Plasticizer related to lower hormone levels in men.

Jan 27, 2009

Meeker JD, AM Calafat and R Hauser. 2008. Urinary metabolites of di(2-ethylhexyl) phthalate are associated with decreased steroid hormone levels in adult men. Journal of Andrology doi:10.2164/jandrol.108.006403.

Synopsis by Jennifer Adibi

Adult men with average amounts of phthalates in their urine had lower levels of two important hormones -- testosterone and estrogen -- in their blood.

The hormones are necessary for normal sperm production and function.

This is the first study to show a relationship between phthalate levels and hormone levels in adult men. The phthalate levels "are representative of those found among the general US population," yet more research is needed to determine impacts on the men's health and fertility, say the authors.

The results, though, mirror how their rodent counterparts respond to similar phthalate exposures. In the rodent studies, di(2-ethylhexyl) phthalate, or DEHP for short, suppresses testosterone levels, which essentially demasculanizes the males by altering reproductive development and function.

Pthalates are used to make vinyl plastics flexible. The chemicals extend the life of perfumes in household and personal care products. People are exposed through food, water and air; at home, at work and outside. One well known source of exposure -- especially concerning for infants and children -- is plastic tubing and bags used in medical devices. Almost everyone living in the US carries pthalates in their bodies.

In this study, researchers measured breakdown products of DEHP and other phthalates in urine and compared those levels to hormone concentrations measured in the blood of the men. Metabolites indicate exposure to the "parent" chemical. The large sample consisted of 425 men who were seeking treatment for infertility.

The DEHP metabolites measured in the men's urine had the strongest association with the estrogen hormone estradiol. The more metabolites they measured in the men, the lower the levels of estrogen they found.

Animal studies find a similar trend in females. In those studies, the main metabolite of DEHP (called MEHP) blocks the synthesis of a key enzyme called aromatase. Aromatase converts testosterone into estradiol. As it turns out, the metabolite may block the enzyme in both males and females -- as the results of this study suggest.

The DEHP metabolites were also associated with less testosterone binding to a special protein in the blood -- the sex hormone binding globulin (SHBG). The protein carries the hormone to where it is needed in the body.  Less testosterone traveling in the blood may result in lower hormone levels in key cells that guide reproductive processes, leading to reduced maleness.

The researchers took into account differences between the subjects age, body mass index, smoking status, season of the year and the time of day that the blood samples were collected.

Even so, other factors might explain or contribute to the associations found in this study. Teasing out cause and effect is a challenge when studying humans rather then controlled animal studies in a laboratory.

Nonetheless, the findings coincide with what is know from animal studies and may be enough to convince some to limit vinyl products in their homes, offices, cars and kitchens.