By Kelly A. Reynolds, MSPH, PhD
Efforts to track the quantity and quality of sperm in populations shows a steady decline in recent decades. Sperm counts worldwide have decreased by more than 50 percent and some fertility experts claim there is an epidemic of infertility. The phenomenon, however, is occurring most significantly in developed nations compared to the developing world. Although still controversial, associations with sperm-count decline and exposures to complex chemicals (i.e., plasticizers, pesticides, fire retardants, etc.) continue to be reported.
Sperm on a steady decline
“Why did American men lose 59.3 percent of their sperm?” This was the teaser headline for the August 12 broadcast of the internationally syndicated Michael Olson Food Chain Radio show with guest Irina Mindlis, MPH, co-author of a recent publication on the topic.1,2 A meta-analysis of sperm count and fertility trends reported in 185 studies with over 42K men from 1973-2011 was conducted. Results indicated that sperm counts declined significantly over the approximately 40-year span. Carlsen, et al., asked the same questions in 1992, following a review of 61 papers published between 1938 and 1991, including results from nearly 15K men that showed an overall decline in semen quality during the 50-year span.
In the more recent study, men were categorized geographically with those from western regions (i.e., North America, Europe, Australia, New Zealand) and those from other regions (i.e., South America, Asia and Africa). Those from the more developed western regions were marked by an average loss of 1.6 percent of total sperm counts per year—and still declining. The study found that total sperm count and concentration per mL of semen followed similar trends. In the first survey year, the average sperm count of western men was 99 million/mL compared to other regions averaging 73 million/mL and the last survey year at 47 million/mL and 62.6 million/mL, respectively. Sperm count is highly correlated with fertility and counts ranging below the 40 million/mL mark are associated with decreased probability of conception.3 In western men, sperm concentrations are less than half what they were in the 70s, with no sign of the trend leveling off, but there are no significant declines in men from South America, Asia and Africa.
Chemical interferences
While the recent sperm-decline study did not investigate potential causes of the results, environmental contaminants, such as endocrine disrupting compounds (EDCs) and pesticides, along with high-risk behaviors (such as smoking) have long been associated with low sperm counts. Saying something is associated with a health outcome does not mean it is proven. Other factors such as poor diet, stress and obesity also have negative impacts on both the quantity and quality of sperm. Determining which risk factor is driving the adverse outcome is a difficult task.
By definition, EDCs are chemicals or chemical compounds that can interfere with hormones in the body. The list of endocrine-disrupting compounds we are exposed to via, food, water and air is long, as they are commonly used compounds found in thousands of products. Exposures begin in the womb (continuing throughout our lifetime) but are generally found in very low levels where acute health effects do not occur. Exposures to low doses over long periods of time are difficult to assess as are the rather vague, suspected health effects, such as hormonal or developmental disorders.
In 2015, the Endocrine Society (a global group of academic researchers and physicians) issued a second scientific statement on EDCs, citing great research advances over the past five years leading to a better understanding of the adverse effects of common EDCs such as bisphenol A (BPA) and phthalates.4 BPA and phthalates are often used as plasticizers with the function of making plastics more pliable. Food containers and water bottles are two potential sources of exposure as the compounds can leach into the consumed contents, particularly when plastics are heated. Their individual human health effects at low-level exposures appears to also be acceptably low.
Previous studies in rats showed that high doses of phthalates resulted in adverse effects in reproductive biomarkers. Human exposure doses, however, tend to be low and chronic and humans are not rats. Thus, the question remains: what is the risk to humans? One study in humans looked at phthalate concentrations excreted in urine and correlated levels with sperm count and quality. Results indicated that increasing phthalate concentrations were significantly associated with lower total sperm counts, concentrations and quality as measured by head size and motility.5 The effects of phthalates on fertility were not established in the latter study and thus, the researchers caution against an over-interpretation of the results where confounding factors are likely.
Similarly, BPA doses in rats resulted in a wide range of adverse effects from cancer to abnormal sexual behavior to disrupted reproductive cycles. Studies in humans have indicated insufficient evidence for developmental and reproductive toxicity and minimal concern for low-level adult exposures but some concern for exposures to fetuses, infants and children.6 As a precautionary approach, however, industries and manufacturers began phasing out the use of BPA around 2006 in food and water storage containers with tax credit incentives from US EPA and the Food and Drug Administration.
Drinking water options
Given the paucity of data linking hormonal effects to plasticizers, many bottled water companies continue to use bottles containing BPA and phthalates. Data from the literature generally supports that bottled water is not a significant source of either of these compounds. They may contribute, however, to an additive effect along with other environmental sources. Because of these uncertainties, both sides of the issue passionately debate the next best step forward.7
Although definitive human health risks from phthalates and BPA have not been proven, many consumers are advocating for their removal from food and water. Avoiding these and other endocrine disrupting compounds in drinking water, may be difficult given that distribution piping and storage containers may contain a variety of suspect compounds. A resin code of seven on plastic containers indicates it may contain BPA. Consumers can self-select the types of bottles they choose to purchase if they are concerned about EDCs in packaging. Further, POU treatment of tap water with a properly installed and maintained NSF-certified water filter can decrease the levels of many EDCs, including phthalates and BPA.
References
- Michael Olson. Food Chain Radio: Men lost 59.3% of their sperm count… http://metrofarm.com/michael-olson/sperm-count-decline/. Accessed August 21, 2017.
- Levine H, Jørgensen N, Martino-Andrade A, et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update. 2017:1-14. doi:10.1093/humupd/dmx022.
- Bonde JPE, Ernst E, Jensen TK, et al. Relation between semen quality and fertility: a population-based study of 430 first-pregnancy planners. Lancet. 1998;352(9135):1172-1177. doi:10.1016/S0140-6736(97)10514-1.
- Gore AC, Chappell VA, Fenton SE, et al. Executive Summary to EDC-2: The Endocrine Society’s Second Scientific Statement on Endocrine-Disrupting Chemicals. Endocrine Reviews. 2015;36(6):593-602. doi:10.1210/er.2015-1093.
- Bloom MS, Whitcomb BW, Chen Z, Ye A, Kannan K, Buck Louis GM. Associations between urinary phthalate concentrations and semen quality parameters in a general population. Human Reproduction. 2015;30(11):2645-2657. doi:10.1093/humrep/dev219.
- National Toxicology Program, US Department of Health and Human Services. Monograph on the Potential Human Reproductive and Developmental Effects of Bisphenol A.; 2008.
- Cornwall W. In BPA safety war, a battle over evidence | Science | AAAS. Science (80- ). 2017:1. doi:09/02/2017.
About the author
Dr. Kelly A. Reynolds is an Associate Professor at the University of Arizona College of Public Health. She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at [email protected]