• Industrialized regions have low birth rates that will result in decreasing populations over time
• Declines in birth rates appear to be due to a mix of socioeconomic and cultural factors, and also human infertility
• Researchers should focus future studies about low birth rates on distinguishing biological from socioeconomic and behavioral factors
  

Fossil fuels refer to any fuel that’s found naturally in the earth. Examples include coal or gas that was formed from the remains of living organisms. Even though the sources of these fuels are ancient, the way that we use them for most of our energy needs is very modern. Fossil fuels only began to be the primary source of energy during the Industrial Revolution, which began in the mid-18th century.

Industrialization marked the transition from an agrarian society - an economy based on producing and maintaining crops and farmland, to an industrial society - an economy driven by the use of technology and machinery to enable mass production.

Industrialization really picked up steam (pun intended) in the mid-19th century with the proliferation of the steam engine, the invention of the internal combustion engine and the widespread utilization of electricity. This age of machines and technology continues to evolve to this very day.

Over the last 200 or so years, humans have unintentionally been conducting an experiment to find out what burning huge amounts of fossil fuels does to our earth, our air, our bodies, and our ultimately human health. Although chemicals from fossil fuels affect all of our organs and body systems, for the sake of this article, we’re going to stick with the effects of fossil fuels on our sperm health and semen quality - two huge factors in male fertility. 

Spoiler alert: it’s not good.

Over the last 50 years, the global fertility rate has fallen by half (2). Women use to have between 4.5 and 7 children during their lifetime. That number is now below 2.5 children. 

Much of that can be attributed to women entering the workplace, improved methods of birth control, evolution of gender roles and societal norms, and the cost of raising children. However, many couples who want to have children these days are struggling with infertility and must resort to costly and stressful fertility interventions due to a decrease in sperm health.

So how do we know that this really has to do with fossil fuels and not the other environmental and behavioral factors that we mentioned earlier? 

The Denmark study looked to see if the rise in poor semen quality, testicular cancers, and decreasing birth rates were linked to the ever increasing exposures that humans have to the toxic chemicals that directly or indirectly come from burning fossil fuels.

According to the study’s authors, fossil fuels serve as the raw material for more than 100,000 synthetic chemicals that are now ubiquitous in our modern lifestyles. These chemicals can be found in virtually every living creature. What the study found is that as our dependence on fossil fuels increased and the prevalence of these toxic chemical byproducts increased, our fertility and birth rates decreased.

Harmful chemicals from fossil fuels are found in all parts of our bodies, including our reproductive systems. The rise of these pollutants not only mirrors a decline in fertility in general, but it also mirrors the decline in sperm counts specifically.

Several studies have shown the sperm count has decreased over time:

• A 1992 study found a 50% decrease in sperm counts has occurred in men globally over the last 60 years (3). 
• A 2017 study found that the average sperm count of a man in 1973 was 337.5 million. In 2011, it had fallen to 137.5 million (4).

As you might expect, studies in animals have shown that when exposed to chemicals that disrupt the endocrine system, rats and mice suffer changes to their DNA that affect their reproduction. 

Niels Erik Skakkebæk, the lead author of the Denmark study, put it this way, “We know from numerous experimental animal studies that plastics, chemicals, and so forth can cause problems in animal reproduction. We cannot do such exposure studies in humans, that would not be ethical, but we know enough from animal studies to be concerned.” 

• Don't smoke. Seriously - smoking is bad for sperm and fertility.
• Maintain a healthy weight. Research suggests that high body mass index (BMI) is linked with lower sperm count and sperm movement.
• Eat healthy. Your mother was right - fruits and vegetables are great for you. Most importantly, they're full of antioxidants which can help improve sperm health.
• Manage stress. Stress can decrease sexual function and interfere with the hormones needed to produce sperm. Certain supplements have been shown to reduce the biological markers of stress and anxiety. 
  
• Exercise. Physical activity can increase antioxidant enzymes, testosterone levels, and other factors that lead to healthy sperm.
• Consume enough essential vitamins and minerals. Certain vitamin deficiencies can reduce fertility, such as copper and zinc. A daily multivitamin can help cover your bases.

1. Environmental factors in declining human fertility. doi: 10.1038/s41574-021-00598-8

2. Fossil fuels may be linked to fall in sperm counts, fertility. The Hill, December, 2021

3. Trends of male factor infertility, an important cause of infertility: A review of literature. doi: 10.4103/0974-1208.170370

4. Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update, November, 2017