Exposure to a group of chemicals called phthalates could be linked to poor sperm quality in men, according to a new study from researchers at Lund University in Sweden.
Nearly everyone has been exposed to phthalates, which give plastic its flexible quality. In one population-level survey, the Centers for Disease Control and Prevention found phthalate metabolites -- evidence that our bodies have absorbed and metabolized the compound -- in the general population.
While low levels of these chemicals haven’t been shown to be definitively harmful to our health, emerging research suggests that phthalates may be endocrine disrupters, which means that they could interfere with our hormones and affect things like the onset of puberty and cancer risk.
In this case, researchers found a relationship between phthalate exposure and lower sperm motility, meaning study participants' sperm struggled to effectively move in a straight line, the way it would successfully move through the female reproductive tract.
Lund University researcher Jonatan Axelsson analyzed the urine and sperm of 300 men between the ages of 18 and 20, theoretically the age a man would have the healthiest sperm. Axelsson found that if men had higher levels of the phthalate known as DEHP, or diethylhexyl phthalate, the lower their levels of sperm motility.
Motility is measured by sperms’ ability to simply move forward in a straight line; the slower they go, or the more deviations they take, the lower their motility grade. Axlesson found that the 25 percent of men with the lowest levels of DEHP metabolites in their bodies also had more sperm that moved well — 57 percent of them moved forward. Meanwhile, for the 25 percent of men in the study with the highest levels of DEHP metabolites in their urine, only 46 percent of sperm were moving forward. Axelsson controlled in his experiment for things like urine concentration, as well as the last time the participants had ejaculated.
But before you go toss every plastic bottle, remember that this study simply shows a correlation, and doesn’t establish whether phthalates caused lower sperm motility. Axelsson contextualizes his findings in a statement about the research, saying that there are studies that show two things: either phthalates levels are linked to lower sperm motility, or there’s no relationship at all between the chemical levels and sperm movement. The important thing to take away, he said, is that our body flushes phthalate metabolites out in a few days.
"The substances break down in the body within a few days, so there is no cause for immediate concern," said Axelsson. "However, we should be aware that there may be a problem and that it can be an important issue for further research."
It’s also important to remember that even the lowest motility range Axelsson observed is much higher than the lowest limits needed to conceive a child through intercourse. A 2010 World Health Organization survey of semen samples from over 4,500 men across 14 countries found that in men whose partners had conceived within 12 months (the threshold for normal conception), their progressive motility rate was 32 percent.
In other words, it’s an eyebrow raising result, but a lot more work needs to be done to before a causal link between phthalates and sperm quality is established.
Axelsson's research was published in the journal Environment International.
CORRECTION: A previous version of this story incorrectly stated that phthalates harden plastic. They help make it flexible.
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