Changes in the ratio of baby girls to boys born to millions have been linked to a variety of pollutants and indicators that poverty.
A study of half of the US population and all of Sweden found that more boys were born due to mercury, chromium, and aluminium pollution. However, lead pollution led to an increase in the number of girls being born. High chemical exposures may have also contributed to a lower sex ratio due to the close proximity of farming.
Deprivation measures, such a high number fast food restaurants or vacant buildings, were also associated with statistically significant increases in sex ratios.
However, correlations between other factors like the season of birth and weather temperature, as well as rates of violent crime or unemployment, were not significant.
The research only shows correlations between the various factors at birth and sex ratios, and not cause and effect. The researchers stated that future research would be required to determine causal links between the chemicals and human cells, as well as animal models in the laboratory.
This is a list of suspected suspects that we will investigate. However, all of the suspects have some credible evidence but are still far from conviction, according to Andrey Rizhetsky of the University of Chicago who conducted the research.
At conception, the sex of babies will be determined. This means that half of embryos should have to be females and half should have to be boys. However, hormonal factors can result in skewed sex ratios. For example, more male embryos may be terminated during pregnancy than more female embryos.
Rzhetsky stated that the question is how, and there are many factors to consider, including stress or changes in the environment. It makes sense that it can change because the physiology and biology of male and feminine embryos are different. They come from different hormonal backgrounds.
There are many myths surrounding sex ratios and birth. However, when you do some research, it turns out that most of the data that was tested on real data was only tested on very small samples. [risking spurious correlations]He said that some statements are not supported by observations.
The new research Published in the journal Plos Computational BiologyThis is the first study of chemical pollutants and other environmental factors that used large datasets from both continents. It used data from 150 million Americans over eight years and data from 9 million Swedish citizens over 30 years.
The factors that led to significant changes in sex ratios, such as mercury pollution or proximity to industrial plants, saw them shift by as much as 3%. For a population of 1,000,000, this would mean that there are 60,000 more boys than girls, or vice versa. The impact of PCBs on sex ratios was not studied in the past. However, the new analysis showed that it had a significant effect on the number of boys.
The researchers also looked at two extremely stressful events in the US, Hurricane Katrina in 2005 as well as the Virginia Tech shootings of 2007. The researchers only found a significant shift in the sex ratio after the Virginia Tech shootings. There was also more girls born. Rzhetsky stated that studies should focus on the most affected people, not whole populations, to investigate this further.
The study was able to draw strong statistical power from the large sample sizes. However, scientists also noted that they did not have data about the sex of stillborn infants and that all the US populations were covered by private medical insurance. Therefore, the results may not be representative of the entire population.
Gareth Nye (UK, University of Chester) is an expert in pregnancy and was not part of the study team. He said: The idea is that pollutants might influence the very early stages of fertilisation, leading one sex direction to the other. [But]These associations will always exist without cell research.
He stated that it is clear that pollutants play a part in the development of disease and health. This form of computational research helps us to understand why. He said that while the populations were large, the US births were relatively small with the total over 8 year less than the annual average 3.8m births. This does not necessarily mean that there aren’t other factors. [the study is]Although the quality is lower, it does not necessarily mean that the conclusions are less certain.