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Phthalates from plastics, personal care products influence testosterone levels among men
Urinary biomarkers that detect the presence of phthalates were associated with testosterone concentrations among a representative sample of U.S. men, according to findings published in The Journal of Clinical Endocrinology & Metabolism.
“Interestingly, we found that the direction of these associations differed by the age of the men,” Melanie Jacobson, PhD, MPH, a research scientist in the division of environmental pediatrics at NYU Langone Medicine Center, told Healio. “For example, high-molecular phthalates, often used in plastic or polyvinyl products, were associated with lower testosterone concentrations among older men aged 60 years and older. However, low-molecular-weight phthalates, found in personal care products, were associated with lower testosterone concentrations among younger men aged 20 to 39 years.”
In a cross-sectional analysis, Jacobson and colleagues analyzed data from 1,420 men not taking sex hormone medications who participated in the 2013-2014 and 2015-2016 cycles of the National Health and Nutrition Examination Survey (65.29% white; median BMI, 28.4 kg/m²; 38% with obesity). Researchers stratified men by three age group: aged 20 to 39 years (n = 488), aged 40 to 59 years (n = 459) and aged at least 60 years (n = 482). Researchers investigated the association between urinary phthalate metabolites and total testosterone, estradiol and sex hormone-binding globulin, as well as free testosterone, bioavailable testosterone and free androgen index (FAI), examined as log-transformed continuous variables.
The researchers found that phthalate metabolites were not associated with sex hormone concentrations among all men; however, associations varied by age. Among men aged 20 to 39 years, low-molecular-weight phthalates were associated with a median 4.76% lower free testosterone (95% CI, –8.62 to –0.75) and a median 4.6% lower bioavailable testosterone (95% CI, –8.55 to –0.47). However, among men aged 40 to 59 years, low-molecular-weight phthalates were associated with higher free and bioavailable testosterone, and there was no association between low-molecular-weight phthalates and testosterone among men aged at least 60 years.
In contrast, high-molecular-weight phthalates were associated with lower total testosterone, free testosterone, bioavailable testosterone, estradiol and FAI levels among men aged at least 60 years.
“For example, for a doubling in high-molecular-weight phthalates, we estimated 4.92% lower testosterone (95% CI, –9.79 to 0.21), 4.68% lower free testosterone (95% CI, –8.4 to –0.81), 5.02% lower bioavailable testosterone (95% CI, –8.57 to –1.32), 3.74% lower estradiol (95% CI, –7.65 to 0.34) and 4.08% lower FAI (95% CI, –7.68 to –0.33%),” the researchers wrote.
There were no associations between high-molecular-weight phthalates and hormone concentrations observed for men younger than 60 years,
High-molecular-weight phthalates were associated with lower total, free and bioavailable testosterone among men aged at least 60 years.
“Our study was cross-sectional, which means that the exposures and outcomes were measured at the same time,” Jacobson said. “This makes it difficult to find out if the exposure caused the outcome. Studies focusing on times of hormonal flux, such as puberty, are important, as these may represent windows of increased vulnerability to environmental exposures such as phthalates.” – by Regina Schaffer
For more information:
Melanie Jacobson, PhD, MPH, can be reached at NYU School of Medicine, Division of Environmental Pediatrics, 403 E. 34th St., New York, NY 10016; email: melanie.jacobson2@nyulangone.org.
Disclosures: The authors report no relevant financial disclosures.
Perspective
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Phthalates are a very large family of chemicals used in a wide variety of products, from PVC pipes to food packaging to personal care products. We have known for a long time that certain phthalates can lower blood levels of testosterone in male rats and mice. Now, Woodward and colleagues report on their analysis of data collected by the CDC linking phthalate exposure to blood levels of testosterone in almost 15,000 men nationwide. It turns out that some phthalates were linked to low testosterone in men aged younger than 40 years, but that others were linked to low testosterone in men aged at least 60 years.
This has several important implications. First, it means that some of these chemicals may contribute to trends of lower testosterone and sperm counts in U.S. men. In addition, nearly 60% of men aged at least 60 years have testosterone levels below the normal range. Thus, phthalates may also be contributing to this trend as well.
What is interesting is that the kind of phthalates linked to lower testosterone levels in older men are those used primarily in plastics and polyvinyl production. In contrast, the phthalates linked to lower testosterone levels in younger men are those often used in personal care products. This information should help inform consumers about chemicals in everyday products and where they are found so that individuals can play a role in reducing their exposure.
It also must be recognized that these kinds of studies could fall prey to poor design. For example, it is mathematically true that the average American has one testicle. Of course, we know that if we stratify the population by sex, the value will be different. Thus, the work of Woodward and colleagues should gain credibility because of the intelligent way they stratified the population of men by age and the population of phthalates by, in this case, molecular weight.
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