A series of recent publications discussed an increase in the male to female (M/F) ratio at birth supposedly under the impact of radiation from nuclear tests and accidents. However, social factors have not been sufficiently analyzed. Additional doses due to the radioactive contamination have usually been negligible compared to the natural background radiation. Bias is not excluded in epidemiological studies of low-dose radiation: surveillance and recall bias, dose-dependent selection and self-selection. Among others, ideological bias is aimed at a strangulation of nuclear energy production. One of the main causes of the elevation of M/F ratio at birth in certain regions is the son preference and sex-selective abortions after a prenatal ultrasonic gender testing. Migrations contribute to a global M/F shift. A relatively high M/F ratio prior to the introduction of the ultrasonic testing is an indication to other perinatal sex selection methods e.g. female neonaticide and abandonment of newborn girls. Besides, reduced M/F ratio has been associated with an older age at childbearing. In conclusion, the hypothesis that anthropogenic elevation of the radiation background contributed to the skewing of M/F ratio toward males is unproven. Dose-response relationships at low radiation doses should be studied in large-scale animal experiments applying dose rates comparable to those in humans.
Key words: Ionizing radiation; Dose rate; Chernobyl; Fukushima Daiichi accident; Male to female ratio at birth
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