Male Reproductive Health Declines

Rising rates of testicular cancer, more frequent genital defects, and deteriorating sperm quality indicate that male reproductive health is declining in many populations. Between 1960 and 2002, closely monitored men in Europe, the United States, and New Zealand became two to seven times more likely to suffer from testicular cancer (see Table 1) and, on average, produced about half as many sperm per milliliter of semen.1 These changes have yet to be adequately explained, but their rapid onset among younger men suggests environmental disruptions during early development are at least partly to blame.

Testicular cancer afflicts less than 1 percent of the population, but it has become the most common malignancy among men ages 20 to 34.2 The rate of testicular cancer among men under 50 across northern Europe, Australia, New Zealand, and the United States has been increasing about 2–4 percent a year since the 1960s.3 Since rates of cryptorchidism (undescended testicles) and hypospadias (shortened urinary tracts) have risen simultaneously, some specialists have identified a broader “testicular dysgenesis syndrome” that threatens male fertility.4 Men born with testicular deformities and survivors of testicular cancer tend to have more problems producing enough healthy sperm to conceive children.5

The most recent analysis of several dozen studies conducted primarily in Europe, North America, and Australia since the 1930s found that sperm density has fallen from 110–170 sperm per milliliter to just under 60.6 Studies demonstrating such a broadly based decline in sperm counts have been controversial, however, because sperm quality can vary widely over the course of a man’s life—rising during periods of abstinence, for example, and declining during the summer.7 Study samples have also often come from men seeking vasectomies (who tend to have higher than average sperm counts) or from men in couples experiencing infertility (who tend to have lower than average).8

Yet there is a consensus that sperm counts vary by region and have fallen more in some places than others. Men in New York City have sperm counts 75 percent higher than men in Columbia, Missouri, for example, while men in Turku, Finland, have counts 25 percent higher than men in Copenhagen, Denmark.9 Although just one sperm is required to fertilize an egg, researchers have identified sperm concentrations of 40 per milliliter of semen as the threshold below which men’s fertility declines.10 According to a 2006 analysis, about 40 percent of men from Denmark and Norway are below this level.11

In the United States, testicular cancer is most common among urbanites in the northwestern and central states and less likely in New England and the South.12 In Europe, the incidence is greatest in the region encompassing Denmark and Switzerland and lowest in the Baltic states, France, Italy, and Spain.13 In some cases this inter-regional difference is sharp: men born in Denmark or Norway are three times as likely to have testicular cancer as men born in Estonia or Finland.14

Some populations may be genetically more vulnerable to reproductive disruption than others. Testicular cancer is five times less common among African Americans, for example, while European men, on average, have higher sperm counts than American or Japanese men.15 But such differences do not explain the degree of geographic variation in reproductive maladies: although they are closely related in genetic backgrounds, men in Denmark have notably lower sperm counts that men in southern Sweden.16

Some lifestyle choices affect sperm counts. Men who drink more alcohol or smoke more cigarettes tend to have lower sperm counts.17 Overweightness, age, and other drug use have also been associated with lower sperm quality.18 Cell phones may inhibit healthy sperm production: a 2007 study found that men in Cleveland, New Orleans, and Mumbai who used cell phones longer than four hours each day had sperm counts 25 percent lower than those who never used them.19 Yet this relationship may be confounded by other variables, such as sedentary living.20

Exposure to chemicals that interfere with sex hormones remains the prevailing explanation for the increase in male reproductive disorders.21 Scientists have identified more than 50 synthetic chemicals that disrupt the endocrine system and more than a dozen additional suspects.22 Those most firmly associated with reproductive disorders include dioxins, which are released during paper pulp processing, coal combustion, and waste incineration; polychlorinated biphenyls, which are used for a range of electrical, insulation, lubrication, and other industrial purposes; and pesticides that are commonly used in agriculture.23

Phthalates—a common plastic softener— have also been linked with reproductive maladies. 24 A 2006 study in China found that workers exposed to phthalates while manufacturing polyvinyl chloride materials had lower levels of testosterone.25 In a broader Massachusetts study, men with higher levels of phthalate metabolites in their blood had lower sperm counts, lower sperm motility, and more sperm deformities.26

Many compounds known to be disruptive to reproductive development have been banned— but only after years of widespread use. Between 1950 and 1975, for example, doctors prescribed the estrogen-mimic diethylstilbestrol to 5 million pregnant women, hoping to promote fetal growth and prevent spontaneous abortions.27 Two decades passed before researchers realized the sons of these women were more likely to have smaller testicles, genital deformities, and impaired sperm quality.28

Today more than 80,000 synthetic chemicals are in production, and most have unknown long-term effects.29 Acknowledging this, in 1996 the U.S. Environmental Protection Agency initiated an Endocrine Disruption Screening Program to evaluate more than 15,000 chemicals. 30 In Europe, similar concerns culminated in the 2005 Prague Declaration on Endocrine Disruption, which was signed by hundreds of scientists from Europe and North America. It warned of “serious risks” to men’s fertility and urged more comprehensive monitoring of male reproductive maladies.31

Clouding researchers’ ability to identify harmful chemicals is the potential for some chemicals to be safe in isolation but dangerous in tandem with others. A 2006 study of tadpoles found that only 4 percent died when they were exposed to each of nine common pesticides alone but 35 percent died from exposure to a mixture of all nine.32 Since each person on Earth now contains detectable levels of several hundred synthetic chemicals, in varying proportions, it is impossible to identify all the potentially toxic chemical cocktails. Accordingly, the Prague Declaration called for a “precautionary approach” to regulating potentially disruptive chemicals—an appeal to err on the side of caution even in the absence of scientific consensus about the sources of endocrine disruption.33