Environmental and lifestyle factors are damaging men's reproductive health and may be playing a large role in decreasing fertility rates in industrialized countries, a new study in Physiological Reviews reports. Socioeconomic influences and female reproductive health cannot solely be blamed for higher incidences of infertility, the study supports.
A team of experts in reproductive medicine from Denmark, Finland and the U.S. reviewed the available population and animal studies on reproductive health, examining incidences of testicular cancer and male organ development disorders, testosterone level, sperm quality, ratio of male-to-female children born, frequency of childlessness and demand for assisted reproductive techniques. The researchers examined factors that could affect reproductive health: gene mutations, which are changes in the gene caused by alterations in the DNA code; gene polymorphisms, which are variations of the same gene; epigenetic changes, the alteration of the gene due to changes in how the DNA code is read; and environmental and modern lifestyle factors, including exposure to chemicals, occurrence of traumatic events, fitness and nutrition.
The analysis showed that poor semen quality contributed to increases in infertility and use of assisted reproductive technology. It also revealed higher incidences of testicular cancer worldwide with the greatest frequency in countries with Caucasian populations. Lower levels of testosterone in men and increased occurrence of congenital abnormalities of reproductive organs in male newborns were also observed.
"I was surprised that we found such poor semen quality among young men ages 20 to 25," says lead researcher Niels Skakkebaek of the University of Copenhagen in Denmark. "We found that the average man had more than 90 percent abnormal sperm. Normally, there would be so many sperms that a few abnormal ones would not affect fertility. However, it appears that we are at a tipping point in industrialized countries where poor semen quality is so widespread that we must suspect that it results in low pregnancy rates."
Many of the male reproductive problems could be detected in utero. While the reproductive problems could arise from genetic changes, "recent evidence suggests that most often it is related to environmental exposures of the fetal testis," the researcher team wrote.
"Since the disorders in male genitals are increasing in a relatively short period of time, genetics cannot explain this development," Skakkebaek says. "There is no doubt that environmental factors are playing a role and that endocrine [hormone]-disrupting chemicals, which have the same effect on animals, are under great suspicion. The exposure that young people are subjected to today can determine not only their own, but also their children's, ability to procreate."
According to Skakkebaek, the study has significant public health implications. "Governments in industrialized countries seem much more interested in the current economic aspects of low birth rates and do not see the writing on the wall for the long-term environmental effects on our population's ability to reproduce.
"I am also surprised that the media still subscribe to the idea that low fertility rates are a result of socio-economic factors and do not make the connection between subfertility and the booming in vitro fertilization industry, which suggests a role of infertility," Skakkebaek says. "The only biological factor that currently comes up in the media and in demographic papers is the role of the age of delivering women. Age does indeed play a role. However, the situation is more complex. We found in our analysis that the average age of a delivering woman in Denmark in 1901 was the same as today, suggesting that delayed childbearing alone cannot explain the current trends."
More research in reproductive medicine needs to be done to understand and address the declining fertility rates, according to Skakkebaek. "If socioeconomic factors alone were behind the current trends, they could be reversed by political measures. On the other hand, if our populations have become less fertile or more people even have become infertile, it is a much bigger problem for our societies. Only biomedical research can identify and solve the problems."
American Physiological Society