Environmental factors in declining human fertility

• Published in: Nature reviews. Endocrinology Vol. 18; no. 3; pp. 139 - 157
• Main Authors: Skakkebæk, Niels E., Lindahl-Jacobsen, Rune, Levine, Hagai, Andersson, Anna-Maria, Jørgensen, Niels, Main, Katharina M., Lidegaard, Øjvind, Priskorn, Lærke, Holmboe, Stine A., Bräuner, Elvira V., Almstrup, Kristian, Franca, Luiz R., Znaor, Ariana, Kortenkamp, Andreas, Hart, Roger J., Juul, Anders
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2022; Nature Publishing Group
• Subjects: 631/443/494/2732/2730; 692/163; Endocrinology; Environmental factors; Female; Fertility; Fossil fuels; Health problems; Humans; Infertility; Infertility - epidemiology; Infertility - etiology; Interdisciplinary research; Male; Medicine; Medicine & Public Health; Population decline; Pregnancy; Reproduction; Reproductive behavior; Reproductive health; Review Article; Semen Analysis; Testicular cancer; Testicular Neoplasms - complications; Testicular Neoplasms - epidemiology; Trends
• ISSN: 1759-5029; 1759-5037
• DOI: 10.1038/s41574-021-00598-8

A severe decline in child births has occurred over the past half century, which will lead to considerable population declines, particularly in industrialized regions. A crucial question is whether this decline can be explained by economic and behavioural factors alone, as suggested by demographic reports, or to what degree biological factors are also involved. Here, we discuss data suggesting that human reproductive health is deteriorating in industrialized regions. Widespread infertility and the need for assisted reproduction due to poor semen quality and/or oocyte failure are now major health issues. Other indicators of declining reproductive health include a worldwide increasing incidence in testicular cancer among young men and alterations in twinning frequency. There is also evidence of a parallel decline in rates of legal abortions, revealing a deterioration in total conception rates. Subtle alterations in fertility rates were already visible around 1900, and most industrialized regions now have rates below levels required to sustain their populations. We hypothesize that these reproductive health problems are partially linked to increasing human exposures to chemicals originating directly or indirectly from fossil fuels. If the current infertility epidemic is indeed linked to such exposures, decisive regulatory action underpinned by unconventional, interdisciplinary research collaborations will be needed to reverse the trends. This article discusses trends in human reproductive behaviour and health that are associated with infertility. These changes have occurred over a period of only a couple of generations, so environmental factors are suggested to have a role. Key points Industrialized regions have birth rates so low that their populations cannot be sustained; declines in birth rates are generally ascribed to socioeconomic and cultural factors, although human infertility is widespread. Decreasing fertility rates were already recorded around 1900 in Denmark, a few decades after the beginning of utilization of fossil fuels that were, and still are, drivers of modern industrialization and wealth. We hypothesize that declines in fertility rates might be linked to exposures to chemicals originating from fossil fuels causing human reproductive problems and cancer; early gestation might be a sensitive period. The current unsustainable birth rates will eventually result in decreasing populations. A key research challenge remains: how to distinguish biological from socioeconomic and behavioural factors?