Sperm levels among men in Western countries has more than halved during the past 40 years - and, according to one study, could deplete to zero by 2045.

It’s unsurprising that the results of this research raised alarm bells around the world.

The film Children of Men is set in England in 2027, when an unknown catastrophe has rendered humanity infertile.

The world's youngest person has just died at the age of 18, and the movie follows the desperate journey of a young, black pregnant woman and attempts to reach the Human Project, and restore the future of the human race. 

Could this dystopian film become a stark reality in the not so distant future? There is a very heated debate.


Three years ago, leading environmental and reproductive epidemiologist Shanna Swan and her team of researchers completed a major study.

They found that during the past 40 years, sperm levels among men in Western countries had more than halved, and could deplete to zero by 2045. That would mean no babies. No more humans. 

Swan’s study found the major culprit of this fall in sperm count to be a class of chemicals called endocrine disruptors, which mimic the body’s hormones.

The chemicals include phthalates and bisphenol-A, which are everywhere, from plastics to pesticides in our food, from cosmetics to receipts, from waterproof clothes to electronics, from cleaning products to carpets. 

Phthalates get into our bodies by either passing from plastic packaging and pesticides into our food and drink, or from cosmetics absorbed into our skin.


Swan’s study also found that phthalate exposure was “widespread” in infants, and that the chemicals were found in the urine of babies who came into contact with baby shampoos, lotions and powders.

These chemicals are problematic as they interfere with hormone signalling, and development and function of male reproductive organs.

The study claimed that these phthalates were proven to lower testosterone levels and decrease certain measurements in babies such as anogenital distance - the distance from anus to genitals - which correlates to a lower sperm count. 

It’s unsurprising that the results of this research raised alarm bells around the world. However, a new study from Harvard has found flaws in Swan’s study, with problematic assumptions from the data around sperm count. 

The research from Harvard found that the earlier research had claimed there was a causal link between declining sperm counts and declining fertility - as well as between exposures to certain environmental chemicals and lower sperm counts.


Just because there is a correlation between two events, does not mean that one has caused the other. The correlation between sperm count and fertility could be a coincidence, or it could be caused by a completely different factor, such as nutrition, exercise, migration patterns, geographical environment and women’s fertility.

Women’s fertility is a key factor to include as focusing only on the male metric leaves out key interactions between sperm and egg. Sperm count varies within a wide range, and more of it is not necessarily an indicator of better health or increased fertility. 

Whilst the Harvard researchers praise Swan’s research at length for methodology and impact, they question what is meant by a "decline" in sperm count, as to date there is no definition for optimal sperm count due to lack of global statistics for sperm count 50 years ago, 10 years ago and today. 

There is no doubt that today there are couples needing infertility treatment – around one in six couples now today have trouble conceiving. Therefore research into fertility of both men and women is needed.

However, instead of using sperm count to study male fertility, researchers propose that we should be looking at bioavailability of sperm - the proportion of sperm which enters the body to have an active effect during intercourse - rather than count. 

This Author

Sophie Johnson is a zoology graduate and passionate conservation blogger from the UK.

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