The Invisible Legacy of Anxiety: How a Father's Stress Can Affect The Next Generation

A father's anxiety can influence the baby even before pregnancy occurs. Scientists have discovered that biological signals linked to male stress can alter embryonic development and even affect the growth of children years later.

For a long time, it was believed that only the mother's health and experiences during pregnancy influenced the baby's development. In recent years, however, scientists have been discovering that the father can also play an important role long before pregnancy occurs.

Now, a new study suggests that the stress and anxiety experienced by men can leave biological marks on sperm capable of influencing the development of future children.

The researchers focused on a small molecule called microRNA. Although it does not produce proteins, it functions as a kind of "biological switch," helping to control which genes will be activated or deactivated in cells.

Previous studies had already shown that a specific microRNA, called let-7f, appeared at higher levels in the sperm of men who reported higher levels of psychological stress. The big question was: could this alteration really affect the development of an embryo?

To investigate this, scientists used an experimental model with mice. In the laboratory, they collected embryos shortly after fertilization, when they were still just a single cell. Then, they performed an extremely delicate technique called microinjection, artificially introducing high quantities of let-7f into these embryos.

The goal was to reproduce the condition observed in men with higher stress levels. After that, the embryos were continuously monitored by imaging systems that recorded each stage of development, allowing researchers to observe in detail how they grew over time.

The results were unexpected. Initially, the embryos exposed to high levels of let-7f developed faster than normal. However, this accelerated growth seemed to come at a cost. Many of them encountered difficulties in later stages of development and showed lower survival rates.

To understand what was happening internally, the researchers analyzed which genes were being activated or deactivated in the embryonic cells. They discovered important alterations in genes linked to metabolism, body growth, and energy use, suggesting that the embryo was being biologically "programmed" differently from the first days of life.

Another finding was even more striking. The effects were not the same for males and females. The alterations appeared mainly in the male offspring.

When the offspring grew, the males that had been exposed to excess let-7f during the embryonic phase had greater body weight and longer bones than the animals in the control group. This suggests that a molecular alteration present at the time of conception can influence physical characteristics that remain throughout life.

The authors believe these findings help explain how experiences lived by fathers before pregnancy can be biologically transmitted to their children. This doesn't mean a father's anxiety will determine a child's future, but it reinforces the idea that male mental health is also part of reproductive health.

Although the study was conducted on mice and more research is needed to confirm the effects in humans, the results offer a new perspective on how emotions, stress, and environmental factors can influence the development of future generations in ways that science is only now beginning to understand.

READ MORE:

Elevated zygotic let-7f-5p alters developmental trajectories and sex-specific somatic growth

Lucas Y. Tian, Alyssa C. Jeng, Kerstin C. Creutzberg, Arthur S. Feltrin, Nickole Moon, Nicolae A. Leu, C. Neill Epperson, and Tracy L. Bale

iScience. Volume 29, Issue 6116115June 19, 2026

DOI:10.1016/j.isci.2026.116115

Abstract: 

Parental preconception experiences shape offspring development and longitudinal health outcomes, including disease risk. In a longitudinal human cohort, we previously identified sperm let-7f-5p (let-7f) as significantly increased in response to elevated prior perceived stress. As microRNAs (miRNAs) are causal agents in the germline transmission of prior paternal experience, we investigated developmental outcomes altered by increased let-7f using mouse zygote microinjection. Let-7f embryos developed at a faster rate until stalling at the morula stage, resulting in reduced blastocyst survival. Blastocyst and fetal RNA sequencing revealed significant differences in gene expression enriched for metabolic and growth pathways, effects that were limited to male offspring. Sex-specific developmental differences persisted into adulthood, with significantly increased body weight and bone length in let-7f males. These results demonstrate that increased let-7f shapes embryo development and male fetal and adult growth, advancing our understanding of how parental experiences may facilitate offspring developmental plasticity.