NEW YORK (Reuters Health) - Contrary to earlier reports, phthalates -- plasticizers used extensively in household and medical products -- may not have significant adverse effects on reproductive function in young men, according to a report in the July issue of Epidemiology.

Previous studies suggested that low levels of phthalate could adversely affect human semen parameters, the authors explain, but high doses of phthalates are required to provoke male reproductive toxicity in rodents.

Dr. Bosse A.G. Jonsson from Lund University Hospital, Sweden, and colleagues investigated any association between phthalate metabolite levels in urine, semen quality and reproductive hormone parameters in 234 young Swedish men entering military service.

There were no associations between any of the phthalate metabolites and any of the reproductive biomarkers, the authors report.

Men with the highest quartile of phthalate metabolite levels had larger testis volume, fewer motile sperm, more immotile sperm, and lower luteinizing hormone values, the report indicates, but "there was no suggestion of harmful effects for most other endpoints."

The results differed, however, for phthalic acid, which seemed to be linked to improved reproductive function. Men with the highest phthalic acid levels had larger testis volume, more motile sperm, and fewer immotile sperm than men with the lowest phthalic acid levels.

"The results showed some weak associations between phthalate biomarkers in urine and reproductive function biomarkers," the researchers conclude. "This pattern may reflect a hazard for male reproduction from phthalate exposure, but the results also may be spurious."

"I do not think it is clear whether phthalate constitutes a risk for the male fertility," Dr. Jonsson told Reuters Health. "More studies must be performed."

"We plan to study biological samples stored in biobanks from pregnant mothers and study the fertility in their grown-up male children," Dr. Jonsson added.

Epidemiology 2005;16:487-493.

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