The Book in a Nutshell
In 2017, Shanna Swan and a team of fellow researchers published a study that shocked the world. The results suggested that in just forty years, the western world had experienced a drop in sperm count of more than 50 percent. In Count Down, Swan explores exactly how our reproductive health has changed and why, pointing to a range of lifestyle and environmental factors, notably including the role of endocrine-disrupting chemicals (EDCs) in our everyday lives.
Book Summary: The Key Ideas
#1: The Worrying Decline of Testosterone and Sperm Count. Research found that sperm counts have declined by more than 50% in the last 40 years. Studies also show that all-round reproductive health is in decline, with declines in testosterone, sperm quality, miscarriage rates and other fertility issues.
#2: The Reproductive Programming Window. The first trimester of pregnancy is one of the most important defining windows for the child’s future reproductive health. What a mother is exposed to or consumes during this window can influence sperm count, testosterone, and other fertility metrics.
#3: Lifestyle and Chemical Causes of the Reproductive Decline. Our lifestyle choices can contribute to dramatic declines in reproductive health (e.g. diet, smoking and alcohol). Swan’s particular area of interest, however, is endocrine-disrupting chemicals (EDCs), which are found in a wide range of everyday consumer products. Research suggests that exposure to certain EDCs can diminish sperm count and quality, as well as having a wide range of other impacts on reproductive health.
#4: The Physiological, Environmental and Demographic Consequences. The worrying decline in reproductive health raises risks of other physical health problems such as cancer. The demographic impacts pose important questions around economic policy. And our continued use of EDCs is having profound environmental impacts on other species that require urgent action.
Book Notes: The Key Ideas in Detail
The below are more detailed book notes on the key ideas from Count Down by Shanna Swan. These notes do not by any means cover the full breadth of the book and are instead intended as an introduction to the key themes, from which to decide whether to read the full book.
Key Idea #1: The Worrying Decline of Testosterone and Sperm Count
In a now famous 2017 study, Swan and team found that sperm counts have reduced by more than 50% across the western world in just the last 40 years. Researchers have also observed similar declines in testosterone levels across the world.
This worrying trend isn’t just a western phenomenon. Other studies have shown sperm count and testosterone declines across South America, Asia and Africa.
Importantly, it’s not just sperm count and testosterone that is diminishing; it’s sperm quality too.
Scientists evaluate sperm quality by looking at concentration (density of sperm in semen), vitality (% of sperm that are alive), motility (swimming ability) and morphology (size and shape). On all these measures, the world seems to be in decline on average.
Swan cites several studies, some showing a sharp decline in sperm quality in periods as short as 10 years during the 2000s.
The fertility crisis isn’t limited to men either. Fertility rates have plummeted across the western world, and this can’t solely be explained by social factors.
Girls also appear to be experiencing a rise in what’s known as “early puberty”, with menstrual cycles starting earlier than several decades ago. This brings with it psychological implications but also greater physical health risks, such as an elevated probability of earlier breast cancer.
Additionally, there is an increased prevalence of endometriosis and polycystic ovary syndrome cases among women.
Swan also explores the emergence of gender fluidity and identity issues. While many suggest that the rise of gender identity issues and gender fluidity reflects greater social permissions, Swan believes that our exposure to certain chemicals (EDCs) may have played a role too. For example, a rise in “intersex” babies has been noted. Swan points to research that suggests there is a link between prenatal exposure to EDCs and a higher risk of genital malformations in male newborns.
This link to EDCs also seems to extend to behaviour. In one study, monkeys exposed to bisphenol A (BPA) in the womb exhibited more female behaviour after birth. A similar link has been drawn to high exposure to phthalates.
Key Idea #2: The Reproductive Programming Window
“The most sensitive timeframe for reproductive tract development is the first trimester of pregnancy”.
This period, known as the “reproductive programming window”, is when the genitals and cells that will later produce sperm are formed.
As Swan notes, this window is crucial for sex differentiation in the developing fetus. In fact, the extent to which genitals develop depends on testosterone levels present at this time. Disruptions to the hormonal balance during this reproductive programming window can lead to a variety of problems, such as lower sperm counts, birth defects and shorter anogenital distance (AGD).
“One way or another, what happens in the womb doesn’t stay in the womb.”
AGD, in particular, is a very important measure of reproductive health. Swan and her research team have shown that shorter AGD is associated with smaller penis size and lower sperm count. Exposure to EDCs (see Key Idea #3) during the reproductive programming window, such as phthalates found in plastics, seems to be linked to shorter AGD.
In essence, then, our habits and consumption have a significant impact on the future reproductive health of our children, particularly in the first stage of development in the womb.
As Swan puts it:
“It’s not just about what you consume; it’s about when you consume it.”
Key Idea #3: Lifestyle and Chemical Causes of the Reproductive Decline
There are a large number of lifestyle factors that can also harm reproductive health. Swan gives particular attention to body weight, smoking, alcohol intake, diet, exercise, stress and some drugs.
The summary isn’t particularly surprising. An unhealthy weight, smoking, high alcohol intake, inadequate exercise and high exposure to stress are all correlated with lower levels of sperm quality and elevated risks of other fertility issues in both men and women.
The good news with these lifestyle factors is that much of the damage seems to be reversible – for men at least. Women unfortunately cannot replenish their eggs, and so damage is in some cases less reversible.
Swan’s main area of research interest is that of endocrine-disrupting chemicals (EDCs). EDCs can not only cause hormonal abnormalities and undermine our reproductive health, but they can also have a wide range of other adverse physical health impacts.
Swan highlights several important categories for these chemicals:
- Phthalates: This is a range of chemicals found in plastic and vinyl, medical tubing and devices, toys, some personal care products (e.g. perfumes and shampoos), and other household items such as floor coverings. The most worrying types of phthalates are those that decrease testosterone production. The worst type seems to be chemical called DEHP. Exposure during pregnancy has been linked to shorter AGD, lower sperm quality and lower testosterone. Exposure during adulthood also seems to have similar deleterious effects on the reproductive health of men and women.
- Bisphenol A (BPA): Ubiquitous in plastics for food and drink, BPA has what Swan calls “estrogenic properties”. Studies suggest that high exposure may decrease sperm quality and count, as well as having ripple effects from father to child. It is also linked to higher miscarriage risk in women.
- Flame retardants: Added to materials to slow or prevent fire growth, flame retardants have been linked to higher risks of miscarriage, altered timing of puberty and thyroid issues.
- Pesticides: High pesticide exposure in urine has been linked to lower sperm concentration and motility.
Key Idea #4: The Physiological, Environmental and Demographic Consequences
Swan separates some of the broader consequences of the decline in reproductive health into three categories: physiological, environment and demographic.
Physiological Consequences:
Adverse reproductive impacts can also lead to significant long-term health problems such as cancer and even premature mortality.
Importantly, evidence is increasingly showing that lifestyle and chemical-related causes of poor reproductive health can also be passed on in epigenetic code. Studies of EDCs suggest that impacts compound with the same exposure from generation to generation (using mice for the model).
Swan argues that the fact that male sensitivity to environmental hormones increases with successive generations may partly explain the drastic drop in sperm counts observed over the last 40 years.
Environmental Consequences:
The chemicals we have released into the environment also have far-reaching existential effects for other species. Swan points to the extent of ocean pollution with these chemicals in the form of our waste, the decline in insect and bird populations, and water contamination.
While some steps are progressing, we require urgent action both to clear-up contamination and stop further contamination (by regulating EDCs).
Demographic Consequences:
With fertility rates plummeting to record lows, the western world faces an impending demographic time bomb. At point will arrive whereby the labour force cannot support those in retirement age. Policymakers seem to be unprepared for this dramatic demographic shift.
The ratio of men to women born (the “secondary sex ratio”) is also changing. Studies suggest that exposure to certain environmental and personal stressors can lower the chances of males being born. This similarly creates a challenge in reversing the decline in fertility rates.
“Even if the will is there to reproduce and increase the birth rate, the machinery isn’t as functional as it used to be, for men or women.”
Swan points out that remarkably, human beings now meet 3 out of 5 of the endangered species criteria.
In the final section of the book, Swan sets out some personal actions we can take to change our lifestyle and reduce our EDC exposure (such as avoiding plastic use in the kitchen and avoiding certain bathroom products).
She then turns to the regulatory and testing landscape and suggests that the burden of proof needs to move from the public to manufacturers urgently:
“We are all essentially unwitting participants in a chemical game of reproductive Russian roulette because regulation of the chemical and manufacturing industries continues to operate on a “business as usual” basis, with chemicals considered safe until they’re proven guilty.”
You can buy the book here or you can find more of our book notes here. For further related reading, try Lifespan by David Sinclair and Hooked by Michael Moss.
