Testosterone – Science Sushi

Mythbusting 101: bulking up with bull shark testosterone

This week, the startling image of a 1,000 pound bull shark has been circulating the internets. But what really caught my eye was the quote from the lead researcher. He told news outlets that bull sharks “have the most testosterone of any animal on the planet, so that should tell you a little something.” Tsk tsk. No matter what those websites tell you, it’s simply not true.

This isn’t the first time I have heard this whole bull sharks and testosterone bit. Indeed, all over the internet, you see claims that bull sharks are so aggressive because of their insane testosterone levels. But it was the character Bruce Kibbutz in Grand Theft Auto IV that really got people talking about bull shark testosterone. During the game, the roid-raging fitness freak explains how he juices on testosterone taken from Chilean bull sharks. Suddenly, extreme body builders and skeptics wanted to know if you could really bulk up on bull shark blood.

The rumor, as I’d heard it in college, is that the fierce attitudes of these large and aggressive sharks is due to unfathomably high circulating levels of testosterone. Specifically, these menacing monsters supposedly have higher serum testosterone levels than any species on the planet, land or sea, and that even a female bull shark has higher levels than a testosterone-raged male elephant in musth. I know I’m as much to blame as anyone, as I’ve repeated that line myself. But when I was asked about it, I realized that I didn’t know if it’s true. How do the circulating testosterone levels compare between bull sharks and other species? Could you procure enough testosterone by catching and eating bull sharks to beef up your body?

Let’s start with that elephant. In the red corner, standing up to 11.5 feet tall and weighing in at up to 20,000 lbs, we have the African Bush Elephant (Loxodonta africana). What’s the testosterone level in this whomping beast? During much of the year, not much. Male elephants, on average, have less than 2 ng/ml ciculating in their plasma. But wait! Big boy wants to get his groove on, and he is getting ready for a season of fighting and fornicating. So what’s the male elephant in musth’s testosterone level? As high as 64.4 ng/ml! About a 60 fold increase in average circulating testosterone¹. Ai! That’s a lot of anger-pumping hormone.

How about his opponent, the every day female bull shark (Carcharhinus leucas)? In the blue corner, weighing in at around 505 lbs and stretching almost 12 feet long, is our large and in charge girl. She’s bigger than her man, no doubt, but she still has to keep her femininity about her. After all, as a girl, if her testosterone levels are too high, she might have reproductive issues. Surely her circulating levels are lower than the male elephant’s?

According to the only, extremely obscure published reference with testosterone levels in a female bull shark, actually, yes, they are². Her circulating testosterone level is right around 0.1 ng/ml, a whole lot lower than that angry elephant. Sorry to burst bubbles, but she ain’t gonna give anyone roid rage. Her man, though… My oh my. One of the two male adult bull sharks in that study had a circulating testosterone level of 358 ng/ml. Yeah, that’s one roided out shark. Problem is, the other male bull shark in that study only had 2.7 ng/ml of testosterone in his serum – which is probably less than you male readers out there have pumping in your blood right now. So not all male bull sharks are running around roided out of their minds. To be fair, these were just single sharks, caught once and tested once. Without a more complete study of the average hormone levels in bull sharks, by size, season, etc, we can’t really say that bull sharks have abnormally high or low testosterone levels.

Of course, there is a more complete study. Not a super detailed one, but a study none the less. Rasmussen & Murru³ studied androgen levels in a number of captive sharks over time. They found testosterone levels of 10 ng/ml to 20 ng/ml in two captive bull sharks when they measured every June for three years, just after the sharks’ normal breeding season. Not too impressive, boys – not too impressive, but of course, that is in captivity, and it’s unknown how captivity may affect their hormone levels.

In wild bull sharks caught right before the breeding season, the serum levels were much higher: 185 ng/ml on average – which was 4 to 10 times higher than the levels they found in two other shark species, and is pretty impressive compared to the elephant. But, it turns out, it’s not that hard to find high testosterone levels in fish. Other sharks have high levels, too – like the bonnethead, Sphyrna tiburo, whose highest levels have been recorded at 303 ng/ml⁴. And in that species, even the girls have higher levels than our elephant – a whopping 74 ng/ml at max⁵. Believe me, I’d rather go hunting bonnethead than bull sharks any day. Other fish, too, have been found to have high testosterone. Male rainbow trout have levels around the same as those of the bonnetheads⁶, and heck, they sound a whole lot tastier to me than the other options. Just sayin’. Sorry folks, but according to the best, albeit limited scientific information we have, the idea that bull sharks are super juiced-up compared to other animals just isn’t true.

Yet in the news and even on the Discovery Channel’s infamous Shark Week, the highest-testosterone-in-the-world bull shark is the norm. How did the data end up so skewed towards this single result? As I see it, it is the scientific community that is to blame for the impression that bull sharks are testosterone-pumped. Every other paper I read about shark hormones since the two with bull sharks cites them, specifically mentioning 358 ng/ml and that bull sharks have much higher levels than other sharks.

Now that I read the papers, I see it’s not the media’s fault. It’s the original authors that claim that bull sharks have higher testosterone than other sharks, even without presenting evidence to back it up. It started with how Rasmussen & Gruber were quick to point out how high that 358 ng/ml value is, saying it’s “among the highest recorded in vertebrate serum,” but didn’t talk at all about why the other mature male bull shark (by their own identification) was more than one hundred fold lower. But it’s really Rasmussen & Murru (hmm… that first name sounds familiar), in their discussion, who seem to overinflate their own data. They state that “a species differences in absolute concentrations appears to exist because concentrations of testosterone in both wild and captive bull sharks were about two times higher than those in mature sandbar and lemon sharks” (emphasis mine). Yet their included figure showing the yearly serum concentrations for the two captive bull sharks studied clearly shows the levels between 5 ng/ml and 20 ng/ml, while the levels for the two captive sandbar sharks sampled at the same and different times of year range from 0 ng/ml to over 40 ng/ml! Two to four times higher in bull sharks? Where? When?!

But enough griping about inaccurate inflation of results. Let’s say, for a hypothetical moment, that there is a time of year, size, or whatever where you could go out with a shark hook and some dead fish and guarantee getting a big boy bull shark with upwards of 300 ng/ml in his system. It’s time to address the other part of the myth: Should serious users think about going fishing?

You’ll have one big fish to fry if you’re trying to get a nice dose of testosterone by ingesting sea creatures. First off, I hope you’re feeling vampiric. You want the blood, not the tissues. We don’t know anything about how much testosterone is in bull shark tissues, and besides, that super high amount was in the blood… so, yeah. Cheers. Second off, unless you’re planning on shooting up shark blood, you’re not getting the dose you think. Orally ingested testosterone is rapidly absorbed by the gut, but it’s also converted to inactive metabolites, leaving you with only 1/6^th the dose you took remaining in active form. That’s why pills and injections aren’t actually of straight testosterone, they’re of slightly modified chemicals that the body doesn’t metabolize as easily. It also means that to get the same dose from shark as you would from a prescription (or black market) pill, you have to drink six times what you think you have to.

So let’s say you want to replace that 40 mg pill you bought with bull shark blood. Even if you catch that one shark that had 350 ng/ml in his serum, that means you’ll have to drink down three cups of shark plasma to equal one pill. A shark tends to be about 12.3% blood by weight according to previous studies⁷ – that’s 6.8% blood cells and 5.5% serum, which has a specific gravity (weight per volume) of around 1.03. So say you caught an average bull shark, weighing only 350 lbs instead of the max of 500. He’ll have around 44 cups of blood in him, which is only 44% plasma, so you’ll need to drink 6.8 cups of blood per pill. So at 2-5 pills a day, that shark will only last you one to three days. Hey – I guess it’s legal. Though somehow, I don’t think athletes are going to get away with the old “I was just drinking shark blood” excuse just because of that.

Of course, all of that assumes that the majority of bull sharks are swimming around with high testosterone levels, which as the data reveals, simply isn’t likely. What’s worse, though, is that by perpetuating the idea of roided-out sharks, we’re giving credence to the idea that bull sharks are mindless killing machines with a taste for blood. While bull sharks are certainly dangerous animals, they are far from the angry maneaters they’re portrayed to be. Given that you’re still more likely to die from being struck by lightning that by a shark attack, and that there are probably hundreds of thousands of bull sharks in the Atlantic Ocean alone… I’d say the bull sharks are being pretty restrained.

Citations: 1. JAINUDEEN, M., KATONGOLE, C., & SHORT, R. (1972). PLASMA TESTOSTERONE LEVELS IN RELATION TO MUSTH AND SEXUAL ACTIVITY IN THE MALE ASIATIC ELEPHANT, ELEPHAS MAXIMUS Reproduction, 29 (1), 99-103 DOI: 10.1530/jrf.0.0290099

2. Harold L. Pratt, Jr., Samuel H. Gruber, & Toru Taniuchi (editors) (1990). Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries NOAA Technical Report NMFS 90, 143-155

3. Rasmussen, L., & Murru, F. (1992). Long-term studies of Serum Concentrations of reproductively related Steriod Hormones in individual captive Carcharhinids Marine and Freshwater Research, 43 (1) DOI: 10.1071/MF9920273

4. Manire, C. (1997). Serum Concentrations of Steroid Hormones in the Mature Male Bonnethead Shark,Sphyrna tiburo General and Comparative Endocrinology, 107 (3), 414-420 DOI: 10.1006/gcen.1997.6937

5. Manire, C. (1995). Serum Steroid Hormones and the Reproductive Cycle of the Female Bonnethead Shark, Sphyrna tiburo General and Comparative Endocrinology, 97 (3), 366-376 DOI: 10.1006/gcen.1995.1036

6. Scott, A. P., & Baynes, S. M. (1982). Plasma levels of sex steroids in relation to ovulation and spermiation in rainbow trout (Salmo gairdneri) Proc. Int. Symp. Reprod. Physiol. Fish, 103-106

7. Thorson, T. (1962). Partitioning of Body Fluids in the Lake Nicaragua Shark and Three Marine Sharks Science, 138 (3541), 688-690 DOI: 10.1126/science.138.3541.688

Note: this post is updated from a version posted on Science Blogs in 2010

Observations: Why do women cry? Obviously, it’s so they don’t get laid.

This week, a paper came out looking at testosterone levels in fathers. A whirlwind of poor journalism followed, which was beautifully smacked down by William Saletan over at Slate (aslo: see this great post on the topic by our very own Kate Clancy). But it reminded me of a similar kerfluffle that occurred this past January over a paper on the effects of sniffing tears. This was my post from Jan 8^th on that paper and the media surrounding it, which just so happens to look at the meaning of lowered testosterone levels in terms of evolution.

I don’t think Brian Alexander is a bad guy or a misogynist. He writes the Sexploration column for MSNBC, so sure, his job is all about selling sex stories to the public. He even wrote a book about American sexuality. But I don’t personally think he has a burning hatred for women, or views them as objects placed on this Earth for the sexual satisfaction of men. However, I very easily could, given how he chose to report on a recent study published in Science about men’s physiological responses to the chemicals present in women’s tears.

The headline alone was enough to make me gag — “Stop the waterworks, ladies. Crying chicks aren’t sexy.” The sarcastic bitch in me just couldn’t help but think Why THANK YOU Brian! I’ve been going about this all wrong. When I want to get some from my honey, I focus all my thoughts on my dead dog or my great grandma and cry as hard as I can. No WONDER it isn’t working!

I didn’t even want to read the rest of the article.

But I did.

It doesn’t get better.

Alexander’s reporting of the actual science was quick and simplistic, and couched in sexist commentary (like how powerful women’s tears are as manipulative devices). And to finish things off, he clearly states what he found to be the most important find of the study:

“Bottom line, ladies? If you’re looking for arousal, don’t turn on the waterworks.”

It’s no wonder that the general public sometimes questions whether science is important. If that was truly the aim of this paper, I’d be concerned, too!

Of course, Brian Alexander missed the point. This paper wasn’t published as a part of a women’s how-to guide for getting laid. Instead, the authors sought to determine if the chemicals present in human tears might serve as chemosignals like they do for other animals — and they got some pretty interesting results.

In many species, chemical signals run rampant. Scents, pheromones, and other chemical cues are deliberately and unconsciously given off to tell other individuals anything from “Back Off – MY Tree!” to “Hop on and ride me, baby!” But despite how common they are in the rest of the animal kingdom, the function of chemical signals in humans is hotly debated. Years of searching has yet to find human pheromones (no matter what those websites tell you), and while scent seems to play a role in communication in people, there is still relatively little knowledge as to what chemicals and why.

Given that tears are known to serve as sexual signals in mice, it isn’t strange at all that Noam Sobel and his team chose to look at the physiological responses to tears. The Israeli team designed an impressive and unbiased set of experiments to determine if the tears produced by women when sad elicit physiological responses in men separate of the visual or auditory stimuli of a woman crying.

To find out if tears alone acted as chemosignals, the scientists collected tears from women watching tear-jerkers, and as a control, compared their effects to saline rolled down women’s cheeks. Men sniffed the solutions without any knowledge as to what they were during a series of different experiments. In the first, men with a tear-soaked pad under their nose were asked to rate the sexual attractiveness and mood of female faces. While the smell of saline had no effect, men inhaling Eau de Tears consistently rated women’s faces as less attractive, though this had no impact on whether they found the faces happy or sad.

For the second experiment, men sniffed tears before watching a sad movie. While doing so didn’t affect their mood, the smell of tears did elicit a physiological response: men’s faces became more conductive to electricity, which happens when we sweat and is indicative of a psychological reaction. Furthermore, the men self-reported less sexual arousal, which was reflected in their bodies as a 13% drop in saliva testosterone levels.

But to really get to the meat of it, the team threw their male test subjects into an fMRI machine and scanned their brains for activity while sniffing tears. Researchers saw much less activity in the hypothalamus and the fusiform gyrus, both of which are thought to be involved in sexual arousal. All three experiments lead to the same conclusion: the chemicals in women’s emotional tears reduce male sex drive.

The real question, though, is why? Why do men’s testosterone levels tank at the smell of a woman’s tears? The overwhelming answer given by mainstream media (as Rheanna pointed out) is that tears just aren’t sexy. When women cry, so the journalists say, it’s a chemical signal that they don’t want to have sex. Because evolution is all and only about sex… right?

Sorry to burst their bubble, but even when it comes to evolution, it’s not all about sex. Selection also favors survival — because, you know, you can’t have sex when you’re dead*. Thus women’s tears are not necessarily evolutionarily intended to turn guys off. For example, Ed Yong brings up the hypothesis that tears might be used to downplay aggression. Think about it: we cry when we’re sad or physically in pain. In both cases, we’re more vulnerable. Getting others, especially angry men, to be less aggressive towards us in that moment could certainly be a benefit to survival.

Really, the idea that tears are intentionally used as a turn off is a hard sell to an evolutionary biologist. What benefit do women get from not having sex when crying? Does it somehow make them have healthier or more babies? Not for any reason I can think of.

There is, instead, an even more intriguing explanation, one that makes a whole lot more sense. Many who wrote about this paper (including Brian Alexander) mentioned that tears are known to contain a variety of compounds, including prolactin, the hormone which is responsible for making a guy cool his jets after he gets off. But prolactin does much more than ensure a guy stops going at it — it’s a hugely important hormone for nurturing behaviors. In fact, the connection between reduced testosterone and nurturing/bonding behaviors may be the real reason as to why men’s testosterone levels dip upon sniffing tears.

Numerous studies have shown that parental and nurturing behaviors are mediated by prolactin while inhibited by testosterone. For example, research has shown that prolactin levels positively and testosterone levels negatively correlate with a father’s impulse to respond to a baby’s cry. Furthermore, men’s prolactin levels spike and testosterone levels drop in the weeks before their partner gives birth.

It goes beyond babies, too. Decreased testosterone and increased prolactin are strongly implicated in establishing and maintaining relationships. Monogamous men have significantly lower testosterone levels and higher prolactin levels than their single brethren. Furthermore, studies have directly shown that artificially increasing testosterone in a double-blind, placebo-controlled setting makes men less generous to strangers and reduces a person’s empathy for others.

Perhaps prolactin or other chemical signals in tears are directly targeting and activating the nurturing pathway in men’s brains. Being taken care of or protected when in emotional or physical pain would definitely benefit an individual’s survival. Personally, I would like to see this study of tears replicated to determine women’s responses to the scent as well as men’s reactions when using men’s and children’s tears, as well as looking at the levels of prolactin, oxytocin, and other well-established bonding and empathetic hormones. My bet is the response isn’t limited to men, and isn’t limited to emotional secretions from women.

While Brian Alexander and the rest of the sensationalists seem to suggest the signal is “I’m not in the mood,” its likely that the message has nothing to do with having or not having sex. Women aren’t saying “back off” — they’re saying “help me.”

Why do I care so much? It’s not just that they got it wrong. It’s that their interpretation of research isn’t labeled as opinion. It’s that the vast majority of people who have any interest in science news are going to read inaccurate (if not downright insulting) news articles and think studies like this one are either misogynistic or frivolous. It’s that journalists like Brian Alexander undermine good science for the sake of attention grabbing headlines. And as a scientist and a writer, it’s a double insult.

Gelstein, S., Yeshurun, Y., Rozenkrantz, L., Shushan, S., Frumin, I., Roth, Y., & Sobel, N. (2011). Human Tears Contain a Chemosignal Science DOI: 10.1126/science.1198331

* I can hear the comments now, you sickos, so let me clarify: you can’t have baby-producing sex when you’re dead.

Also, thanks to Kira Krend for the thoughtful and hilarious discussion on this topic!

Other References:

Haga S, Hattori T, Sato T, Sato K, Matsuda S, Kobayakawa R, Sakano H, Yoshihara Y, Kikusui T, & Touhara K (2010). The male mouse pheromone ESP1 enhances female sexual receptive behaviour through a specific vomeronasal receptor. Nature, 466 (7302), 118-22 PMID: 20596023
Fleming, A. (2002). Testosterone and Prolactin Are Associated with Emotional Responses to Infant Cries in New Fathers Hormones and Behavior, 42 (4), 399-413 DOI: 10.1006/hbeh.2002.1840
Storey AE, Walsh CJ, Quinton RL, & Wynne-Edwards KE (2000). Hormonal correlates of paternal responsiveness in new and expectant fathers. Evolution and human behavior : official journal of the Human Behavior and Evolution Society, 21 (2), 79-95 PMID: 10785345
Burnham, T. (2003). Men in committed, romantic relationships have lower testosterone Hormones and Behavior, 44 (2), 119-122 DOI: 10.1016/S0018-506X(03)00125-9
Zak, P., Kurzban, R., Ahmadi, S., Swerdloff, R., Park, J., Efremidze, L., Redwine, K., Morgan, K., & Matzner, W. (2009). Testosterone Administration Decreases Generosity in the Ultimatum Game PLoS ONE, 4 (12) DOI: 10.1371/journal.pone.0008330
HERMANS, E., PUTMAN, P., & VANHONK, J. (2006). Testosterone administration reduces empathetic behavior: A facial mimicry study Psychoneuroendocrinology, 31 (7), 859-866 DOI: 10.1016/j.psyneuen.2006.04.002