People are giving birth to less and less. This cannot be denied: this decline in fertility rates occurs in low-, middle-, and high-income countries and has persisted since the 1970s.
The big question is why. To what extent are fertility declines the result of social changes, economic conditions, and cultural changes that make childbearing less desirable or practical? As countries get richer and women get educated, the birth rate goes down a lot, so obviously that’s a big part of it.
But what about the decline in our biological ability to have children? Has something changed in the environment that – to use the scientific term for this biological ability – makes us less fertile?
A new study appears to have provided the answer. He focused on a class of chemicals known as PFAS, short for per- and polyfluoroalkyl substances. They are used in a variety of consumer products such as non-stick pans, waterproof clothing, and food packaging. These chemicals are found in most people’s bodies, and because they take so long to break down, they have earned the intimidating name “Forever Chemicals.”
PFAS has been cited as a possible cause of impaired fertility and fertility along with other chemicals, possibly because they can disrupt hormones or possibly cause diseases that make it difficult to conceive (however, none of the evidence listed here is conclusive). . ).
Some evidence comes from animal studies: studies have shown that exposure to chemicals in rats and mice has a negative effect on reproductive function. The problem – apart from the inherent problem of comparing non-human animals to human animals – is that the concentrations of chemicals in animal experiments are usually much, much higher than in real people. As with all “poisons”, a dose does the trick: something harmful in high concentrations can be perfectly harmless if the average person never has it in their system in large quantities.
Defender — which has published dozens of papers on these “dangerous,” “potentially toxic” chemicals over the past few years — called the new study “the first known study of the effects of PFAS on female fertility.” This is a little strange, given that earlier this year a review study pooled 13 previous similar studies and concluded that “increased exposure to PFAS is associated with reduced fertility in women.”
As with all such reviews, this conclusion depends on the quality and consistency of the main 13 studies. Unfortunately, the studies we have are all over the place: while on average they suggest an association between PFAS and lower fertility, estimates of the magnitude of the association vary greatly from study to study.
This is probably due to the fact that the studies looked at women in different countries, at different ages, at different times of pregnancy, and even measured PFAS in the blood in different ways. The review authors wrote that these issues “limit the validity of the evidence.”
There were other difficulties in the testimony. A 2018 Danish study, for example, came to the surprising conclusion that the concentration of PFAS in the blood of a pregnant woman was associated with her fertility if she already had children, but not if it was her first child. It’s not clear why this happens – do the chemicals take longer to build up in the body? Some unexpected statistical artifact? – but this was confirmed in a review study, one of the findings of which was that there was no evidence of an association between these chemicals and first pregnancy characteristics.
Thus, it is clear that there are many unanswered questions about the relationship between PFAS and female fertility. Therefore, additional evidence is welcome. The new study looked at a sample of 382 women in Singapore, all of whom were trying to conceive. They used a blood test to check the levels of different types of PFAS in the women’s blood and tracked them over the course of a year to see who got pregnant and who didn’t. After that, they found that 332 women were pregnant and 50 were not. Were there differences in blood levels of PFA between the two groups?
This is where things get tricky even before we get to the blood samples. Not only did the groups differ in pregnancy status, there were also very large differences in education between the groups.
71 percent of pregnant women had higher education; only 44 percent of non-pregnant women did so (interestingly, this is the opposite of what one would expect from the global trends mentioned above, but keep in mind that this is only a small sample within one country, so it is not representative).
Such a large difference in education levels meant that the groups were not completely comparable: on average, they likely lived very different lives, which could have had a lot to do with their fertility. In a randomized trial, the “randomized” portion would mean that these factors would not differ between groups, but this was (understandably given that this was a toxicity study) an observational study, so no randomization was performed.
It is true that the researchers “adjusted” their analysis for education, meaning they included education in their statistical model to try to ask the question, “If everyone had the same level of education, what would these outcomes be?” different? “? But statisticians point out that adjusting is much more difficult than many scientists think. The question arises: if the groups differed so much in education, how much could they differ in other potentially important factors that the researchers did not measure?
Then we come to the results. The researchers measured three different outcomes: whether the woman became pregnant; time to conception (longer time indicates lower fertility); and if she was born alive. They analyzed them using blood levels of seven different types of PFAS and a “blend” of different PFAS.
There are 24 different analyzes in total, more in the appendix to the article. Because the authors did not pre-register their study design, we do not know if they performed further analysis but did not publish it.
They found that two or three of these multiple analyzes were statistically significant, indicating that blood levels of PFAS correlated with greater difficulty conceiving. But the more tests you do, the more likely you are to find a false positive. The results aren’t particularly strong, and it’s entirely possible (sorry for the pun, given the topic here) that they are simply the result of normal statistical fluctuations, and not something “real” going on in the data.
This is the type of study that, with a more rigorous approach, would ensure the demographic similarity of the groups; be more conservative about what is considered a “significant” result; careful planning of the analyzes to be performed – this could increase our knowledge of the effects of PFAS. But as it stands, it tells us very little.
However, the authors released their study to the press along with a statement that governments should ban the use of PFAS in “everyday products”. Scientists are, of course, entitled to their opinions, but making policy recommendations based on such meager data seems overkill.
None of this means that PFAS are definitely not dangerous in any sense, or that proponents of the idea of ”PFAS are dangerous” are generally unduly concerned. You might think that banning these products is in line with the precautionary principle, even though we don’t have absolutely solid evidence of their effects. Also, the points above about fertility don’t say anything about fertility. another Advocate statements about the health effects of PFAS.
But the evidence linking PFAS and fertility problems is weak and surrounded by important unanswered questions. For now, if this is the quality of the evidence put forward, governments can be forgiven for not taking these proponents too seriously.
Source: I News
With a background in journalism and a passion for technology, I am an experienced writer and editor. As an author at 24 News Reporter, I specialize in writing about the latest news and developments within the tech industry. My work has been featured on various publications including Wired Magazine and Engadget.