Stress can have lasting impact on sperm and future offspring: Study

Prolonged fear and anxiety can not only take a toll on a person's mental health, but may also have a lasting impact on a man's sperm composition that could affect his future offspring, according to a study.

The research, published in the journal Nature Communications, outlines a biological mechanism for how a father's experience with stress can influence foetal brain development in the womb.

The effects of paternal stress can be transferred to offspring through changes in the extracellular vesicles that then interact with maturing sperm, said the researchers at the University of Maryland in the US.

Extracellular vesicles are small membrane-bound particles that transport proteins, lipids, and nucleic acids between cells, they said.

These vesicles are produced in large amounts in the reproductive tract and play an integral role in sperm maturation, researchers said.

"There are so many reasons that reducing stress is beneficial especially now when our stress levels are chronically elevated and will remain so for the next few months," said the study corresponding author Tracy Bale, Professor at the University of Maryland.

"Properly managing stress can not only improve mental health and other stress-related ailments, but it can also help reduce the potential lasting impact on the reproductive system that could impact future generations," Bale said.

To examine a novel biological role for extracellular vesicles in transferring dad's stress to sperm, the researchers examined extracellular vesicles from mice following treatment with the stress hormone corticosterone.

After treatment, the extracellular vesicles showed dramatic changes in their overall size as well as their protein and small RNA content.

When sperm were incubated with these previously "stressed" extracellular vesicles prior to fertilising an egg, the resulting mouse pups showed significant changes in patterns of early brain development, and as adults these mice were also significantly different than controls for how they responded to stress themselves.

To see if similar differences occurred in human sperm, the researchers recruited students from the University of Pennsylvania to donate sperm each month for six months, and complete questionnaires about their perceived stress state in the preceding month.

They found that students who had experienced elevated stress in months prior showed significant changes in the small RNA content of their sperm, while those who had no change in stress levels experienced little or no change.

These data confirm a very similar pattern found in the mouse study.

"Our study shows that the baby's brain develops differently if the father experienced a chronic period of stress before conception, but we still do not know the implications of these differences," said Bale.

"Could this prolonged higher level of stress raise the risk for mental health issues in future offspring, or could experiencing stress and managing it well help to promote stress resilience? We don't really know at this point, but our data highlight why further studies are necessary," she said.

The research team did find that stress-induced changes in the male reproductive system take place at least a month after the stress is attenuated and life has resumed its normal patterns.

"It appears the body's adaptation to stress is to return to a new baseline, a post-stress physiological state -- termed allostasis," Bale added.