Saadat1 wrote that there has only been one study on the association between human offspring sex ratio (proportion male) at birth and parental exposure to electromagnetic fields (EMF). He substantiated this claim with a reference to Irgens et al.2 However, I3 cited six other such studies.4–9 These studies, although not unanimous, cumulatively suggest that both exposed men and exposed women tend to produce significant excesses of daughters. This suggestion is not much changed by the comparatively small samples adduced by Saadat.1 The point may be illustrated by considerations of standard power analysis.10 Suppose that you wished to test that exposure has the effect of reducing the offspring sex ratio by, say, 10% (viz from an expected value of 0.515 to 0.465). Then, to stand 8 chances in 10 of detecting a difference at the 0.05 level (one way), you would require equal sized samples (of offspring of exposed and non-exposed subjects) each numbering 1236. The number of offspring of Saadat’s1 sample of exposed subjects was 110.
In my letter I cited3 evidence that exposure of men to EMF is associated with fatigue, headaches, dizziness, impaired memory, nausea, loss of strength in limbs, respiratory difficulties, sleep disturbances, and reduced libido. Such reports may be dismissed as subjective. However I also cited reports that exposure to EMF was associated with reduced sperm counts in men and rats: and of reduced testosterone levels in rats. And more recently, men’s exposure to radiofrequency radiation has reportedly been linked to a lowered testosterone/gonadotrophin ratio.11 And there are good grounds for suspecting this hormone profile to be causally associated with low offspring sex ratios.12,13 More data are urgently needed on the sexes of offspring of men and women who have been exposed to EMF.
References
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Saadat M. Offspring sex ratio in men exposed to electromagnetic fields. J Epidemiol Community Health2005;59:339.
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Irgens A, Kruger K, Skorve AH, et al. Male proportion in offspring of parents exposed to strong static and extremely low frequency electromagnetic fields in Norway. Am J Ind Med 1997;32:557–61.
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James WH. The sex ratios of offspring of people exposed to non-ionising radiation. Occup Env Med1997;54:622–3.
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Nordstrom S, Birke E, Gustavsson L. Reproductive hazards among workers at high voltage substations. Bioelectromagnetics1983;4:91–101.
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Knave B, Gamberale F, Birke E, et al. Long term exposure to electric fields: a cross-sectional epidemiologic investigation of occupationally exposed workers in high voltage substations. Scand J Work Environ Health 1979;5:115–25.
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Mubarak AAS, Mubarak AAS. Does high voltage electricity have an effect on the sex distribution of offspring? Hum Reprod1996;11:230–1.
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Larsen AI, Olsen J, Svane O. Gender specific reproductive outcomes and exposure to high frequency electromagnetic radiation among physiotherapists. Scand J Work Environ Health1991;17:324–9.
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Guberan E, Campana A, Faval P, et al. Gender ratio of offspring and exposure to shortwave radiation among female physiotherapists. Scand J Work Environ Health 1994;20:345–8.
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Kolodynski AA, Kolodynska VV. Motor and psychological functions of school children living in the area of the Skrunda radiolocation station in Latvia. Sci Total Environ1996;180:87–93.
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Snedecor GW, Cochran WG. Statistical methods. 6th ed. Ames, IA: Iowa State University Press, 1967:222.
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Grajewski B, Cox C, Schrader SM, et al. Semen quality and hormone levels among radiofrequency heater operators. J Occup Environ Med 2000;42:993–1005.
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James WH. Evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels at the time of conception. J Theor Biol1996;180:271–86.
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James WH. Further evidence that mammalian sex ratios at birth are partially controlled by parental hormone levels around the time of conception. Hum Reprod2004;19:1250–6.
Author’s reply
I thank Dr James for his letter. He may well be correct for the citations of the related studies and also the estimation of the sample size. However, I wish to make some comments.
Not only in my report,1 but also in other reports2–4 the sample size was much lower than that estimated by James. Among published data, the article of Guberan et al5 was based on 1781 births (508 and 1273 births from exposed and unexposed pregnancies, respectively), which is a comparatively large sample size and it is near to the required sample size, calculated by James. Guberan et al found that there was no statistically significant difference between exposed and unexposed pregnancies for offspring sex ratio.5 Irgens et al reported that offspring sex ratio of women in industries with electromagnetic fields was significantly reduced; while in men exposed to the fields the ratio did not show significant difference.6 On the other hand, experimental design studies showed that when rodents (mice and rats) were exposed to electromagnetic fields, the offspring sex ratio significantly increased7 or remained unchanged,8,9 compared with their controls. Taken together it seems that the published data are not sufficient to conclude that the offspring sex ratio tends to produce significant excesses of daughters when parents are exposed to electromagnetic fields.
References
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Saadat M. Offspring sex ratio in men exposed to electromagnetic fields. J Epidemiol Community Health2005;59:339.
- ↵
Nordstrom S, Birke E, Gustavsson L. Reproductive hazards among workers at high voltage substations. Bioelectromagnetics1983;4:91–101.
-
Knave B, Gamberale F, Bergstrom S, et al. Long-term exposure to electric fields. A cross-sectional epidemiologic investigation of occupationally exposed workers in high voltage substations. Scand J Work Environ Health 1979;5:115–25.
- ↵
Larsen AI, Olsen J, Svane O. Gender-specific reproductive outcomes and exposure to high-frequency electromagnetic radiation among physiotherapists. Scand J Work Environ Health1991;17:324–9.
- ↵
Guberan E, Campana A, Faval P, et al. Gender ratio of offspring and exposure to shortwave radiation among female physiotherapists. Scand J Work Environ Health 1994;20:345–8.
- ↵
Irgens A, Kruger K, Skorve AH, et al. Male proportion in offspring of parents exposed to strong static and extremely low-frequency electromagnetic fields in Norway. Am J Ind Med 1997;32:557–61.
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Wang SM, Wang DW, Peng RY, et al. Effect of electromagnetic pulse irradiation on mice reproduction. Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi 2003;21:329–31.
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Ohnishi Y, Mizuno F, Sato T, et al. Effects of power frequency alternating magnetic fields on reproduction and pre-natal development of mice. J Toxicol Sci 2002;27:131–8.
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Ryan BM, Symanski RR, Pomeranz LE, et al. Multigeneration reproductive toxicity assessment of 60-Hz magnetic fields using a continuous breeding protocol in rats. Teratology 1999;59:156–62.
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