Mobile phones affect multiple sperm quality traits: a meta-analysis

As mobile phone usage is growing rapidly, there is a need for a comprehensive analysis of the literature to inform scientific debates about the adverse effects of mobile phone radiation on sperm quality traits. Therefore, we conducted a meta-analysis of the eligible published research studies on human males of reproductive age. Eleven studies were eligible for this analysis. Based on the meta-analysis, mobile phone use was significantly associated with deterioration in semen quality (Hedges’s g = -0.547; 95% CI: -0.713, -0.382; p < 0.001). The traits particularly affected adversely were sperm concentration, sperm morphology, sperm motility, proportion of non-progressive motile sperm (%), proportion of slow progressive motile sperm (%), and sperm viability. Direct exposure of spermatozoa to mobile phone radiation with in vitro study designs also significantly deteriorated the sperm quality (Hedges’s g = -2.233; 95% CI: -2.758, -1.708; p < 0.001), by reducing straight line velocity, fast progressive motility, Hypo-osmotic swelling (HOS) test score, major axis (µm), minor axis (µm), total sperm motility, perimeter (µm), area (µm 2), average path velocity, curvilinear velocity, motile spermatozoa, and acrosome reacted spermatozoa (%). The strength of evidence for the different outcomes varied from very low to very high. The analysis shows that mobile phone use is possibly associated with a number of deleterious effects on the spermatozoa.


Introduction
Almost 10% of men of reproductive age are estimated to be subfertile 1 . Owing to its complexity, even after identification of a plethora of underlying factors, etiology in almost half of the infertile subjects tested at fertility clinics remains obscure 2 . Hence, the list of the causes of male infertility is growing by the day with recent advances in fertility research 3 . Though advances in assisted reproduction technologies (ARTs), especially in the form of in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI), have helped subfertile couples conceive offspring, it is feared that ARTs only bypasses the problem of subfertility and contributes towards hiding the underlying causes which have at times led to serious health problems in offspring 4,5 . Hence, identification of unknown aetiologies would help in prescription of specific preventive measures that will ultimately decrease the incidence of male infertility.
Most nations, especially developing countries, are witnessing an increase in the use of various radiation-emitting domestic-purpose devices that could cause mild to serious health problems based on the duration and intensity of usage 6 , and reduced fertility is now recognised as one such problem 7 . Wireless mobile phones are one of the most accepted devices with a tremendous increase in usage across the world in recent times 8 . Research into the impact of ionizing radiation on the development of various types of health disorders, especially cancers, has been well established 9 . Similarly, several studies have found an increase in the risk of developing some types of tumors after long-term exposure to non-ionizing radiation from mobile phones 10 . Research into the effects of mobile phone radiation on male fertility, though growing, is limited and inconclusive 11,12 . Recently, several case-control studies have reported results from a general population setting alongside a few studies from subfertile populations 7,13-20 . Like ionizing radiation, non-ionizing radiation is also expected to affect spermatozoa, though in subtle ways 21 . The aim of this meta-analysis was, therefore, to investigate the impact of mobile phone radia in vitro as well as in vivo settings in men of reproductive age from both general and subfertile populations.

Material and methods
A systematic search of an electronic database was conducted to retrieve published studies on the impact of mobile phone radiation on semen parameters in adult men. The results have been reported according to the standards of the guidelines for meta-analysis of observational studies in epidemiology 22 . All English language research studies published up until January 2012 in scientific journals indexed in the searched databases were included for analysis.

Inclusion/exclusion criteria and outcomes of interest:
The studies on human males of reproductive age reporting the effect of mobile phone radiation on any or all measures of semen volume, total sperm count, sperm concentration, sperm motility or sperm morphology were included. All the studies that did not satisfy the inclusion criteria were excluded.
Search strategy, data extraction and meta-analysis: Google Scholar and NLM's PubMed database were searched for articles by using different combinations of 4 mobile phone related keywords ['mobile phone', 'cellular phone', 'radiofrequency electromagnetic waves (RF-EMW)', 'radiation'] with 5 sperm quality related keywords ('spermatozoa', 'semen', 'sperm concentration', 'sperm motility', 'sperm morphology') Data from 11 eligible studies were extracted and separated into in vitro and in vivo categories.
Effect sizes were expressed as Hedges's g 23 , separately for in vivo & in vitro studies using individual semen parameters as units of analysis (Supplementary Table 1). A random model was used to test and quantify effect size using 'Comprehensive Meta-Analysis (v.2)' trial version 24 . A random effect model was preferred over a fixed effect model in order to account for differences in both effect size and sampling error 25 .

Results
In vivo effects of mobile phone radiation Our analysis shows that overall, mobile phone users had significant deterioration in semen quality (Hedges's g = -0.547; 95% CI: -0.713, -0.382; p < 0.001). There was significant heterogeneity among effect sizes (Q = 475.985, p < 0.001), which suggest that some of the semen parameters may not be affected by mobile phone exposure. Hence, combined effect-size for each of the semen parameters were calculated separately (Table 1), and it was found that sperm concentration, sperm morphology, sperm motility, proportion of non-progressive motile sperm (%), proportion of slow progressive motile sperm (%), and sperm viability were deteriorated in individuals exposed to mobile phone radiation. By contrast, semen volume, liquefaction time, semen pH, proportion of rapid progressive motile sperm (%), and semen viscosity were not affected by mobile phone usage.
Publication bias could potentially change the results of metaanalysis but analysis of funnel plot of precision by Hedges's g using Dual and Tweedie's trim-and-fill test 26 did not change the overall effect size, suggesting little bias. Moreover, Rosenthal's fail-safe N test 27 revealed that 3964 missing studies with a mean Hedges's g of 0 are required for the combined 2-tailed p-value to exceed 0.050. In other words, there need to be 99.1 missing studies for every observed study for the effect to be nullified.
In vitro effects of mobile phone radiation Experimental exposure of spermatozoa isolated from healthy men of reproductive age to mobile phone radiation significantly affected sperm quality (Hedges's g = -2.233; 95% CI: -2.758, -1.708; p < 0.001). There was significant heterogeneity among effect sizes (Q = 639.294, p < 0.001), suggesting that similar to in vivo exposure, in vitro exposure may also not affect all the parameters of spermatozoa. Hence, combined effect-size for spermatozoa parameters were calculated separately (Table 1), and it was found that exposure to mobile phones significantly reduced straight line velocity, fast progressive motility, Hypo-osmotic swelling (HOS) test score, major axis (µm), minor axis (µm), total sperm motility, perimeter (µm), area (µm 2 ), average path velocity, curvilinear velocity, motile spermatozoa, and acrosome reacted spermatozoa (%). By contrast, DNA fragmentation levels, non-progressive motility, total antioxidant capacity (TAC), progressive motility, reactive oxygen species (ROS) generation, slow progressive motility, sperm concentration, and sperm zona binding was not affected by mobile phone radiation.
A Funnel plot of precision by Hedges's g using Dual and Tweedie's trim-and-fill test did not change the overall effect size, suggesting little publication bias. Rosenthal's fail-safe N test revealed that 3813 missing studies with a mean Hedges's g of 0 are required for the combined 2-tailed p-value to exceed 0.050. In other words, there need to be 100.3 missing studies for every observed study for the effect to be nullified.

Discussion
This study was aimed to analyse the data assessing the risk of mobile phone radiation on male fertility. Our results suggest that mobile phone radiation has a tendency to significantly affect sperm quality. Based on the design of the analysed records, we divided studies into in vivo studies and in vitro studies. The effect size was significant in both the categories, suggesting that mobile phone radiation could severely compromise male fertility. This conclusion is robust, as a fail-safe test suggested that the results are not likely to be mediated by publication bias.
The number of worldwide mobile subscriptions grew from less than 1 billion in 2000 to over 6 billion in 2012 8 , with more than half of these subscribers estimated to be children and young adults. Hence, it is very likely that in the coming decades, we could witness an increase in the incidence of male infertility due to mobile phone radiation exposure, similar to growing concerns over other hazards.
Although the mechanism of cell phone radiation-mediated health defects is still obscure, it is proposed that their ability to produce heat, disrupt cell membranes, affect endothelial function, alter the blood-brain barrier, and modulate neuronal excitability have the potential to affect multiple physiological functions simultaneously 28-30 . To our knowledge, this is the first meta-analysis of the effects of mobile phone radiations on various sperm quality parameters. Cellular phones have become integral part of everyday life, and newer versions of these are developed very rapidly these days. Hence, it is necessary to educate the users about the hazards of cell phones as well as test the newer versions like smartphones for health hazards.

Competing interests
No relevant competing interests were disclosed.

Grant information
The author(s) declared that no grants were involved in supporting this work. On the surface, the results seem quite striking with virtually any sperm endpoint one can imagine being significantly altered in the collective analysis of mobile phone studies compiled. However, upon looking at the data in the supplementary table, it is obvious that the relatively few studies compiled varied widely both in respect to endpoints measured and the sample size. As shown in Table 1, motility is the endpoint representing the greatest combined sample size for both and studies. Motility in vivo in vitro was measured in 4 out of 4 studies and 5 out of 7 studies. So motility 'might' be an in vivo in vitro endpoint that is repeatedly altered by cell phone exposure. The reason for 'might' is the lack of any reported exposure data in this study. In summary, the small sample size and lack of exposure data significantly weaken the conclusions of this study.

Supplementary
I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.
No competing interests were disclosed. We have studied the reviewer comments and would like to justify our results. Our analysis is