In a study of the possible association between phthalate exposure and human semen quality, researchers at the School of Public Health’s (SPH) Occupational Health Program have found an association between select phthalates and low sperm count, low sperm motility, and an increased percent of abnormally shaped sperm among a group of men from couples seeking treatment at a fertility clinic in Boston. Low sperm count, low motility, and abnormal sperm morphology can affect the likelihood of conception but do not mean that a man is infertile.
Dividing the group into thirds based on their levels of phthalate exposure as measured in a urine sample, the researchers found that the third with the highest levels of monobutyl phthalate and monobenzyl phthalate were three to five times more likely to have a low sperm count or low sperm motility than men in the lowest third of exposure. Men with the highest levels of monomethyl phthalate were more likely to have a higher percentage of abnormally shaped sperm.
Phthalates are a class of compounds used to hold color and scent in many cosmetics and personal care items such as soaps, detergents, skin preparations and aftershave lotions, and they also find their way into food during processing and through packaging materials. One phthalate, di-2-(ethylhexyl) phthalate, is used to soften a wide range of plastic products, which includes medical devices. Phthalates are also present in drinking water and residential indoor air.
The study appears in the May 2003 issue of Epidemiology, http://www.epidem.com.
Several commonly used industrial chemicals, including phthalates, have been associated with reproductive toxicity in laboratory animals. This toxicity is of concern because a large proportion of the general U.S. population is exposed to phthalates. Furthermore, several researchers have found declining sperm counts in developing countries and have hypothesized that industrial chemicals could be partly responsible.
Federal studies, such as the National Health and Nutritional Examination Survey (NHANES), a study on the health and diets of the U.S. population, conducted by the Centers for Disease Control and Prevention (CDC), have found several phthalates present in more than 75 percent of subjects sampled. Researchers from the CDC are collaborating with SPH researchers and performed the phthalate analyses for the SPH study.
The researchers, led by Susan M. Duty and Russ Hauser of SPH, have termed the study preliminary, as it evaluated semen quality and a single urine sample from a limited number of subjects, 168 men at an infertility clinic associated with the Vincent Memorial Obstetrics and Gynecology Service, Massachusetts General Hospital. The researchers plan follow-up studies with larger groups of men to confirm the results. In addition, they also plan to incorporate additional tests to measure semen quality. If the results are confirmed, their next step would be to explore whether men differ in their sensitivity to these compounds.