Infertility: New Scientific Results

Research in Denmark finds that low sperm counts in an earlier study was not the result of sexual immaturity in the study population. In 2000, a Danish study of young military recruits reported that many of them had low sperm counts, lower than earlier Danish measurements from prior decades. One explanation offered for this observation was the possibility that they were not yet sexually mature. This new study finds that sperm count of a subset of these young men did not increase as they were tracked over the next four years. Hence the low sperm counts are unlikely to be due to sexual immaturity. More...

Rats exposed in the womb to a single low dose of a widespread brominated flame retardant become hyperactive and have decreased sperm counts. The effects are observed at an exposure level within the range that has been found in samples of breast milk from US mothers. More...

Even at levels considered safe by the U.S. EPA, exposure very early in pregnancy to lawn care and farm chemicals resulted in serious developmental injury to mouse embryos. All but one of the 13 chemicals tested at very low doses on pre-implantation mouse embryos impaired normal development. All 6 mixtures tested caused damage. More... 23 August 2004

Gulf War veterans more likely to have fertility impairment. A large retrospective cohort study of UK veterans who served in the Gulf during the 1990-91 Gulf War finds a small increased risk of infertility and a longer time to conception compared to soldiers who did not serve in the Gulf. More... 3 August 2004

Risks of infertility higher in women using herbicides and fungicides. A study comparing infertile and fertile women in Wisconsin finds that women who were infertile were 27 times more likely to have mixed or applied herbicides in the two years prior to attempting conception than women who were fertile. The weight of animal and human evidence now clearly indicates that risks of infertility rise in association with current uses of agricultural chemicals. More...

Strong link established between pesticide exposure and reduced sperm quality in mid-West men. Research in the US mid-West has discovered that men with elevated exposures to alachlor, diazinon and atrazine are dramatically more likely to have reduced sperm quality. The study is the first to show such a link for common, current-use pesticides, and its findings are particularly troubling because the most likely route of exposure is through drinking water. The three pesticides implicated by the research are widespread contaminants in mid-West water systems. More...

New studies link environmental factors to impaired semen quality in men. Research in Denmark reveals a strong link between maternal smoking and a son's sperm concentration. Studies in Boston find higher phthalate and PCB levels in men with reduced sperm quality. A report from India also shows PCB and phthalate links. While none of these studies achieve scientific certainty about causation, they add to the weight of evidence that environmental factors are contributing to human infertility. Two invited commentaries published simultaneously in the scientific journal, Epidemiology,—one about phthalates, one about sperm count— place these new research results in a broader context. 25 May 2003.

Many spontaneous miscarriages and birth defects in people, including Down Syndrome, are caused by an error in cell division called aneuploidy. After an accident in two of the world's leading laboratories investigating aneuploidy caused a dramatic increase in this chromosomal error in the labs' mice, careful study revealed that it had been caused by inadvertent contamination by the plastic molecule bisphenol A (BPA). Subsequent work, published today as the cover story in Current Biology, then demonstrated that even very low levels of bisphenol A interfered with cell division.

BPA is the plastic monomer used to make polycarbonate plastic (the sort of rigid plastic from which baby bottles can be made, and large (not small) water bottles, including one variety being sold wholesale to health food stores because "it doesn't leach plasticizers." BPA is widely used to make a resin that lines food cans. Experiments show that BPA readily leaches out of this resin into the food within the cans.

These results open a new window into understanding the cause of human birth defects, and significantly heighten pressure to reduce human exposures to bisphenol A. 31 March 2003. More...

Research in Sweden reveals a link between organochlorine levels in a mother's blood and the risk that her son will develop testicular cancer, decades after birth. The son's own contamination levels, measured at the time of cancer diagnosis, provide few insights into risk. What matters is what the developing fetus experienced in the womb. These data are consistent with the proposal that testicular cancer in adulthood results from errors in fetal testicular development caused by hormone disruption. 26 December 2002. More...

11 November 2002. In the most sophisticated study of geographic variation in US sperm count yet conducted, scientists from four different geographic regions across America report they find important differences in sperm density and motility. Men in Missouri have the lowest sperm count compared to New York, Minneapolis and Los Angeles. The cause of these differences are not yet known. The scientists conducting the study hypothesize it may be related to the intensity of pesticide use in industrial agriculture in Missouri compared to the other, more urban areas. More...

14 October 2002. Russian male pesticide workers exposed to dioxin and dioxin-like compounds father fewer boys than would be expected on the basis of world-wide and regional sex ratios. Normally slightly more boys are born than girls, with a resulting sex ratio (# boys divided by # of total births) averaging 0.51. In Ufa, a town just west of the Urals where pesticides have been produced since the 1940s, the sex ratio of children born to exposed fathers was 0.38, and that of a highly exposed subgroup was 0.23. More...

17 September 2002. Research conducted at the University of Wisconsin reveals that a commercial mixture of lawn chemical herbicides including 2,4-D causes fetal loss in mice. A story about this research in the LA Times reports that the scientists who conducted the study obtained the herbicides by simply going to a local hardware store and buying a common brand.

Tests are usually conducted on pure components of such brands, instead of the actual mixtures sold. Tests with the pure components had indicated exposure at levels used in these experiments should not have caused effects. In fact, the lowest level used in the experiments, which caused significant fetal loss, was one-seventh the level allowed by EPA in drinking water.

These results indicate that mixtures must become a focus of regulatory testing for toxicology, and that current standards are not adequate. More...

8 August 2002. Danish scientists combine information from several different sources to challenge the conventional demographic interpretation of why fertility rates are falling in industrialized countries. In a paper published in the scientific journal Human Reproduction, they propose that the decline may not be due solely to voluntary choices made by women about how many children they should have. In addition, they argue that involuntary factors may also be involved, specifically the increasing percentage of men whose sperm density is sufficiently low to impair fertility. More...