Our Stolen Futurea book by Theo Colborn, Dianne Dumanoski, and John Peterson Myers



posted 19 November 2006

Hauser, R, JD Meeker, S Duty, MJ Silva and AM Calafat 2006. Altered Semen Quality in Relation to Urinary Concentrations of Phthalate Monoester and Oxidative Metabolites. Epidemiology 17: 682–691.

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Consistent with prior findings by this Harvard research team, men with higher levels of a metabolite of the phthalate DBP have lower sperm concentration and mobility, low enough to be beneath levels considered by the World Health Organization to be unhealthy. Exposures were not excessive, but instead within the range experienced by many people.

Context: Human sperm quality varies significantly among men and among places; there is also evidence, albeit not conclusively that sperm quality has declined significantly over time. In some regions, for example northern Europe, a surprisingly high proportion of young adult men have suboptimal sperm quality.

The patterns and time in space that have been found in human sperm quality variation indicate environmental factors are probably involved, particularly as experiments with animals have shown sperm quality is affected by environmental contaminants that are widely distributed. Hence epidemiologists have designed studies to test for associations between chemical exposures and sperm quality.

Most animal experiments examining impacts of phthalates on sperm quality have focused on developmental exposures: how exposures during pregnancy affect offspring once adult. These consistently show an impact of exposure to the parent compounds DBP, BBzB and DEHP. Some have looked at the effects of exposure during adulthood, and there is some evidence that at relatively high levels, adult exposure to DBP, BBzP, and DEHP can be harmful to the testes.

The current study examined the relationship between current exposure levels in adulthood and sperm quality. Because phthalates are rapidly metabolized and excreted, the measurements they obtained of contamination levels will largely reflect exposure during the day of measurement.

What did they do? Over a 5 yr period, Hauser et al. obtained sperm and urine samples from 463 men who had come from a hospital for infertility treatment.

They determined the levels of metabolites of four phthalates, listed to the right:

[common uses of these phthalates]

Phthalate table

They then analyzed relationships between phthalate metabolites and several aspects of sperm quality: sperm concentration, motility, and morphology.

What did they find? Hauser et al. found a statistically significant relationship between MBP levels and sperm motility and sperm concentration: men with high MPB had lower sperm quality (p <0.04 for both sperm parameters). Sperm morphology showed no trend.

MBP and sperm concentration  

The odds ratios for impaired (below WHO reference level) sperm concentration (above) and impaired sperm motility (below) both increased at higher MBP levels. Men in the highest quartile of MBP levels were 3.3 times more likely to have lower sperm concentration than men in the lowest quartile.

Q1- Q4 are quartiles 1 through 4
Red horizontal line is odds ratio = 1.0.
Black vertical lines show 95% confidence intervals.

MBP and sperm motility

No strong associations were seen for any of the other phthalate metabolites, although the data for MBzP suggested a trend (p = 0.13).

Because gathering the data for this study took place over 5 calender years, Hauser et al. were able to look for trends in the concentration of metabolites. They observed that while MEHP increased, MMP decreased; others showed no trends.

What does it mean? Exposure to dibutyl phthalate, as measured by detection of DBP's metabolite, MBP, is associated with an increased risk of impaired sperm quality, at levels of MBP present in the general population.

These results are consistent with earlier work on MBP by this research team with a smaller sample size. That earlier study had also reported a stronger association between poor sperm quality and three other metabolites, MBzP, MMP and MEP.

The results are also consistent with laboratory studies with rodents showing that DBP is toxic to the testes. Those studies also show that DEHP has adverse effects on testes. No association was found in this research between DEHP metabolites and impaired sperm quality.

Hauser et al. also discuss how their work differs from a Swedish study that found no association with MBP. Men in the Swedish sample were younger and drawn from the general population, not patients at an infertility clinic. Hauser et al. used assays that were much more sensitive than the Swedish studies, so that detection limits in the Swedish study were manyfold higher than in this one.





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