Grandparents' exposure to environmental chemicals could influence their granddaughters' first menstruation

A study links the age of menarche with the exposure of grandparents and parents to environmental pollutants that disrupt the endocrine system, demonstrating the intergenerational transmission of these environmental risks to reproductive health.

In recent decades, there has been a global advance in the age of puberty in girls (between one and two years since the beginning of the 20th century), as well as in the age of the milestones that define it, namely the onset of thelarche (breast budding) and menarche (first menstruation). This advance may have important implications in later stages of life, increasing the likelihood of mental health problems, cardiometabolic diseases and even cancer.

Although there is no single reason behind this advance, the research group led by Dr Barbara Cohn of the Berkeley Public Health Institute in California suggests that exposure to environmental chemicals capable of disrupting the endocrine system (Endocrine Disrupting Chemicals, EDCs) may be behind earlier puberty.

The researchers used data from the ‘Study of Child Health and Development,’ a prospective birth cohort of pregnant women that began in the 1960s, who were followed along with their daughters (247 girls, born around 1963) and granddaughters (139 girls, born around 1990).

They measured exposure to different environmental pollutants in blood samples collected from the three generations. Specifically, they looked at 250 pairs (parents) from the first generation, 247 daughters from the second generation, and 139 granddaughters from the third generation. The results showed that, although the age of menarche remained stable between the first and second generations, it was brought forward by a full year in the third generation, and that this advance was associated with certain endocrine-disrupting chemicals present in the blood of both mothers and fathers.

This research highlights the importance of reducing exposure to endocrine-disrupting chemicals during conception and pregnancy, but above all the lasting impact of these environmental exposures on reproductive health across generations.

The study adds another point of interest that has not been sufficiently addressed until now: the relevance of paternal exposure and not just that of the mother who conceives. The researchers observed, for example, that exposure to phenoxyethanol, a common preservative in personal hygiene products and also in food, was associated with earlier puberty when both parents had been exposed, but the influence of the father was even greater.

This is therefore one of the first population studies to highlight the role of paternal and grandpaternal exposures in the reproductive development of their daughters and granddaughters, supporting the role of epigenetic inheritance.

In recent years, various experimental studies have indicated that exposure to certain toxic compounds (pesticides, industrial chemicals, etc.) could underlie the phenomenon of a reduction in the average age of menarche or first menstruation. In this context, although most studies published to date have focused on direct or maternal exposure, the summary of the work presented at the annual meeting of the Endocrine Society in San Francisco (USA) goes further and provides new evidence on the intergenerational impact of these environmental exposures.

Using advanced metabolomics techniques, which allow for the mass analysis of metabolites present in biological samples, this research identifies complex associations between certain blood markers—especially in grandparents and parents—and earlier puberty in their daughters and granddaughters. Thus, the observed reduction of a full year in the average age of menarche among daughters and granddaughters could reinforce the hypothesis that environmental factors not only affect those who are directly exposed, but can also be transmitted and amplified in future generations, possibly through epigenetic mechanisms. The results also highlight the influence of the male lineage in the transmission of endocrine risks to female offspring, as well as the role played in this process by key metabolites such as tryptophan, fumarate and succinate.

Pending the publication of the full study, in order to thoroughly assess the methodology and reliability of the results and, therefore, their strengths and limitations, it can be said that these results open a promising avenue for future research on women's health and inherited environmental exposures. This molecular approach complements previous theories of environmental and socio-genetic transmission by focusing on specific metabolic pathways. Furthermore, exploration of this interesting field of research could have important implications for public health policies in relation to the alarming current exposure to endocrine disruptors that the scientific community has been warning about in recent decades.

The press release presents the main findings of the study in a clear and accessible manner, making it easy to understand for a general audience. It includes statements from the authors of the study, who highlight the novel contribution of this research regarding the importance of the male lineage in the intergenerational transmission of endocrine risks.