Using epigenetic clocks in environmental epigenetics: recommendations for estimating biological aging in perinatal and pediatric samples

Following a variety of early environmental experiences and exposures, epigenetic modifications such as DNA methylation are proposed as candidate mechanisms that contribute to health and disease across the lifespan. Epigenetic clocks are a type of aging biomarker that can offer insight into age-related changes associated with early environmental exposures. This review provides a brief overview of epigenetic clocks that are readily available for use with perinatal and/or pediatric samples, as well as highlights some recent research that has studied the associations between early environmental chemical exposures and epigenetic aging rates. Broadly, the easily accessible epigenetic clocks can be categorized as chronological age estimators and gestational age estimators, but some clocks were developed for use with specific tissues and/or age groups. Previous environmental epidemiology studies have shown that early environmental exposures such as air pollutants and endocrine-disrupting chemicals are associated with altered epigenetic aging rates in perinatal and pediatric populations. However, more research is needed that examines how factors such as exposure level, timing of exposure, and sex may affect the direction and magnitude of associations. This review concludes with some recommendations and future directions for the use of epigenetic clocks in environmental epigenetics. Overall, epigenetic clocks are promising, non-causal biomarkers of early exposures that can be examined in relation to environmental chemicals, health and disease outcomes, and as biological mediators. Future research could help determine whether these clocks hold promise as informative biomarkers that reflect developmental epigenotoxicity following early exposure to environmental chemicals.