Impact of changes in human reproduction on the incidence of endocrine-related diseases

Abstract

The incidence rates of a wide range of diseases and conditions have increased over the last decades. There is controversy over the origin of these increases, whether they are caused by exposure to compounds thought to have an effect on the endocrine system, the “endocrine disruption theory”, or whether some other factor is responsible. In this analysis, the authors take a closer look at the role that changes in reproductive factors have played in this respect. They apply the relative risks of age at first pregnancy and parity or family size to a set of Dutch demographic data from 1955 and 2015 and calculate the percentage of disease increase explained. The decrease in parity over the last decades explains an increase of 26% in testicular cancer. The combination of decrease in parity and increase in maternal age at first pregnancy explains an increase of 34% in hypospadias prevalence. This combination of decreased parity and increased maternal age at pregnancy explains an increase of 24% in childhood obesity prevalence. The authors further point to a perhaps even more profound effect of the trend toward smaller families. This trend has led to an estimated doubling of the proportion of children born from subfertile couples. Since children born from subfertile couples are more likely to be preterm or of low birth weight, the incidence of these conditions must have increased as well. Low birth weight and preterm delivery are risk factors for a wide range of diseases and conditions. The changes in human reproduction over the last decades have had a profound impact on the incidence of a range of diseases and conditions in the next generation and thus provide a sound explanation for a substantial portion of the reported increases.

Key messages

• The incidence rates of a wide range of diseases and conditions have increased in the Western societies over the last decades.

• Many have argued that these increases are attributable to compounds thought to have effects on the human endocrine system: the endocrine disruption theory

• This analysis shows, however, that human reproductive factors such as maternal age at first pregnancy and parity explain substantial proportions of the reported increases

Keywords:

• Endocrine disruption
• risk factors
• reproductive factors
• demography
• subfertility
• testicular cancer
• hypospadias
• childhood obesity and epidemiology

Acknowledgments

The authors gratefully acknowledge the reviewers for their comments on the manuscript. Their comments and suggestions were helpful to us and contributed to the clarity and accuracy of our publication. But most of all we are grateful for the inspiring words of one of the reviewers who remarked that our piece of work gave some serious food for thought on the endocrine disruption controversy.

Declaration of interest

The authors declare to have no conflict of interest. No funding was received for this project. This critical review was conducted during the normal course of the authors’ employment using institutional funding. No outside funds were used to prepare the review. The review is the professional work product of the authors and the views expressed are not necessarily the views of their employers. None of the authors have appeared during the last five years in any regulatory or legal proceedings related to the contents of this paper.