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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.
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.