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"Substantial declines in testosterone levels and
sperm quality have been observed in the United States and other
countries over the last several decades which and it urgently requires
explanation," Stahlhut said. "While we can’t say yet that phthalates
are a definite cause, I am certain they are on the list of chemicals
that demands careful study."
Phthalates have been widely used for more than 50
years, but only recently implicated as a possible health risk in
people. Animal studies have shown consistently that phthalates depress
testosterone levels. Recent human studies have found that phthalates
are associated with poor semen quality in men and subtle changes in
the reproductive organs in boy babies. This connection between
phthalates and testosterone helped to establish a basis for the study,
Stahlhut said.
Stahlhut’s group hypothesized that phthalates might
have a direct link to obesity, since low testosterone appears to cause
increased belly fat and pre-diabetes in men. They analyzed urine,
blood samples and other data from the National Health and Nutrition
Examination Survey. The NHANES is a large, multi-ethnic, cross-section
sampling of the U.S. population acquired routinely by the Centers for
Disease Control and Prevention. Researchers reviewed data from 1999 to
2002, the most recent years that phthalates levels were available. Of
the adult men available in NHANES, 1,451 had data on phthalate
exposures, obesity and waist circumference. Of these men, 651 also had
fasting glucose and insulin levels required to calculate insulin
resistance.
The analysis found that, as expected, several
phthalate metabolites showed a positive correlation with abdominal
obesity. Indeed, men with the highest levels of phthalates in their
urine had more belly fat and insulin resistance. Researchers adjusted
for other factors that could influence the results, such as the mens’
age, race, food intake, physical activity levels and smoking.
The phthalate family of chemicals is used in a
variety of products from cosmetics, shampoos, soaps, lotions,
lubricants, paint, pesticides, and plastics. Phthalates soften plastic
tubing, PVC, and are also used in the coating of some timed-release
medicines.
More than 75 percent of the United States
population has measurable levels of several phthalates in their urine,
according to the study.
"Unfortunately, there’s still a lot to learn about
phthalates," Stahlhut said. "The more difficult issue is what
combinations of common low-dose chemical exposures might be
contributing to these problems." |
