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Sperm count dropping among French men and possibly elsewhere around the globe

Robin Wulffson MD's picture
sperm count, infertility, assisted reproduction, environmental factors

Mon Dieu! Frenchmen are becoming less fertile according to a new study. In addition, a decrease in the number of microscopic wigglers may be occurring in other regions of the globe. French researchers reported that between 1989 and 2005 the sperm count in an average 35-year-old Frenchman dropped by about 32%. They published their findings online on December 4 in the journal Human Reproduction.

The researchers evaluated the results of sperm samples from 26,609 partners of totally infertile women undergoing an assisted reproductive technology (ART) over a 17-year period. The men resided throughout France. They found a continuous decrease in semen concentration of about 1.9% per year and a significant decrease in the percentage with morphologically normal forms. The authors noted that a global decrease in human sperm quality is currently a topic subject to debate; however, geographical differences have been reported. In addition, a number of the studies comprised a small and/or biased sampling and statistical analysis was inappropriate. However, growing biological, toxicological, experimental, and human exposure data support the endocrine disruptors' hypothesis, which assumes that fetal exposure to endocrine disruptors could impair reproductive outcomes.

The investigators conducted a retrospective and descriptive study using data registered by Fivnat, the professional association in charge of statistics for ART in France during the 1989–2005 study period. The data was obtained from 126 main ART centers over the entire metropolitan territory of France. The study population included 154,712 men, aged 18–70, who were partners of couples undergoing their first ART cycle and for whom semen quality indicators (concentration, total motility and percentage of morphologically normal forms), measured on fresh ejaculated semen, were available.

The women had both fallopian tubes either absent or blocked. The temporal trends (change over time) for each indicator of semen quality were modeled using a generalized additive model that allowed for nonlinear relationships between variables and were adjusted for season and age. Variables such as fertility center, technique (standard in vitro fertilization or intra-cytoplasmic sperm injection), and an interaction factor between technique and time were also included in the model.

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The investigators found a significant and continuous decrease in sperm concentration of 32.2% during the study period. Projections indicate that concentration for a 35-year-old man went from an average of 73.6 million/ml in 1989 to 49.9 million/ml in 2005. A significant, but not quantifiable, decrease in the percentage of sperm with morphologically normal forms along the 17-year period was also observed. There was no global trend; however, a slight but significant increase in total motility between 1994 and 1998 was observed.

The researchers noted some limitations of the study. Socioeconomic status could not be controlled for. Despite universal access to medical services in France, couples undergoing ART are assumed to have a higher educational level on average compared with those of the general population. Therefore, the real values in the general population could be slightly lower than those found in the study. Thus, the decrease among the general population might be greater because, compared to the study population, the average Frenchman is more likely to smoke or be overweight, two factors known to impair semen quality.

The authors noted that the men were selected without any prior knowledge of their semen quality characteristics; therefore, the results are expected to be close to the values in the general French population. They wrote: β€œThe very large sample size and the robustness of the results confer great statistical power and credibility to the results. To our knowledge, it is the first study concluding a severe and general decrease in sperm concentration and morphology at the scale of a whole country over a substantial period. This constitutes a serious public health warning. The link with the environment particularly needs to be determined.”

Take home message:
Although this study was conducted in France, the findings are likely to be applicable to other developed nations including the United States. Environmental toxins are the most likely culprit. The reason the testicles are located outside the body cavity is because a lower temperature is required for sperm production. Men with undescended tests (cryptorchidism) are sterile. Long, hot baths can reduce sperm production. Men who work in a hot, steamy environment can also have a lower sperm count.

Reference: Human Reproduction

See also: Boys with undescended testes at increased risk for testicular cancer