Be it animals or humans, stress is thought to be a part of life, but what if that started before birth?
A new study led by anthropology professor Zaneta Thayer ’08 has found that humans and other vertebrate species that are exposed to prenatal stress tend to produce higher stress hormones after birth. Emory University anthropology professor Adrian Jaeggi, Northwestern University doctoral candidate Andrew Kim, Thayer and University of Illinois Urbana-Champaign doctoral candidate Meredith Wilson conducted a meta-analysis on the effects of prenatal stress on stress hormone production in offspring. Their analysis, which was published in Scientific Reports, covered 114 results from 39 observational and experimental studies across 14 vertebrates.
The study focused on the hypothalamic pituitary adrenal axis across species, which is the physiological system that produces stress hormones in all vertebrates. The researchers tested the strength of the effect of prenatal stress on offspring hormone levels for a variety of characteristics, according to Thayer. These characteristics included sex of offspring, age of offspring, whether the species were mammals and other temporal factors relating to the gestation period.
The study found that the effect size was similar across species, which indicates that researchers may be able to study animals’ stress responses and apply those findings to human research. This is particularly beneficial for studying maternal stress in humans because of potential ethical complications that could arise from experimental tests conducted on humans, Wilson said.
“Being able to know that we can apply animal models, and that these animal models are actually representing something very similar that is happening in humans, is very important for future research,” Wilson said.
Additionally, the study found that experimental research designs showed stronger effects than purely observational studies. While observational studies sometimes offer a more “volatile approach,” they are often the only source of information available to researchers, according to Jaeggi.
The combination of these two main findings indicates that experimental studies of other vertebrates may be effective methods for researching prenatal stress and subsequent responses in humans, Wilson noted.
Kim said that this study provides “a more granular understanding of the severity of prenatal stress exposure and to what extent it is really going to impact the offspring.”
The study developed from Thayer’s ongoing interest in prenatal environments and how they influence offspring growth, development and later life health, she said. She worked on related projects while on Dartmouth’s anthropology foreign study program in New Zealand when she was an undergraduate at the College.
Existing literature on prenatal stress has historically interpreted stress hormones in offspring as an adaptive response where offspring’s increased stress hormones help them be vigilant and avoid predators, Thayer said. These increased stress hormones additionally increase risk for developing poor health outcomes later in life. Thayer described the “trade-off” between increased chances of survival and decreased immune, metabolic and reproductive functions as a result of stress hormones.
Thayer said she wanted to try “to understand whether this kind of pattern is consistent across species,” so she initially conducted a comprehensive evaluation of the literature with Kim and Wilson.
After seeing her present the results of her literature review at the annual American Anthropological Association in 2015, Jaeggi said he approached Thayer to suggest that her study could undertake more quantitative components and become an empirical meta-analysis.
The purpose of meta-analyses is “to survey and synthesize the state of a field,” Jaeggi said. He said he saw potential for Thayer’s study to quantitatively measure the strength of the effect of prenatal stress on offspring stress hormones and combine the effects from different studies into an overall measure.
Wilson said that in addition to yielding substantive results, the study also produced novel quantitative data and information about the function and feedback of the hypothalamus and pituitary and adrenal glands that researchers can use in the future.
Though the study shows generally positive effects of prenatal stress on offspring stress hormone levels, Jaeggi noted that more work is still necessary to evaluate the effect of prenatal stress on later life response.
Beyond the study’s evolutionary and biological implications, Thayer added that there is room for more research to be done on the factors that influence stress.
“What this kind of research suggests is that some individuals might be predisposed to developing poor health in adulthood based on stress experiences in their moms before they’re even born,” Thayer said.
She said that she is interested next in researching what factors may mitigate “the impact of stress on biology,” because not everyone experiences stress in the same way.
