The tl;dr: maybe a little but for benign reasons. If fertility is important to you and you are a man, don’t put hot things in your pockets. This may fall into the category of switching from tidy whities to boxer briefs.
A study came out in September suggesting that it does. It is a meta-analysis by Jessica Adams et all, published in Environmental International, called “Effect of mobile telephones on sperm quality: A systematic review and meta-analysis.”
The study considered the effects of radio-frequency electromagnetic radiation (RF-EMR) on sperm motility (movement), viability, and concentration. As a meta-analysis, the study looked at several in vitro and in vivo analyses, combining the results, and using a statistical analysis to test the idea that RF-EMR has an effect on any one of these three variables. In total, ten studies were selected from a wider range of studies (the others were eliminated for various reasons) across which a total of 1492 sperm specimens were analyzed. The results, from the abstract:
Exposure to mobile phones was associated with reduced sperm motility (mean difference ? 8.1% (95% CI ? 13.1, ? 3.2)) and viability (mean difference ? 9.1% (95% CI ? 18.4, 0.2)), but the effects on concentration were more equivocal. The results were consistent across experimental in vitro and observational in vivo studies. We conclude that pooled results from in vitro and in vivo studies suggest that mobile phone exposure negatively affects sperm quality. Further study is required to determine the full clinical implications for both sub-fertile men and the general population.
Not all studies looked at all effects and there were other differences between them. See the original study (link above) to find all the details.
Of the nine studies that looked at motility, six indicated a reduction due to mobile phones. Five of the studies looked at viability, with four of the five indicating a negative effect. Six studies addressed concentration but with very inconsistent results.
An effect means little unless there is an explanation that makes sense. Several different ways in which RF-EMR could affect sperm are considered in this meta-analysis.
One possible cause is production of reactive oxygen species (ROS) which could lead to DNA damage. ROS are molecules including Oxygen that happen in the normal day to day course of biological activity in cells but that can increase in frequency for a number of reasons, including, and most famously, ionizing radiation. Oxygen is a highly reactive element. When life first arose on earth, Oxygen was not commonly available and was generally destructive to the finely tuned molecular processes associated with living form (probably, and I oversimplify). But life processes tended to release oxygen from molecules in which it was more or less safely sequestered. By and by life processes evolved that handled oxygen by re-sequestering it, life processes evolved that made use of the highly reactive nature of oxygen.
An analogy for this is Xander Cage (Vin Diesel) in the movie xXx. Cage is a dangerous out of control tough guy who has capabilities that the government (represented by Agent Augustus Eugene Gibbons, played by Samuel Jackson) requires for an important task. Cage is tamed, in a sense, so he can carry out the government’s bidding, but at the same time he remains dangerous. There are many movies with this theme. Imprisoned highly capable and dangerous bad guys are given a chance to play a useful role; they are needed because of there capabilities, but their capabilities are dangerous ones, so their exploitation comes with a risk. The exploitation of one of nature’s most dangerous elements, oxygen, provides life with some incredible capabilities, but as a risk.
Oxygen is usefully employed by nature. Oxygen damages biological processes. Nature employs counter measures to minimize that danger (i.e., “anti-oxidants”). But sometimes those counter measures are not enough, either because a very rare form of ROS comes along, one that is not accounted for by life’s counter-measures, or because a counter-measure is simply overwhelmed (or otherwise interfered with).
So in this scenario, RF-EMF cause the generation of a greater quantity of ROS, or especially damaging ROS. My understanding is that this is generally considered unlikely because the range of RF-EMF produced by cell phones is thought to not be physically capable of influencing ROS quality or quantity. However, the authors of this study argue that it is possible:
A small amount of ROS has an important functional role in sperm capacitation, the acrosome reaction, and binding to the oocyte (Garrido et al., 2004). Experimental disruption of the flow of electrons through the mitochondrial electron transport chain has been shown to increase ROS production significantly, with negative consequences for sperm motility (Koppers et al., 2008). In vitro evidence found EMR emitted at the same frequency as mobile phones increased mitochondrial ROS production and DNA fragmentation in sperm, and decreased motility and viability ( De Iuliis et al., 2009). The trends seen in this meta-analysis are consistent with these effects.
A second kind of effect is thermal. Sperm normally develop, in humans (and perhaps mammals in general) in a narrow range of temperatures. Increasing temperatures could interfere with this. There are two ways in which temperature increases could occur. One is that the RF-EMF excites molecules at the site of spermatogenesis, increasing temperatures. RF-EMF in the range emitted by cell phones can certainly do this if there is enough energy. This is what a micro-wave oven is. This particular thermal effect is minimal with cell phones. Were it not minimal we would be slowly cooking our hands and faces while we talked on the phone. Still, at least one study cited by Adams et all shows an increase in heat of people’s faces while they are taking on a cell phone. It is possible that a very small effect that normally has no biological significance would affect sperm production because it is sensitive to heat changes. This effect is considered to be very unlikely as it is simply too small.
However, cell phones also become warm, and this heat could be transmitted to the site of spermatogenesis. I learned about hot cell phones shortly after getting my first smart phone. I had left some apps running (I think the camera app was the culprit) and blanked the screen. The phone sat in my pocket for a while and I noticed a very uncomfortable sensation of increased heat. When I took the phone out of my pocket it was quite hot. It is possible that this made my sperm unhappy.
This study has some severe limitations, some of which are discussed by the authros.
Heterogeneity, that is variation between studies that is greater than expected due to sampling error … is an issue in most meta-analyses. Heterogeneity was high in all our meta-analyses (I2 > 88%) … However, our meta-analysis did include nearly 1500 samples, which increases confidence in the results. The heterogeneity in the motility meta-analysis was partially due to the differences in mobile phone exposure times, as the subgroup analyses demonstrated. The high heterogeneity and relatively low number of studies also precluded meaningful assessment of publication bias… However, sensitivity analyses demonstrated minimal differences when individual studies were excluded, with a tendency for our results to be conservative.
The possibility of confounding variables influencing the results of the observational studies cannot be ruled out. For example, participant age and smoking status were not consistently reported, so it is possible that these affected the observational studies since they are known to affect some semen quality parameters … [S]tudy populations taken from fertility clinics, as used in many studies on male fertility, may not be representative of the general population, as they are likely to contain a higher proportion of men with sperm parameters outside the WHO reference range.
Again, see the original study for more detailed discussion of these limitations.
It is possible that studies that fail to show an effect are simply unpublished and if available would balance out the meta-analysis. The degree of effect is small, so if there was random variation in outcome and several studies on one side of the mean outcome are removed, a small effect would be expected. There may be something about men who keep their cell phones in their pockets that relates to infertility. That seems like a strange idea, but if, for example, thermal effects are important, simply keeping numerous objects in one’s pockets could affect air flow and heat distribution in and near the nether regions. There is no control here; there is not a study of men who keep objects that are identical to cell phones but electronically inert (placebo-phones, if you will) in their pockets. Perhaps men who keep their cell phones on belt clips represent the higher-sperm production men while those who keep their cell phones hidden away have lower sperm production. A control study that looks at external cell phone attachment devices, and probably pocket protectors and other paraphernalia, in relation to fertility and overall manliness would be … well, probably not fundable so forget it.
The important outcome of this study, I think, is that a careful look via many studies of the effects of cell phones on a biological process known to be rather delicate (the making of sperm) shows only a minor effect at best, with much equivocation on whether there is an effect at all. Furthermore, the most likely effect is simply heat, having an object in your pocket that generates extra heat in a region where evolution had previously designed a cooling mechanism, a dangling scrotum that normally keeps the external testes away from the body.
There is the possibility that if anything is happening here at all, it would effect sperm quality in other ways, including DNA or chromosomal damage. That would be important to know. Female egg production is very different from male sperm production, so the two cases are not very analogous, but if there is an effect on sperm it might be worth asking if there is an effect on age. If the effect is anything other than heat, i.e., if it has to do with RF-EMR affecting molecules in cells, then something very important may be going on other than a small effect on fertility. Affecting molecular activity with radio waves might be a thing, and an area of future research and the possible development of medical diagnosis or even treatment. Most of the claims of radio waves for therapy or treatment, however, are wooish bunk. It seems that more study is merited, but for interesting academic reasons and not because this is a clear and present danger.