"If this continues, by 2050, 41 percent of men will be infertile."
Harmful chemicals commonly found in the home could be to blame.
On average, sperm counts declined by a little more than one percent each year. At that rate, the share of men who are infertile would now be around 12 percent. And if that continues, by 2050, 41 percent of men will be infertile.
Only about 1.9 percent of all babies born in the US were conceived using artificial reproductive technology. By 2050, that will change, claims Dr Swan her new book. Dr Swan predicts that by then, a large proportion of people around the world will not be able to conceive without technological assistance.
That will be the result of declining sperm count among men around the world, she says. There are many drivers of infertility, but Dr Swan has homed in on a sneaky prime suspect: household chemicals called phthalates.
In 2017, Shanna Swan of the Mount Sinai School of Medicine in New York and Hagai Levine of Hadassah-Hebrew University in Jerusalem, along with six other researchers, estimated the average sperm count for 43,000 men in 55 countries across the world. The data, from 185 previously published studies, suggest that sperm counts fell by about 25% between 1973 and 2011 (see chart). But the academics performed a regression analysis that controlled for variation in the studies' sampling technique, their potential sample bias, the age of men and their level of abstinence before a sample was taken. They found that sperm counts had in fact fallen by about 50% in Western countries over the period. Although the data were less plentiful, similar trends were observed in developing countries, too.
Dr Swan's new book, “Count Down”, released earlier this year, investigates why this decline has occurred. The most likely culprit, she argues, is the proliferation of harmful chemicals such as bisphenol A (BPA)—which is most commonly found in household plastic goods. Humans’ endocrine systems, which produce hormones including testosterone and oestrogen, can be adversely affected by these chemicals. In some cases they reduce fertility among both men and women. One study, conducted in Boston, looked at nearly 500 young men who hoped to donate sperm. It found that the share of applicants who were sufficiently fertile to donate had fallen from 69% to 44% in the ten years to 2013.
BPA chemicals may not be solely to blame. Another study, published by Environmental Pollution in 2018, collected the semen samples of 5,000 men living in northern Italy between 2010 and 2016. By geocoding the men’s home addresses it found that sperm counts deteriorated most when air pollution was highest.
Even if BPA chemicals are not the sole cause of the decline in sperm counts, regulators have been slow to catch on to the proven harm they cause. In 2007 the European Union implemented REACH, a set of regulations on the import and production of hazardous chemicals. America and the EU have since banned the use of BPA in baby bottles but the chemical is still allowed in the linings of food cans. The decline in sperm counts, were it to deteriorate further, could have dire consequences. Alarmingly, if the rich-world trend observed by Dr Swan in her 2017 study continued until 2045, it might render half the men of Europe and North America infertile. That looks unlikely for two reasons. The effect of BPAs on sperm may diminish as their counts decline; and already fewer BPA chemicals are being used.