© Dr Tony Brain/Science Photo LibraryHuman sperm. Coloured Scanning Electron Micrograph (SEM) of several mature human sperm (also called spermatozoa). Sperm are the motile male sex cells produced in the testis. Each sperm is about 65 micrometers long and broadly divided into head (red), neck and tail (blue) regions. A pear- shaped head contains the nucleus and genetic material of the male needed to fertilize the female egg (ovum). The head is joined to the tail by a short neck. The sperms tail enables it to swim by whiplash movements, an action that propels it to reach the ovum - Dr Tony Brain/Science Photo Library
Sperm counts are falling at a rate that threatens the long-term survival of the human race, a leading epidemiologist has warned.
In a new book, Shanna Swan, a leading environmental and reproductive epidemiologist at Icahn School of Medicine in New York, warns that there is a looming fertility crisis comparable in its impact to climate change.
She projects that if sperm counts continue to fall the current rates they will reach 'zero' by 2045.
To blame, she says, are lifestyle changes that alter hormone balances and exposure to "everywhere chemicals" that impair the endocrine system of chemical messaging in the body.
Additional factors, Prof Swan says, are smoking tobacco and cannabis and increased obesity.
In a research paper published in 2017 that she co-authored, Prof Swan found that total sperm count in the Western world had fallen 59 per cent between 1973 and 2011.
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If you look at the curve on sperm count and project it forward - which is always risky - it reaches zero in 2045," Prof Swan told Axios, a US news site.
Her new book, Count Down, expands on that research and argues that the fertility crisis is as serious as climate change.
"The climate crisis has been accepted - at least by most people - as a real threat. My hope is that the same will happen with the reproductive turmoil that's upon us", Prof Swan writes.
Fertility rates across the world have been falling for decades, with the average number of children born per woman falling from 5.06 in 1964 to 2.4 in 2018.
Much of that fall is associated with the positive results of economic development. Nevertheless, Prof Swan writes in the book that there is clear evidence of biological factors at play and not just socio-economic ones.
As well as falling sperm counts, Prof Swan identifies increased rates of miscarriages and impaired fecundity, a broad term for conception difficulties in couples, as evidence of a wider problem in the West.
She blames "everywhere chemicals" such as phthalates and bisphenol-A, which are found in cosmetics, pesticides and plastics, as well as lifestyle changes.
"Chemicals in our environment and unhealthy lifestyle practices in our modern world are disrupting our hormonal balance, causing various degrees of reproductive havoc," Prof Swan writes.
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