India’s Reproductive, Maternal, Newborn, Child and Adolescent Health (RMNCH+A) programme has steadily reduced maternal mortality, neonatal deaths, and childhood mortality over the past three decades. Success is undeniable, when measured by survival. Yet, a quieter concern is surfacing in clinics and epidemiological data. Many children appear more vulnerable to recurrent infections, metabolic disturbances, and reduced physical robustness. The question is no longer about survival alone, but also about the biological quality of that survival. Increasingly, scientists are beginning to suspect that something fundamental may be missing in how we understand the inheritance of traits from parents.

Missing fathers

Reproductive health within the health system has traditionally focused almost exclusively on mothers. Antenatal care, maternal nutrition, and institutional deliveries form the core of national programmes. Fathers, in contrast, have largely remained outside the biological narrative. Emerging scientific evidence now suggests that this omission may not be trivial. A father’s diet, lifestyle, exposure to toxins, stress and environment -- long before conception -- may influence the biology of the child in ways we are only beginning to understand. This shifts the conversation we need to have from a mother-centric model to a more inclusive, bi-parental understanding of health transmission.

What changed

The traditional model of reproduction is straightforward. The ovum contributes maternal genetic material, and the sperm delivers the paternal genome. The fusion of these two forms is a zygote, which develops under the guidance of DNA. In this framework, the father’s role is limited to the transmission of DNA. His lifestyle choices (including whether he exercised, smoked, or lived in polluted surroundings) were believed to have no bearing on what was passed on. For over a century, this model was reinforced by August Weismann’s idea of the blood-testis barrier, which held that environmental influences cannot affect germ (sperm and egg) cells. According to this view, a man’s lifestyle, whether healthy or harmful, would not influence the sperm in a way that could be passed on to the next generation. The sperm was seen as a passive carrier of DNA, insulated from the external environment.

This assumption began to weaken in the early 2010s, when studies demonstrated that paternal exposures such as poor diet, alcohol consumption, and environmental toxins could influence offspring traits. These traits were not encoded in DNA changes, but appeared to be transmitted through epigenetic mechanisms. Small molecules, particularly RNA fragments in sperm, were identified as carriers of such information. These molecules could regulate gene expression in early embryos, effectively transmitting information about the father’s environment without altering the genetic code itself. This discovery marked a shift in biology, suggesting that inheritance is more dynamic than previously believed. However, one key question remained unanswered: how exactly are these signals transmitted, and how do they shape the child’s biology?

New evidence

A recent study published in Cell Metabolism by Chinese researchers adds an important layer to this evolving story. In this study, male mice that underwent structured treadmill exercise for eight weeks produced offspring with significantly improved endurance and metabolic profiles. Quantitatively, these offspring ran longer and covered greater distances in treadmill tests, with statistically significant differences often exceeding 30%-40% compared to offspring of sedentary fathers. Oxygen consumption measurements showed higher VO2 levels across light and dark cycles, indicating enhanced metabolic efficiency. Muscle analysis revealed a shift towards oxidative fibre types, with a notable increase in type I and type IIa fibres and a reduction in glycolytic fibres.

The most compelling contribution of the study lies in its proposed mechanism. The researchers demonstrate that paternal exercise alters the profile of sperm microRNAs, a class of small non-coding RNAs. These microRNAs are delivered to the oocyte at fertilisation and interact with early embryonic transcripts. The study suggests that microRNAs suppress nuclear receptor corepressor 1, a molecule that normally inhibits PGC-1α, a master regulator of mitochondrial function. By relieving this inhibition, the embryo is programmed towards enhanced oxidative metabolism and mitochondrial development. The study further strengthens this causal pathway by injecting sperm-derived small RNAs from exercised fathers into normal embryos, which then reproduced similar metabolic and endurance phenotypes in offspring. It suggests that these RNA molecules are not merely markers, but active agents of inheritance.

Permeating the barrier

One of the most intriguing implications concerns how these molecular signals bypass the classical Weismann barrier. The study suggests that systemic physiological states, such as increased muscular PGC-1α activity during exercise, can influence the composition of small RNAs in sperm. While the exact transport mechanism remains unclear, it is hypothesised that circulating RNA fragments or vesicle-mediated transport systems may allow signals from somatic tissues to influence germ cells. In effect, the barrier is not absolute but selectively permeable to regulatory molecules, particularly small RNAs that can re-programme gene expression without altering DNA.

During fertilisation, the sperm does more than deliver DNA. It contributes a complex molecular cargo, including proteins and RNA fragments. These molecules interact with the oocyte cytoplasm and influence the earliest stages of embryonic development.

The study highlights that sperm microRNAs can act immediately after fertilisation, modifying transcriptional networks before the embryo begins its own gene expression. This early window appears critical, as small changes in gene regulation at this stage can lead to lasting physiological differences in the offspring.

What we still don’t know

Several uncertainties persist. The precise fate of these microRNAs after fertilisation is not fully understood. It remains unclear how long they persist, which genes they consistently target, and whether their effects extend beyond the first generation. Furthermore, the findings are based entirely on animal models, and extrapolation to humans must be done cautiously. Human reproductive biology is more complex, and environmental exposures are far more variable. There is also a limited understanding of dose-response relationships, that is, how much lifestyle change is required to produce measurable effects in offspring.

What needs to be done

Even though we still don’t fully understand how a father’s lifestyle influences his child’s biology, what is increasingly clear is that it does. This understanding however, is yet to translate into policy action. In India, under the RMNCH+A program, male involvement remains limited to the supplementation of iron tablets to adolescent boys. There is no structured focus on paternal preconception health, no systematic screening for lifestyle risks among prospective fathers, and minimal emphasis on environmental exposures that may affect sperm quality.

Addressing lifestyle factors such as physical activity, substance use, and environmental exposures among men of reproductive age may offer a low-cost, high-impact strategy to improve population health across generations. If these findings hold true in humans, the implications are profound.

(Dr. C. Aravinda is an academic and public health physician. The views expressed are personal. aravindaaiimsjr10@hotmail.com)