Falling sperm counts and changes to sexual development are “threatening human survival” and leading to a fertility crisis, a leading epidemiologist has warned. Writing in a new book, Shanna Swan, an environmental and reproductive epidemiologist at Icahn School of Medicine at Mount Sinai in New York, warns that the impending fertility crisis poses a global threat comparable to that of the climate crisis. “The current state of reproductive affairs can’t continue much longer without threatening human survival,” she writes in Count Down. It comes after a study she co-authored in 2017 found that sperm counts in the west had plummeted by 59% between 1973 and 2011, making headlines globally. Now, Swan says, following current projections, the median sperm count is set to reach zero in 2045. “That’s a little concerning, to say the least,” she told Axios. In the book, Swan and co-author Stacey Colino explore how modern life is threatening sperm counts, changing male and female reproductive development and endangering human life. It points to lifestyle and chemical exposures that are changing and threatening human sexual development and fertility. Such is the gravity of the threats they pose, she argues, that humans could become an endangered species. “Of five possible criteria for what makes a species endangered,” Swan writes, “only one needs to be met; the current state of affairs for humans meets at least three.” Swan offers advice on how to protect themselves from damaging chemicals and urges people to “do what we can to safeguard our fertility, the fate of mankind, and the planet”. Between 1964 and 2018 the global fertility rate fell from 5.06 births per woman to 2.4. Now approximately half the world’s countries have fertility rates below 2.1, the population replacement level. While contraception, cultural shifts and the cost of having children are likely to be contributing factors, Swan warns of indicators that suggest there are also biological reasons – including increasing miscarriage rates, more genital abnormalities among boys and earlier puberty for girls. Swan blames “everywhere chemicals”, found in plastics, cosmetics and pesticides, that affect endocrines such as phthalates and bisphenol-A. “Chemicals in our environment and unhealthy lifestyle practices in our modern world are disrupting our hormonal balance, causing various degrees of reproductive havoc,” she writes. She also said factors such as tobacco smoking, marijuana and growing obesity play a role.
This article originally appeared in The Guardian of February 26, 2021.
Levine H, Jørgensen N, Martino-Andrade A, Mendiola J, Weksler-Derri D, Mindlis I, Pinotti R, Swan SH. (2017). Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update. 23, 646–659.
Swan SH, Colino S. (2021). Count Down: How our Modern World Is Threatening Sperm Counts, Altering Male and Female Reproductive Development, and Imperiling the Future of the Human Race. Scribner, NY, USA.
Dr. Swan has worked for over twenty-five years to understand the threats posed by chemicals to our environment and our health, and, when necessary, to develop new paradigms to assess their risks. Of most concern to Dr. Swan are the chemicals that our bodies can confuse with its own hormones (the “endocrine disrupting” chemicals). At the Icahn School of Medicine at Mount Sinai, Department of Environmental Medicine and Public Health, Dr. Swan is working with a wide range of collaborators, including epidemiologists, biostatisticians, toxicologists, geneticists and systems biologists, to conduct studies and develop methods to evaluate the risks from such chemicals ‒ methods that are sensitive enough to tease out the often subtle health effects of complex mixtures.