Contrasting with earlier studies, new research from Sweden1 suggests that men exposed to phthalates (THAL-ates)—chemical plasticizers that are commonly used in household products and certain medical items—don't have a higher risk of becoming infertile.
The study, from Lund University Hospital in Lund, Sweden, was published in the July issue of the journal Epidemiology.
Ubiquitous Substance
Phthalates are synthetic chemicals used in plastics and other consumer products. People are exposed to these chemicals through breathing, ingestion, and skin contact.2 Much of the products in which phthalates are used are made of polyvinyl chloride (PVC), such as in pipes, to help increase flexibility and durability. Other products include food packaging, clothing, toys, blood bags, IV fluid bags, and other medical devices.
Phthalates are also used to hold color and scent in certain fragrances and soaps, as carpet backing, and as solvents in paints, glue and insect repellents.3
While studies have suggested the chemicals are cancer-causing in laboratory animals, "the extent of these toxicities and their applicability to humans remains incompletely characterized and controversial," experts write.4
Possible Link to Male Infertility Studied
The Swedish researchers, led by Bosse A.G. Jonsson, PhD, in the department of Occupational and Environmental Medicine, noted that previous research had suggested exposure to phthalates could be detrimental to male fertility,5,6 which prompted them to initiate this study in hopes of coming up with more answers.
"Urine, [blood], and semen samples were collected from 234 young Swedish men at the time of their medical conscript examination," Jonsson and his colleagues wrote.
The investigators then measured semen volume, sperm concentration levels and how quickly the sperm were able to move (motility), along with several other tests, such as sperm chromatin integrity, a measure of the amount of normal DNA and protein in the head of the sperm.
In the blood samples they collected, Jonsson and his team measured levels of reproductive hormones. And in the urine samples, they measured levels of four different kinds of phthalates.
One Weak Association Found
In the end, the researchers found no relation between levels of mono butyl phthalate, mono benzyl phthalate, and mono ethylhexyl phthalate in any of the reproductive measurements they took.
They did notice that in men with higher levels of mono ethyl phthalate, sperm motility was reduced, as were levels of luteinizing hormone (LH), a hormone that plays a role in sperm production in the testes, "but there was no suggestion of harmful effects" in this weak association, they wrote.
In conclusion, the study authors wrote that the evidence about the link between phthalate exposure and male infertility is still questionable. "The observed weak associations between one phthalate [level] and impairment of a few aspects of reproductive function [measurements] were not consistent with results from a recent U.S. study," they wrote. "It is not yet possible to conclude whether phthalate exposure may reflect a hazard for human male reproduction."
Jonsson says he and his fellow researchers next plan to study the impact of phthalate exposure on fertility in another group of men in hopes of helping set the record straight.
Increased Infertility Risk Found Elsewhere
In a study published two years ago,4 doctors at the Harvard School of Public Health looked for any link between phthalate levels and reproductive problems in men. They enrolled nearly 170 men who were undergoing semen analysis for infertility at an area hospital for the study. The patients were compared with men who had normal reproductive function.
Sperm concentration, motility, and morphology (sperm structure) were all measured in each group of men, as well as levels of phthalates in urine samples.
The researchers found that the higher the levels of mono-butyl phthalate, the lower the sperm motility and sperm concentration, though the latter association was not found to be significant. Higher levels of mono-benzyl phthalate were also associated with lower sperm concentration.
There was also "suggestive evidence" that monomethyl phthalate exposure may negatively impact sperm morphology, though that association wasn't conclusive. No other phthalate levels were linked with reproductive dysfunction in the patients. That may be due to "a difference in [sperm toxicity] among phthalates," the study investigators theorized.
1. Jonsson BA, Richthoff J, Rylander L, Giwercman A, Hagmar L. Urinary phthalate metabolites and biomarkers of reproductive function in young men. Epidemiology 2005 Jul;16(4):487-93.
2. Latini G. Monitoring phthalate exposure in humans. Clin Chem Acta 2005 Jul 5;[Epub ahead of print].
3. Duty SM, Singh NP, Silva MJ et al. The relationship between environmental exposures to phthalates and DNA damage in human sperm using the neutral comet assay. Env Health Perspect 2003 Jul;111(9):1164-9.
4. Shea KM, American Academy of Pediatrics Committee on Environmental Health. Pediatrics 2003 Jun;111(6 Pt 1):1467-74.
5. Duty SM, Silva MJ, Barr DB et al. Phthalate exposure and human semen parameters. Epidemiology 2003 May;14(3):269-77.
6. Veeramachaneni DN. Deteriorating trends in male reproduction: idiopathic or environmental? Anim Reprod Sci 2000 Jul 2;60-61:121-30.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
