Sperm cells carry traces of childhood stress decades later, scientists discover

Sperm cells carry traces of childhood stress, a new study has found.

The new research explored the “epigenetics” of sperm cells from fathers who had been exposed to stressful environments in childhood. Epigenetics is the study of how environmental factors can change the expression of genes without changing the DNA sequence. Epigenetic changes can be passed down from parent to child, and alter which genes are switched on.

Sperm cells from 58 fathers were analysed for the study, and most of whom were in their late 30s and early 40s. Researchers looked at two types of epigenetic markers: DNA methylation and small noncoding RNA.

DNA methylation is a chemical reaction and when DNA is methylated, the body can read this as a signal for how a gene is read. Small noncoding RNAs work in a similar way but rather than tagging the DNA molecule specifically, they can change the way the body reads RNA, a molecule that carries genetic information.

The research team found the participants through the University of Turku’s study of more than 4,000 families called the FinnBrain Birth Cohort that looks at how environmental and genetic factors influence a child’s development.

Traumatic events in childhood can alter sperm Getty Images

Childhood stress was measured using the Trauma and Distress Scale (TADS), an established questionnaire that asks about memories of emotional or physical neglect in addition to emotion, physical or sexual abuse. The TADS scores were then categorised as either being low (0 to 10), suggesting the participant remembered few stressful factors in childhood, or high (over 39), which meant they recalled many traumatic events.

Analysis of the results revealed that the sperm of men with high scores had a different epigenetic profile compared to the men who had lower scores. Researchers also found the same pattern after checking if the epigenetic differences could be attributed to other factors, such as drinking or smoking, which are also known to cause epigenetic changes that affect gene expression.

Lead study author Dr. Jetro Tuulari, an associate professor in the Department of Clinical Medicine at the University of Turku in Finland, said: “Epigenetics are basically saying which genes are active.

“Understanding inheritance through genes and DNA has been one of the most crucial elements of our understanding of biology,” Tuulari told Live Science. “We are now doing research that questions whether or not we have a complete picture.”

The results are “absolutely fascinating,” Tuulari said, because the stressors occurred early in the men’s lives but the epigenetic changes persisted over time, and decades since the events would have triggered them.

However, it is still early days for this field of research. Tuulari said researchers are working hard to find out more. It can’t be definitively stated that epigenetic changes can be passed from a human parent to their infant, however the findings from this study support this theory.

In other sperm-related news, mathematical scientists from Kyoto University in Japan revealed research suggesting that sperm can “defy the laws of physics” by not following Newton’s third law of motion. This law states that “for every action, there is an equal and opposite reaction.”

According to their research, the tails of sperm known as “flagella” have an “odd elastic” quality which makes them able to travel through viscous fluids without losing much energy.

They're able to propel themselves forward much easier than researchers would have predicted, seemingly avoiding coming into contact with an equal and opposite reaction.

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