Global sperm counts are falling. This scientist believes she knows why

This FT long read tees up its star protagonist, Shanna Swan, and her life’s research in the following manner: “The mystery is this. Since the late 1930s, sperm counts around the world appear to have dropped significantly. While the decline was initially observed in western countries, there is evidence of the same phenomenon in the developing world, and it seems to be accelerating. Swan, a Berkeley-trained statistician-turned-epidemiologist, believes she knows why.

For more than two decades she has devoted her life to studying the effects of “endocrine disrupting” chemicals (EDCs), which can interfere with the body’s natural hormones. These include pesticides, bisphenols, which harden plastic so it can be used in food storage containers and baby bottles, and phthalates, which soften plastic for use in packaging and products such as garden hoses. In recent years, traces of EDCs have been found in breast milk, placental tissue, urine, blood and seminal fluid.”

And here is Dr Swan’s disturbing conclusion: “…the innocuous products in your kitchen cupboard, bathroom cabinet or garden shed may be lowering sperm counts. They could also affect the reproductive systems of your unborn children. The implications of EDCs for human health don’t stop there: they can disrupt thyroid function, trigger cancer and obesity….

she described one of her pivotal discoveries: that AGD (Ano-Genital distance i.e. the span from the anus to the base of the penis) can act as a predictor of a man’s ability, years later, to conceive a child. It has provided evidence for her thesis that inadvertent exposure to EDCs in utero can inflict harm on a developing foetus….

…what has driven her into the public arena is a conviction that the world might be sleepwalking into a fertility crisis. If her hypothesis is correct, we need to overhaul how we cook, eat, produce and package consumer goods, and rethink industrial processes.”

The FT article provides more details on the chain of research exercises that lead Dr Swan to the conclusion that because of the exposure that pregnant women have to plastics, their foetuses are exposed to EDCs and this in turn reduces the AGD which in turn impacts male fertility.

Leaving aside her research, Dr Swan cites other research which validates here concerns about falling fertility levels, namely, a dramatic rise in assisted reproduction and surrogacies.

So how rapid is the drop in sperm count that Dr Swan has detected in her research on this subject (which itself has been continuing for nearly 30 years now)? “What she knew was that there was a trend, and it was rapid — a 50 per cent drop in mean sperm counts in 50 years. “That’s not evolution. That’s too fast,” she thought…A total of 185 studies were examined in detail, using meta-analysis methods not available to the Danish academics 30 years before. The conclusion was deeply unsettling. Sperm count appeared to have declined 52 per cent in 38 years, or something over 1 per cent a year….

…she accepts that a lower-than-average sperm count does not necessarily doom a man to childlessness, there is a consensus that once sperm counts hit a particular level — below about 40 million sperm cells per millilitre of semen — fertility can be impaired.”

Counterintuitively, Dr Swan’s work shows that this problem is worse in rural areas than in urban areas. Why might this be? “Hypothesising that some aspect of modern agriculture, particularly pesticides, might be affecting semen quality, Swan launched a pilot study, sending the Missouri men’s urine samples to the Centers for Disease Control and Prevention (CDC). The participants with poor semen quality were found to have significantly higher levels of eight pesticides compared to their counterparts in urban Minneapolis, whose semen quality was above average.

The findings added to a growing consensus that certain pesticides were harmful.”.

So what can be done given the massive scale of the plastic & pesticides problem? “Ironically, humans have ended up ingesting plastic, as particles and vapour. Chemicals from plastics leach out of containers into food, particularly when heated. Bottle-fed babies are swallowing millions of microplastic particles a day, a 2020 study showed, the health impacts unknown. An ingredient that was used in Teflon, PFOA, has been linked to cancer, ulcerative colitis and birth deformities. (DuPont, Teflon’s manufacturer, was found to have known about the health risks for decades, but only ceased production of PFOA in 2013.)…In 2008, for example, children’s toys and childcare items containing more than 0.1 per cent of three types of phthalates were permanently banned in the US. This year, the European Food Safety Authority recommended lowering the “tolerable daily intake” for BPA by a factor of about 20,000. (The European Medicines Agency is opposing the change.)

In April, G7 climate, energy and environment ministers issued a communiqué committing to “actively preventing chemical pollution, or . . . minimising its associated risks, including when caused by releases of endocrine disrupting chemicals””

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