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This story in the Guardian quotes Shanna Swan, professor of environmental medicine and public health at Mount Sinai school of medicine in New York City. She makes a number of claims about the impact of chemicals used to modify the properties of plastics. Some of these chemicals mimic testosterone and oestrogen, and Professor Swan believes that these are causing a reduction in fertility in both men and women, to the point where, if the trend continues, by 2045 most couples will need assisted reproduction to have a baby.

My question is: how much of this is true? Is there a consensus view among the relevant scientists that chemicals absorbed from plastics are a significant cause of reduced fertility in the general population?

Some specific claims quoted from the article:

  1. I am not saying other factors aren’t involved [in sub-fertility or reproductive problems]. But I am saying chemicals play a major causal role. (My square bracket)

  2. When a colleague and I looked at the change in impaired fecundity [the ability to have children] we were surprised to see younger women had experienced a bigger increase than older age groups. (That square bracket was in the original article)

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  • There is a related question about the data underlying the claim, sperm counts. That raw data is not as unambiguous as most commentators seem to assume and it is certainly not good enough to justify a claim about a specific cause: skeptics.stackexchange.com/q/7160/3943 – matt_black Mar 29 at 14:27
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    This seems to be two separate questions: 1) Do these chemicals actually cause declines in fertility? and 2) If such a decline exists, is it a "crisis", or (given the current unsustainable population levels) a blessing? – jamesqf Mar 29 at 17:48
  • I've seen discussion in the literature linking a discernable reduction in the age of puberty to plastics that mimic estrogen, testosterone and other sex-related hormones, things like scientificamerican.com/article/… and chej.org/2012/04/02/…. I've never seen anything definitive though. – Flydog57 Mar 30 at 1:48
  • @jamesqf I avoided the word "crisis" in the text, but I didn't think to remove it from the title. I have now done so. "Crisis" is unnecessarily emotive and beside the point of the question, which is about the basic claim. Whether it is a "crisis" is a question for Politics.SE. – Paul Johnson Mar 30 at 6:04
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    i hope so; there was way too much traffic on the way to work this morning. – Jason C Mar 30 at 19:54
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Western world

Indeed, according to the Independent there is a crisis regarding fertility rates. But rather interestingly the same trend has not been observed in other parts of the world such as South America, Africa, Asia, though admittedly fewer studies have been carried out in those areas.

Also, it is indeed true that one of the suspected factors, along with pesticides, stress, smoking, obesity, is chemicals in the environment. But most important to note is the fact that further research is still required before anything conclusive can be ascertained.

Independent

Sperm counts have plunged by nearly 60 per cent in just 40 years among men living in the West, according to a major review of scientific studies that suggests the modern world is causing serious damage to men’s health.

Pesticides, hormone-disrupting chemicals, diet, stress, smoking and obesity have all been suggested as possible reasons behind the dramatic declines but experts say more research is urgently needed

The same trend was not seen in other parts of the world such as South America, Africa and Asia, although the scientists said fewer studies had been carried out there.

Diet

However, given that one of the biggest factors that separate different cultures is diet, it may come as no surprise that one of the main theories for the cause of lowering fertility rates is dietary, according to a recent study of 2,935 men, reported by NCBI.

NCBI

In a cross-sectional study of 2935 young Danish men unaware of their fertility status, higher adherence to the Western diet pattern was associated with lower sperm quality than that of men with the lowest adherence. Conversely, higher adherence to the prudent diet pattern was associated with higher sperm quality.

These findings suggest that adherence to healthy diet patterns, a potentially modifiable lifestyle factor, is associated with better semen quality and potentially more favorable fertility potential among young men.

Are chemicals in plastic causing a fertility crisis?

Nothing conclusive can be ascertained until further research is carried out. But certainly chemicals are believed to be one of the many hazards, with diet perhaps currently being taken very seriously.

Currently there is no reason to believe that chemicals in plastic are the only factor, nor even necessarily the main factor.

Like Prof. Allan Pacey, Professor of Andrology, University of Sheffield, said to the Science Media Centre, it is too premature to conclude that this is due to man-made chemicals. (Not a direct quote - words to that effect)

SMC

“Interestingly, the paper concludes that the sperm counts may have seen the greatest decline in the post industrial countries of North America, Europe and Oceania compared to others in Asia, South America and Africa. However, while it would be easy to conclude that this represents a real global difference, perhaps driven by greater exposure of pregnant women or adult men to more man-made chemicals, I think it is too premature to make this conclusion.

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    Prof Swan (from the original post) is one of the group being quoted, so while this adds weight to the Guardian article it is not independent confirmation. – Paul Johnson Mar 28 at 17:02
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    @Paul Johnson Apologies, I maybe gave the wrongful impression that I was looking to prove that it "is" about man-made chemicals. I have edited the post to include Alan Pacey's words. Thus I do not need to verify Prof Swan, as I am not saying he is correct. I am merely agreeing that it is believed to be the case in certain circles, but that there is no conclusion to date. – John Strachan Mar 28 at 17:50
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    No need to apologise: its a really good answer as far as it goes. +1. – Paul Johnson Mar 28 at 21:28
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    Is this actually proof for a crisis? A reduction in sperm count is not necessarily a crisis. Even if that brings down the population growth/change, which might not be the case due to higher child survival rate, whether a slight reduction in population would be a crisis would be a question of interpretation. Is it assessed as a crisis by a reputable source (other than a tabloid newspaper that finds a crisis every week)? Is there a direct line of thought backed by data that makes it a crisis? And if population growth reduction is likely and considered a crisis, is it the main factor? – Frank Hopkins Mar 28 at 23:36
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    Have the studies of diets controlled for obesity? Something like 50% of Americans are obese, and it has a lot of negative health impacts. – nick012000 Mar 29 at 3:28
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Are chemicals in plastic causing a fertility crisis?

I will be more assertive: SOME chemicals in plastics, or plastic coating, have proven effects on hormones and fertility.

For example bisphenol A, (that you could find a few years ago on baby bottles, and metal cans) : https://en.wikipedia.org/wiki/Bisphenol_A#Health_effects

However, draw a solid, scientific conclusion, (with good statistic analysis, and no bias), of PLASTIC chemicals being the cause of FERTILITY crisis, is something that would require the results of a specific scientific study over years.

Otherwise, professors will tell you that "it is too premature to conclude", of that "no conclusion could be made". It doesn't mean this is true, nor that it is false either.

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There are two quite typical problems with the claim:

  • It's impossible to strictly prove a negative (as in "X has no impact on health"). It's only ever possible to evaluate a specific chemical compound, not "plastic" in general, and only in specific conditions.

  • Correlation does not prove causation in simple statistical studies (you need a randomized double blind study like in drug testing to determine if the health impact really comes from X, and not from other factors which come together with X)

For example, here's a study which is focused on health effects of BPA which is theorized to have an impact on reproductive health because it is structurally similar to estrogen. The conclusion is that normal exposure (through plastic used in food packaging) has no significant impact:

TOTBPA was observable only in individuals with exposures 1.3–3.9 times higher than the 95th percentile of aggregate U.S. exposure. [...] During these high dietary exposures, TOTBPA concentrations in serum were undetectable in 83% of the 320 samples collected and BPA concentrations were determined to be less than or equal to LOD in all samples.

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