an anabolic steroid? There are many issues, acne, weird hair in different places or not enough hair. Strokes and heart attacks. Strokes and heart attacks. Liver failure. Being caught by USADA for doping. But what about for people outside of this at a normal dose? Yeah. I mean, the major concern has always been cardiovascular disease. Again, I think largely driven by the bodybuilding community. In fact, the FDA mandated a trial in higher risk older adults of testosterone replacement to see.

53:15Emily Oster:This was a trial called TRAVERSE, more than 5 ,000 people, randomized trial for testosterone replacement therapy to look for cardiovascular disease as an important outcome. And actually, there was no difference in major adverse coronary events in that trial. Again, you'll see influencers who are really pushing TRT being afraid of the cardiovascular risks. The TRAVERSE trial repudiated this. But no one trial is perfect. I mean, you'll hear Traverse, Traverse, Traverse. No one trial is perfect. The follow-up was 33 months in that trial, which is almost three years. But that doesn't mean that stuff can be going on.

53:54Emily Oster:that gets you 10 years down the line. And I will say, if you actually dig in, if you actually read the TRAVERS trial, what you'll find is that there was a higher rate of atrial fibrillation, which is that abnormal heart rhythm that actually endurance athletes like yourself, Emily, are at higher risk for. Yes, thanks. And blood clots in the testosterone arm. Low, you know, the absolute risk was very low, but it was higher than in the placebo group. Other risks that I think are, you know, worth considering. One is fertility. So testosterone supplementation, if you are trying to become, not become pregnant, get someone pregnant, if you're trying to get someone pregnant.

54:35Contribute positively to pregnancy, yeah.

54:37Emily Oster:Yeah. Testosterone placement can decrease the production of sperm. There are issues with acne and hair loss. And then prostate enlargement, but probably not prostate cancer. So benign prostatic hypertrophy, which is just a benign enlargement of the prostate, can make it a little hard to pee. That's been shown. And then I've got a fun bit of chemistry for you, which is that testosterone is metabolized in fat cells to estrogen, to estradiol via an enzyme called aromatase. And this is why people on very high doses of men on high doses of testosterone can develop gynecomastia, which is the development of like glandular breast tissue as popularized by Robert Paulson in Fight Club for the Gen Xers played admirably by Meatloaf.

55:31Emily Oster:So there is a risk of gynecomastia from testosterone supplementation, and it is higher if you have a higher body fat percentage because that's where that conversion to estrogen takes place. Okay, I have one last urban legend to discuss before we smash or pass, which is the ratio of index to ring finger. So there's like this idea that if you have a long ring finger, I think it's right, that that indicates a high level of testosterone. Yeah, this is also all over Instagram. Take a listen. Your finger length reveals how much testosterone you were exposed to in the womb. Hold your right hand up. If your ring finger is longer than your index finger, you had high prenatal testosterone exposure.

56:21Emily Oster:If they're the same length or your index is longer, you had lower exposure. This ratio is called the 2D-4D, and it's one of the most studied markers in human biology. Okay, so I don't know that this is one of the most studied markers in human biology, but boy, if I didn't look at my own fingers. Did you – your fingers seem like you're in trouble. Well, I feel like depending on kind of how I hold my hand, I can kind of make it do – no, I don't know. Maybe I didn't get enough testosterone. What does that even mean? This guy goes on – I'm not playing the whole clip, but he goes on to say like, oh, then if you had more testosterone in the womb, you're like going to be more aggressive in life.

57:03Emily Oster:And I don't know. Emily, you were saying there's some – There's a fair amount of literature. This is just a bunch of bullshit. But I like so I haven't I'm looking at a meta analysis of this, which here is the key statement. We found no evidence of the relationship between the testosterone types and digit ratios. Furthermore, there was no evidence in very so this is there is no evidence of this. Maybe it is very highly studied, but very highly studied to conclude that it is fake. That's he should have added that he should have. This is very highly studied and we've concluded it's garbage. I mean, even if true, I don't see just like how this matters aside from, I don't know, making conversation at parties or something.

57:45Okay. Perry, I'm going to ask you a personal question. Yeah. Do you know your testosterone level?

57:49Emily Oster:No. You didn't even test it for this episode? I don't – how much – I don't have whatever it is. I know my testosterone. I know my testosterone. Oh, what's your testosterone? 25. Okay. It's like – it's not – it's below 300, but I don't know. It's part of this like blood panel. Part of some blood panel I've got. I don't know. It said it was sufficient. That seems entirely normal for a woman. Sufficient. It would be low for me. No, I mean, I haven't had it tested. It's one of those things where I don't have symptoms that I would attribute to low testosterone. And so even if I had it tested and it was low, I don't know that I would necessarily want to do anything about it.

58:30Emily Oster:And that's always our threshold for should I check something is the answer going to make a difference. I also feel like what if you tested and it wasn't, like it was like 400, and then you were like, ah, now I have to get it tested again so I can try to – because you're not really like me, so you probably wouldn't do that. But I feel like that's the reaction I would have. I'd be like, oh, what can I do? Yeah, I mean sometimes just like knowledge is – ignorance is bliss. Ignorance is bliss. All right, Perry. Testosterone supplementation. Smash or pass? Pass. I'm giving this a smash for men with low testosterone levels who have sexual symptoms.

59:06Emily Oster:Otherwise, it's a pass. Emily, smash or pass? I concur. Smash if you have low levels and it is bothering you. Otherwise, pass. All right. That is it for testosterone, your mailbag question of the week after the break. Who doesn't love warm, carby comfort? satisfying sandwiches, loaded bagels, rich mac and cheese. Crape-worthy and smart, Hero Bread's loaves, bagels and noodles have just 0-5 gram snack carbs, 0 gram sugar and up to 19 grams of protein and 32 grams of fiber per serving. Hero Bread bakes with heart-healthy olive oil and delivers a soft, fluffy, flavorful experience you love. Shop now on Hero.co.

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1:01:29Hi, Emily and Perry. This is Emily also from Baltimore. My husband is newly sober, so I kind of am now too. My question is, what is the health impact when swapping a daily alcoholic drink for a daily soda? And what's the impact of soda versus diet soda? In other words, if the choice is a daily drink of alcohol, diet soda, and regular soda, is there a clear winner health-wise? Love the show. Thanks so much. So you're asking the question about alcohol, diet soda versus regular soda. This feels like a fairly straightforward answer, which is if we're kind of thinking about some kind of optimizing.

1:02:08Diet soda is the winner. It doesn't have the sugar and it doesn't have the alcohol. That's different from saying that you can't have like a healthy lifestyle that incorporates alcohol or regular soda in it in moderation. But if you're telling me like I'm indifferent between those three things, I'm going with the diet soda.

1:02:25Emily Oster:Yeah, I totally agree. I mean there is a lot of concern out there about artificial sweeteners. In fact, that is on our list of upcoming episodes somewhere. Our producer Tamar can tell us where that is happening. But much of this, as you will see in that episode, is really overblown or hypothetical concerns. If mice exclusively eat sucralose as their entire diet forever, that's not ideal. Right. And, you know, but the concerns we have about alcohol and about, like, sugar or corn syrup, as you would find in regular soda, is much better documented, much higher level of evidence. So I think there's a lot of anxiety about artificial sweeteners, diet soda.

1:03:11Emily Oster:Water is probably better for you than drinking that stuff. But if you're purely talking about health risks, definitely diet soda over alcohol if you get the same sort of amount of joy out of it. Yeah. I mean I think that point about joy is important because I think certainly – I've spent a lot of time with the alcohol and health literature. and, you know, occasional light drinking is, I think, the potential negative impacts are really quite small relative to some of what you hear. But, again, if you're saying, like, I'm totally indifferent, I think this is a clear call, particularly because this person has specified that, like, this is what works for their relationship and is supportive of their partner, which makes it an even clearer no-brainer.

1:03:55Emily Oster:And also, have you tried Diet Dr. Pepper? Amazing. It's great. It's too sweet. I find it too sweet. But like a nice Diet Coke, like for me, that's like, cannot beat it. Fridge cigarette. That's what Gen Z calls that, the fridge cigarette. Well, that's it for us today. Stick with us next week when we'll ask, what's the deal with colostrum? Wellness Actually is produced in association with iHeart Media. Our senior producer is Tamar Avishai. Our executive producer at iHeart is Jennifer Bassett. Our theme music is by Eric Deutsch, and our content is for educational purposes only. If you like the show, help other people find us.

1:04:37Emily Oster:Leave a rating and review on Apple Podcasts or your podcatcher of choice. And help us spread the word about the show. You can follow us on Instagram at wellnessactuallypod. And don't forget, we want to hear from you. Head over to wellnessactually.fm and leave us a question for our mailbag or suggest a topic for a future show. We'll let the influencers have the last word. Yeah, testosterone replacement therapy, hormone replacement therapy, yeah, it makes a big difference. Makes a big difference. Fuck yeah. There's a stigma attached to that in a lot of people. Like, you know, where do you get your testosterone from?

1:05:10I'll get it from my balls.

1:05:14Emily Oster:It's real simple. If you're fine with not feeling as good, good. Go ahead. Stick with that.

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