Does vaping shrink your balls?
I mean, there is non-zero evidence for this, but don't get too excited
Some time ago, someone sent me this:
I know, generic ancient Rome/Greek right-wing back-to-nature type stuff, even hates on deodorants:
"Alright Emil, but these are cheap shots. What does the science say? Are there such "studies show" as mentioned?"
Well, yes, sort of! Challenge accepted. One guy in the replies links to a useful review:
Szumilas, K., Szumilas, P., Grzywacz, A., & Wilk, A. (2020). The effects of e-cigarette vapor components on the morphology and function of the male and female reproductive systems: a systematic review. International Journal of Environmental Research and Public Health, 17(17), 6152.
E-cigarettes, a comparatively new phenomenon, are regarded as a safer alternative to conventional cigarettes. They are increasingly popular among adolescents of both sexes, and many smokers use e-cigarettes in their attempts to quit smoking. There is little understanding of the effects of exposure to e-cigarette vapors on human reproductive health, human development, or the functioning of the organs of the male and female reproductive systems. Data on the effects of the exposure were derived mainly from animal studies, and they show that e-cigarettes can affect fertility. Here, we review recent studies on the effects of exposure to e-cigarettes on facets of morphology and function in the male and female reproductive organs. E-cigarettes, even those which are nicotine-free, contain many harmful substances, including endocrine disruptors, which disturb hormonal balance and morphology and the function of the reproductive organs. E-cigarettes cannot be considered a completely healthy alternative to smoking. As is true for smoking, deleterious effects on the human reproductive system from vaping are likely, from the limited evidence to date.
Considering the topic and its importance, it's strange that this review only has 11 citations at this time. It has some 60+ references, but for simplicity, let's look at the male effects only. The claim about "studies show" testosterone reductions is true, ish. There is a such rat study. From Tunisia:
El Golli, N., Rahali, D., Jrad-Lamine, A., Dallagi, Y., Jallouli, M., Bdiri, Y., ... & El Fazaa, S. (2016). Impact of electronic-cigarette refill liquid on rat testis. Toxicology Mechanisms and Methods, 26(6), 417-424.
Electronic cigarettes (e-cigarettes) are becoming the fashionable alternative to decrease tobacco smoking, although their impact on health has not been fully assessed yet. The present study was designed to compare the impact of e-cigarette refill liquid (e-liquid) without nicotine to e-liquid with nicotine on rat testis. For this purpose, e-liquid with nicotine and e-liquid without nicotine (0.5 mg/kg of body weight) were administered to adult male Wistar rats via the intraperitoneally route during four weeks. Results showed that e-liquid with or without nicotine leads to diminished sperm density and viability, such as a decrease in testicular lactate dehydrogenase activity and testosterone level. Furthermore, quantitative real-time polymerase chain reaction (qRT-PCR) analysis identified a reduction in cytochrome P450 side-chain cleavage (P450 scc) and 17 beta-hydroxysteroid dehydrogenase (17βHSD) mRNA level, two key enzymes of steroidogenesis. Following e-liquid exposure, histopathological examination showed alterations in testis tissue marked by germ cells desquamation, disorganization of the tubular contents of testis and cell deposits in seminiferous tubules. Finally, analysis of oxidative stress status pointed an outbreak of antioxidant enzyme activities such as superoxide dismutase, catalase and gluthatione-S-transferase, as well as an important increase in sulfhydril group content. Taken together, these results indicate that e-liquid per se induces toxicity in Wistar rat testis, similar to e-liquid with nicotine, by disrupting oxidative balance and steroidogenesis.
Sounds scary! What are their methods:
A total of 24 rats were randomized into three groups of eight animals each as follows: Group 1: Control group was injected intraperitoneally with physiological saline (500 ml). Group 2: E-cigarette 0%-treated group received an intraperitoneal injection of electronic cigarette refill liquid without nicotine (less than 10 ml) diluted in physiological saline (500 ml). Group 3: E-cigarette-treated group received an intraperitoneal injection of electronic cigarette refill liquid containing 0.5 mg of nicotine/kg of bw/day (less than 10 ml) diluted in physio- logical saline (500 ml). Rats were treated for four weeks and sacrificed by decapitation 24 h after the last treatment.
Intraperitoneal.. what? Dictionary says "Within the peritoneal cavity (the area that contains the abdominal organs).". They literally injected rats with vaping liquid. Seems insane and incomparable to human vaping, but authors assure us it is legit:
The dose of e-liquid containing 0.5 mg of nicotine/kg of body weight (bw)/day and the intraperitoneally (i.p.) route were selected on the basis of a previously published report suggesting that daily i.p. administration of 0.5 mg of nicotine/kg of bw is a lower dose than a smoking comparable dose (Matta et al., 2007). Moreover, this dose did not show any sign of toxicity in rats (Higher doses caused paralysis of the back limbs of the animals, diarrheas and increased heart rate). Finally, i.p. route is still largely used to assess nicotine toxicity in rodents (Gerard et al., 2010; Gumustekin et al., 2005; Sener et al., 2005a,b, 2007; Zhang et al., 2015).
The results sure look halfway decent, maybe too good. Here's for sperm measures:
I found it strange that the sperm count is lower in the 0% nicotine group, but maybe this is just due to n=8 per group. Sperm viability shows a 60-70% decline. This kind of result seems crazy, but I would have said the same thing about saunas, perhaps, and look how strong that data is.
Here's the testosterone one that the Twitter people are on about:
So here we get it. There is a 50% reduction in one experimental group, the wrong one (0% nicotine), the other group looks like about 25% reduction.
The authors tell us that "Several studies on rodents have reported that nicotine affects sperm function by depressing sperm count and viability (Mosbah et al., 2015; Oyeyipo et al., 2011).", but they don't seem to realize that this is not fitting with their finding for the 0% nicotine group. If nicotine had an effect as they cite research to support, the nicotine group should be worse off than the 0% nicotine group.
The same author group then later in 2018 published a very similar paper based on the same rats and the same data (mostly) in a different journal with another lead author. I won't go into it here because it adds nothing.
Is there something more realistic? Yes, an Italian rat study with actual vapor:
Vivarelli, F., Canistro, D., Cirillo, S., Cardenia, V., Rodriguez-Estrada, M. T., & Paolini, M. (2019). Impairment of testicular function in electronic cigarette (e-cig, e-cigs) exposed rats under low-voltage and nicotine-free conditions. Life sciences, 228, 53-65.
Despite the lack of knowledge of the effects of electronic cigarettes (e-cigarettes, e-cigs) on public health, they have been proposed as a part of smoking cessation efforts. Recently, several basic scientific studies have pointed out how e-cigs can generate carcinogens, such as e-cig liquid thermal degradation by-products, and how the exposure can lead to genomic damage through inhibiting DNA repair or disrupting the redox homeostasis. However, scientific studies have pointed out how e-cigs can generate carcinogens and their release could be avoided setting the device to a low-voltage regimen. To test this feasibility, we show the effects of e-cig vapour generated from a low-voltage device filled with a nicotine-free liquid on rat testicular functions. The chemical analysis revealed the presence of carbonyls, such as formaldehyde, acetaldehyde and acrolein. Rats exposed reported a lower relative testis weight and higher levels of lactate dehydrogenase (LDH) as tissue damage marker, along with an impairment of 3β-hydroxysteroid dehydrogenase (3β-HSD), 17β-hydroxysteroid dehydrogenase (17β-HSD) and glucose-6-phosphate dehydrogenase (G6PDH) as key enzymes in the steroidogenesis pathway. The pro-oxidative environment was confirmed by the higher amount of reactive oxygen species (ROS), the development of lipid peroxidation and protein carbonylation, as well as from the disruption of antioxidant capability. Finally, we observed a higher rate of DNA unwinding in white blood cell line and boosted lipoxygenase (LOX)-linked activity, a tumour promotion marker. Even with the device setting at weak conditions, our results if extrapolated to humans suggest that exposure to e-cig vapours might alter gonads function in male vapers.
Their method:
Fourteen male Sprague-Dawley rats (7 weeks old) were purchased by ENVIGO RMS S.r.l. and housed under standard conditions (12-h light-dark cycle, 22 °C and 60% humidity). Animals had free access to water and chow throughout the experiment. After one-week acclimatization, animals were randomly assigned to the experimental units: control (7 rats) and exposed (7 rats). The exposed group was subjected to the vapour generated from the e-cigarette (see Section 2.2 for details on device settings) for 28 days. The exposure occurred daily for 3 h and it consisted of 11 cycles of two puff (6 s on; 5 s off; 6 s off), followed by 20 min of recovery. At the end of each cycle, the animals were moved to a clean chamber. The levels of O2 , N 2 and CO 2 were monitored by GC/MS to establish safe O 2/N 2 and CO 2/O 2 ratios. Further details on the exposure chamber assessment have been previously reported [5].
So 14 rats this time, 7 per group. Actual vapor, and quite a long time. They didn't measure testosterone, but they measures testicle sizes:
Both of these comparisons are p < .05, and not < .01, so the p values are bad. Another alternative, they measured some enzymes related to testosterone synthesis:
I don't know anything about the chemistry, but maybe some reader can tell us whether they buy this proxy. My hunch is that biology offers so many proxies that one can always find something that shows something somewhere and say its relevant based on some theory of pathway.
And there's a Polish study:
Wawryk-Gawda, E., Zarobkiewicz, M. K., Chłapek, K., Chylińska-Wrzos, P., & Jodłowska-Jędrych, B. (2019). Histological changes in the reproductive system of male rats exposed to cigarette smoke or electronic cigarette vapor. Toxicological & Environmental Chemistry, 101(7-8), 404-419.
The results appear to be all over the place and the paper is full of pictures of cells and stuff. I can't evaluate this.
Enough rats! Is there anything human? Yes:
A global survey showed that one out of eight smokers have attempted e-cigarettes, with most utilisation among young, non-minority individuals1 . Presently, there are no regulations on the use of these products. While detailed studies have been carried out looking at the effects of conventional smoking on sperm quality, no studies to date, have looked at the effects of e-cigarettes on male fertility. In this study, multiple methods have been utilised to distinguish whether e-liquid exposure affects testes function and sperm quality. The ejaculates from 30 men were investigated post gradient centrifugation. Semen samples were split into three groups and cultured with two popular e-liquid flavourings (bubblegum and cinnamon), which have been shown to have a cytotoxic effect on certain cell types2 , and propylene glycol (the base humectant found in all e-liquid solutions). Concentration, motility and progression were analysed and compared with control cultured sperm using Computer Assisted Sperm Analysis software. High concentrations of cinnamon and bubblegum were both statistically significant (P=<0.01) for reducing motility, progression and concentration. In order to assess the effect of e-cigarette inhalation on testes morphology in vivo, adult male C57/BL/6 mice were exposed to e-liquid flavor vapour for four weeks in air controlled cages before undergoing gonadectomy (n=3 for each exposure). The testes were sectioned, TUNEL stained and apoptosis measured using cell counts. Bubblegum flavouring yielded statistically significant results (P=<0.05) as the most damaging exposure causing apoptosis in mouse testes. This study highlights the need for further studies into the harmful effects of electronic cigarettes and provides evidence for the restriction of unregulated flavourings in e-liquids as well as the need for effective regulation internationally.
References:
1. Adkison, S.E., O’Connor, R.J., Bansal-Travers, M., Hyland, A., Borland, R., Yong, H.-H., Cummings, K.M., McNeill, A., Thrasher, J.F., Hammond, D., Fong, G.T. (2013) Electronic nicotine delivery systems: international tobacco control four- country survey. Am J Prev Med 44 (3): 207–215.
2. Bahl, V., Lin, S., Xu, N., Davis, B., Wang, Y., Talbot, P. (2012) Comparison of electronic cigarette refill fluid cytotoxicity using embryonic and adult models. Reprod. Toxicol. 34(4):529–537.
That's the entire study. I emailed first author to ask about any follow-up. She said that:
Hi Emil,
Thanks for reaching out. I gave this talk at the BFS and the Times reported it. Unfortunately I received a scary amount of abuse online from vapers and vaping companies who said very threatening things. I made the decision not to publish as a result but would be happy to send you ant data from this if I can find it.
Helen
Harassment campaigns work unfortunately.
So there's two parts of the study. One part where they "cultured" semen with vaping liquid, I think this means they mixed it in a petri dish. I mean, OK, this probably does something bad, but unclear what this would show about typical use. I don't suppose many people vape with their vaginas after sex. The second part is a n=9 mouse study that also exposed them to vaping gas and measured their testicles. Seems reasonable enough. They say this had an effect in one experimental group, p < .05. Who can say whether this was a fluke or not.
What about something more solid, and with humans? There's some media articles about vaping and men's fertility. CNN tells us Vaping doubled the risk of erectile dysfunction in men age 20 and older, study finds. They reference this study:
El-Shahawy, O., Shah, T., Obisesan, O. H., Durr, M., Stokes, A. C., Uddin, I., ... & Blaha, M. J. (2022). Association of e-cigarettes with erectile dysfunction: the Population Assessment of Tobacco and Health Study. American journal of preventive medicine, 62(1), 26-38. PDF
Methods
Data from Wave 4 (2016–2018) of the Population Assessment of Tobacco and Health study were analyzed in 2020. Male participants aged ≥20 years who responded to the erectile dysfunction question were included. Multivariable logistic regression models examined the association of ENDS use with erectile dysfunction within the full sample and in a restricted sample (adults aged 20–65 years with no previous cardiovascular disease diagnosis) while adjusting for multiple risk factors.
Results
The proportion of erectile dysfunction varied from 20.7% (full sample) to 10.2% (restricted sample). The prevalence of current ENDS [Electronic Nicotine Delivery Devices, i.e. e-cigarette] use within the full and restricted samples was 4.8% and 5.6%, respectively, with 2.1% and 2.5%, respectively, reporting daily use. Current daily ENDS users were more likely to report erectile dysfunction than never users in both the full (AOR=2.24, 95% CI=1.50, 3.34) and restricted (AOR=2.41, 95% CI=1.55, 3.74) samples. In the full sample, cardiovascular disease history (versus not present) and age ≥65 years (versus age 20–24 years) were associated with erectile dysfunction (AOR=1.39, 95% CI=1.10, 1.77; AOR= 17.4, 95% CI=12.15, 24.91), whereas physical activity was associated with lower odds of erectile dysfunction in both samples (AOR range=0.44−0.58).
Conclusions
The use of ENDS seems to be associated with erectile dysfunction independent of age, cardiovascular disease, and other risk factors. While ENDS remain under evaluation for harm reduction and smoking-cessation potential, ENDS users should be informed about the possible association between ENDS use and erectile dysfunction.
So it's a big observational study. Their results is one giant regression model:
Phew! Well, some things to look at. The column with OR are the bivariate relationships, i.e., association between erectile dysfunction (ED) and "EDNS" (vaping). So we see that without controls, vaping use is associated with less erectile dysfunction, about half the rate for former and current occasional smokers, p = .08 for daily smokers. I would guess these opposite of expected findings are due to age confounding. After the authors control for 20+ things, the association reverses, so that daily use of vaping is associated with ED with about twice the rate of normal (p <.001), but former and occasional use is not. But if you look later, they also have regular tobacco use which shows no association at all after controls! And neither does "other tobacco products", which means "past 30‒day use of cigar, cigarillos, pipe, hookah, snus, and smokeless tobacco products". This doesn't make any sense together with the various claims of some rat and mice researchers that nicotine itself does stuff. It appears vaping is magical.
Finally, I was able to find a Danish study of smoking and sperm counts:
Holmboe, S. A., Priskorn, L., Jensen, T. K., Skakkebaek, N. E., Andersson, A. M., & Jørgensen, N. (2020). Use of e-cigarettes associated with lower sperm counts in a cross-sectional study of young men from the general population. Human Reproduction, 35(7), 1693-1701.
STUDY DESIGN, SIZE, DURATION
This cross-sectional population-based study included 2008 men with information on cigarette and marijuana use (enrolled between 2012 and 2018), among whom 1221 men also had information on e-cigarette and snuff use (enrolled between 2015 and 2018).
PARTICIPANTS/MATERIALS, SETTING, METHODS
Men (median age 19.0 years) from the general population provided a semen and blood sample and filled out a questionnaire on lifestyle including information on smoking behaviour. Associations between different types of smoking (e-cigarettes, snuff, marijuana and cigarettes) and reproductive hormones (total and free testosterone, sex hormone-binding globulin, LH, oestradiol and ratios of inhibin B/FSH, testosterone/LH and free testosterone/LH) and semen parameters (total sperm count and sperm concentration) were examined using multiple linear regression analyses adjusted for relevant confounders.
MAIN RESULTS AND THE ROLE OF CHANCE
Approximately half of the men (52%) were cigarette smokers, 13% used e-cigarettes, 25% used snuff and 33% used marijuana. Users of e-cigarettes and marijuana were often also cigarette smokers. Compared to non-users, daily e-cigarette users had significantly lower total sperm count (147 million vs 91 million) as did daily cigarette smokers (139 million vs 103 million), in adjusted analyses. Furthermore, significantly higher total and free testosterone levels were seen in cigarette smoking men (6.2% and 4.1% higher total testosterone and 6.2% and 6.2% higher free testosterone in daily smokers and occasional smokers, respectively, compared to non-smoking men), but not among e-cigarette users. Daily users of marijuana had 8.3% higher total testosterone levels compared to non-users. No associations were observed for snuff in relation to markers of testicular function.
LIMITATIONS, REASONS FOR CAUTION
We cannot exclude that our results can be influenced by residual confounding by behavioural factors not adjusted for. The number of daily e-cigarette users was limited and findings should be replicated in other studies.
It's a study of 2000 Danish men aged 19, who took part due to serving in the army. Of this sample, there were some who used various kinds of nicotine, 25 daily vapers and another 139 occasional vapers. So the authors were able to produce these neat plots. First, testosterone:
So regular smokers had somewhat higher testosterone levels than non-smokers (p < .01), again contradicting the animal researchers' results (some of them). Cannabis showed the same pattern (but p = .05). Vaping didn't show any associations, but with only 25 daily smokers, it can't be ruled out either, but the effects cannot be large like those seen in the rat studies. Snuff didn't seem to show any association either.
Results for sperm:
Sperm counts were a bit lower for the smokers (p < .01), vapers (p = .01), and not much pattern for the last two groups. It doesn't appear that vapers are worse than regular smoking wrt. sperm, but this study wasn't large enough to say for certain. Also, we aren't that certain that smoking and sperm counts are causal.
Conclusions
I wouldn't put much trust in the Tunisian rat study, or most other such animal studies.
Strange association between erectile dysfunction and vaping, that somehow doesn't show up for other kinds of nicotine products. Not concerning enough to stop using though IMO.
Testosterone associations seem to be positive in actual humans from observational data. It seems easy to do a randomized trial here. Get 200 men, start a random half of them on vaping daily for 3 weeks. Measure all the usual things every week.
Sperm count showed about the same negative association with regular smoking as with vaping, so there doesn't seem to be any particular additional course for concern. As we saw with the heat, these counts are easily reversible.
All in all, not much cause for concern, but considering the prevalence of the practice, it should be immediately properly investigated (large RCTs, pre-registration, open data, multiple teams).