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April 22, 2022

Climate change and male fertility

According to the CDC, climate change influences human health in a myriad of ways — from increased respiratory and cardiovascular disease to decreased mental health. There’s also emerging evidence that climate change can negatively impact male fertility and sperm health. Let’s explore what the research says about how climate change may affect reproduction, other environmental effects on fertility, and steps you can take to stay healthy. 

Key takeaways

  • Animal studies show that increasing temperatures can hinder sperm production and that heat waves consistently impair male reproductive health.
  • Other environmental issues that may affect male fertility include poor air quality and endocrine disruptors found in common everyday items like plastics. 
  • Healthy lifestyle habits and sperm freezing can help protect fertility in the face of environmental threats.

What is climate change?

Climate change describes long-term shifts in temperatures and weather patterns in a particular region. These shifts may be caused naturally, through variations in the solar cycle, or they can be a result of human activities, namely the burning of fossil fuels like coal, oil, and gas. These fossil fuels produce greenhouse gas emissions that trap the sun’s heat and drive up temperatures. 

Since the 1880s, Earth’s average temperature has risen by at least 0.14°F every decade. And in fact, the rate of global warming over the past 40 years has been more than twice that: 0.32°F increase, per decade, since 1981. This increase has resulted in regional and seasonal temperature extremes, reduced snow cover and sea ice, intensified heavy rainfall, and an altered habitat for plants and animals. It also threatens our overall health.

What the research says about climate change and male fertility

One aspect of our health under threat is fertility, especially when it comes to sperm health. Several animal studies show that sperm are especially vulnerable to the effects of climate change, and experts say insects and other creatures “can be used as a proxy for people.” Here’s what the research says:

Animal studies show increasing temperatures may impact sperm production

Hollywood movies about human extinction often involve giant asteroids or extraterrestrial creatures. Researchers in a wide-ranging 2021 study show that climate change may be just as menacing, but in a more subtle way. While rising temperatures can and do contribute to disease, food scarcity, dangerous weather conditions and more, they may also impair sperm production, reducing the human and animal populations.

Some research has looked at the common fruit fly, comparing species in tropical and mid-latitude locations versus other widespread locations. Experts have found the tropical and mid-latitude species were more at risk for extinction because of the rising temperatures in these areas.

Why? While some experts originally believed the threat of extinction was related to the organism’s upper critical thermal limits (the maximum body temperature that can be tolerated before they stop moving and die) researchers in the 2021 study found that male fertility thermal limits were an even better indicator of their vulnerability.

Male fertility thermal limits tend to be far lower than critical thermal limits. In other words, while a fruit fly might fall into a heat coma and die at a particular temperature, its ability to reproduce is already impaired at a lower temperature — preventing future generations of fruit flies from being born and rendering the fruit fly species extinct through infertility.

The researchers also found little evidence of adaptive responses to warming in any fruit fly species. That means the common fruit fly, at least, doesn’t seem to be able to evolve as quickly as our planet is warming. This suggests a dire conclusion: that species are living closer to their upper male fertility thermal limits, and evolution isn’t able to keep up to rescue these populations from the possibility of extinction.

Another study looked at the red flour beetle. This research also found that rising temperatures negatively affected sperm function and reproductive success, with male sperm production declining by 75%. The sperm that was produced often struggled to migrate into the female tract, and were more likely to die before successful fertilization.

This study concluded that heat waves consistently halved male reproductive fitness in the red flour beetles — and the problems didn’t stop when the temperature returned to normal. Researchers also discovered that offspring produced by males who had lived through heat waves had shorter life spans and also had impaired reproductive capabilities.

What about human research into climate and male fertility?

In general, we have some good evidence to suggest that warmer temperatures are related to lower sperm production. For one, UCLA environmental economist Alan Barreca has noted that more births occur in August and September in the US, nine months after the coldest part of the year. In his study published in the journal Demography, he reported that days with a mean temperature above 80°F were correlated with a large decline in birth rates 8–10 months later. This is likely not because people have less sex in hot weather — they actually have more sex — but because of the weather’s effect on sperm production.

Comparison of semen analyses collected in the summer and winter have found similar results. A 1988 study of men in New Orleans found that semen specimens collected during the summer had “significantly lower sperm concentration, total sperm per ejaculate, percent motile sperm, and motile sperm concentration than samples provided at other times of year,” especially for men whose jobs were not air-conditioned.

The same research team followed up with a small study of men in San Antonio in 1990. Again, they found that summer spelled “significant reductions” in sperm concentration (32%), total sperm count (24%), and sperm motility (28%). They also found that the impact of heat was most detrimental on men who already had lower semen parameters.

While none of this exactly looks at how rising global temps could impact male fertility — and there’s not a direct line from warmer climates to infertility — it’s clear that warmer weather and heat waves have a significant, negative effect on sperm health for humans as well as animals.

Other environmental effects on fertility

Climate change isn’t the only environmental threat to fertility. Researchers have noted a connection between air quality and male fertility, and discovered that endocrine disruptors (chemicals found in plastics and pesticides, among other sources) can also interfere with the hormonal and reproductive systems of both sexes. Here’s what the research says:

Air quality

Researchers have long suspected that environmental factors contribute to infertility. A 2000 study from the Czech Republic found that elevated air pollution resulted in both a decrease in sperm motility and a degradation of sperm morphology. A more recent 2020 study that looked at the effects of air quality on female fertility found that with every small increase in pollution exposure, there was a 7% decrease in markers of ovarian reserve.

A study of over 10,000 couples in China found that air quality was strongly tied to fertility. Couples in the upper quartile of pollution exposure had nearly twice the risk of experiencing infertility, compared to couples in the lowest quartile. There is also evidence that exposure to air pollutants may contribute to a higher chance of premature birth, low birth weight, and miscarriage.

Endocrine disruptors

Endocrine disruptors are chemicals that interfere with the function of hormones in the endocrine system. Endocrine-disrupting chemicals (EDCs) can be found in everyday products like canned food, water bottles and other plastic food containers, fertilizers, pesticides, cosmetics, and toys.

Research shows that persistent and long-term exposure to these chemicals may have negative effects on human reproductive health by interfering with the production and action of the sex hormones. Animal studies have shown that endocrine disruptors are related to reduced testosterone production, a decrease in sperm motility, an increased risk of azoospermia, and abnormal sperm morphology. There is also evidence that exposure to these chemicals may increase prostate cancer progression.

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What you can do to safeguard your fertility 

Even if you recycle, drive an electric car, or take other actions to minimize your carbon footprint, you cannot solve the climate crisis alone. However, there are steps you can take to safeguard your fertility no matter what. Here are some ideas:

  • Support legislation that addresses climate change. The increasing temperature of our planet has real, detrimental effects on our health.
  • Stay cool. Do everything you can to reduce the impact of warmer temperatures on your sperm. Wear loose-fitting underwear, avoid sedentary positions, minimize hot tub or bath use, and keep laptops and cell phones away from the scrotum, which can add heat and radiation to the area.
  • Use products free from BPA and DEHP, two common endocrine disruptors that can negatively impact fertility.
  • Refrain from smoking, which can worsen your air quality and take a toll on the reproductive system.
  • Check your sperm with an at-home semen analysis kit to find out how healthy your sperm is right now.
  • Consider freezing your sperm to preserve your fertility for years to come.

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