Sperm quality from healthy young men in the US has dramatically slumped over the past 16 years, as revealed by a new study. The culprit is not clear, but the researchers think it might be associated with the changes in lifestyle and perhaps environmental contaminants messing with their hormones. 

Scientists at the Reproductive Medicine Associates of New York analyzed more than 176,000 sperm samples collected from over 3,500 donors, healthy 19 to 38-year-olds, from nine different locations across the US between 2005 and 2021.

After controlling for their body mass index (BMI), the researchers noted a significant decline in the concentration of sperm in the semen, sperm motility, and the total motile sperm over the 16-year period. These changes were seen across all of the studied geographic regions.

The paper was presented at the annual meeting of the American Society for Reproductive Medicine

Declines in sperm quality in many parts of the world, especially developed countries, have been seen since the 1990s. Some experts have previously suggested the decline might have something to do with the development of more accurate means of recording sperm quality, not an actual decline in sperm quality. It’s also been pointed out by others that sperm counts have a very wide range of natural variability and the “optimal” sperm count is not clear. However, the relatively recent decline in sperm quality is a trend that appears time and time again. In 2017, a colossal meta-analysis found that the sperm count of “Western men” had declined by 50 to 60 percent between 1973 and 2011.

Clearly, this is a worrying pattern. Although the new study didn’t determine how this might impact fertility, it’s known that lower sperm quality can make it more difficult to conceive naturally.

The research did not look to explain why this trend is occurring. However, in their conclusion they suggest there could be a link to lifestyle changes, such as diet and stress, or even increased exposures to endocrine-disrupting chemicals.

Endocrine disruptors are chemicals that may interfere with the hormonal system of animals. Since certain hormones, namely testosterone and Follicle Stimulating Hormone (FSH), are necessary for healthy sperm production, disruption to hormones is thought to have some link to sperm quality.  

We can find endocrine-disrupting chemicals in everything, from the food we eat to everyday household products. They’re sometimes called “everywhere chemicals” because they’re so prolific in the developed modern world. One especially notorious group of chemicals defined as endocrine disrupters are phthalates, a prolific group of chemicals used to make plastics more durable that can be found in hundreds of everyday items, from kids’ toys and food packaging to hair sprays and paints.

Once again, the underlying cause of this trend, as well as its potential impact on fertility, is not still not known. Some have also suspected that the trend may be overstated and the fears are overblown. Nevertheless, it has led some scientists to fear that parts of the world may soon enter a significant collapse of fertility.

[H/T New Scientist]

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