Exposure to Endocrine-disrupting Chemicals Associated with Low Serum Testosterone

A new study showing significant negative correlation between phthalate absorption and testosterone levels adds considerably more weight and significant new details to a growing body of research.

Previous research has shown that phthalates such as di-2-ethylhexyl phthalate (DEHP) reduce testosterone in rats and are negatively associated with testosterone levels in humans, but most of the studies were small in size and narrowly focused on particular chemicals or populations.

The new study, on the other hand, used data from a National Health and Nutrition Examination Survey to investigate relationships between serum testosterone and 13 different phthalates in 2,208 men and women of all ages.

Researchers found significant negative correlations between exposure to many phthalates and overall testosterone levels, but correlation sizes varied widely among the different segments of the study population. In general, the associations proved stronger among adult women than adult men.

Exposure to several of the chemicals was associated with testosterone reductions of more than 15% for women aged 20-60. One compound, mono-benzyl phthalate, was associated with a 24% reduction in testosterone among women aged 40-60.

Among adult men, however, researchers found far fewer significant correlations. Only high concentrations of DEHP and dibutyl phthalate were associated with lower testosterone and only in men age 40-60. These findings contradict previous research, which has found significant negative correlations between phthalates, particularly DEHP, and testosterone levels in younger men.

The analysis uncovered far more cause for concern about the effect phthalates have on younger men. Indeed, among boys 6 to 12, DEHP exposure was associated with a 29% decrease in testosterone levels.

The study authors believe they are the first to undertake any significant work on the possible effects of many phthalates on women and children and that many of their findings are, therefore, entirely novel.

They also believe that the paper, which was just published in the Journal of Clinical Endocrinology & Metabolism, has significant implications for public health.

In a news release that accompanied publication of the study results, lead author, John D. Meeker, MS, ScD, of the University of Michigan School of Public Health in Ann Arbor, MI, said, “Low testosterone levels in young boys can negatively impact reproductive development, and in middle age can impair sexual function, libido, energy, cognitive function and bone health in men and women.”

“While the study’s cross-sectional design limit the conclusions we can draw, our results support the hypothesis that environmental exposure to endocrine-disrupting chemicals such as phthalates could be contributing to the trend of declining testosterone and related disorders,” Meeker said. “With mounting evidence for adverse health effects, individuals and policymakers alike may want to take steps to limit human exposure to the degree possible.”

Meeker suggested that something reasonably simple such as mandatory labeling might limit damage to people in those groups that appear most at risk.

The study authors did note several limitations to their work, beyond its retrospective nature and the cross-sectional design.

It does not, for example, provide any clues about how phthalates might work upon the body to reduce testosterone production or even if the different compounds, which are used to make flexible plastics and many beauty products, all work upon it in the same general way. It also provides no clue about whether some individuals are more susceptible than others.