What Is Epigenetics?

Genes play a fundamental role in shaping human health, yet they do not work in isolation. Daily behaviors and environmental factors — such as diet, physical activity, and exposure to external conditions — also contribute significantly to how the body functions. The field of epigenetics examines how lifestyle choices and environmental influences can modify gene activity without altering the underlying DNA sequence. These modifications, unlike permanent genetic mutations, are reversible and influence the way genetic instructions are interpreted.

Gene expression describes the process by which instructions encoded in DNA are translated into proteins. While genetic mutations can alter the actual proteins produced, epigenetic modifications control whether specific genes are active (“on”) or inactive (“off”). Because factors like nutrition, stress, and exercise can lead to epigenetic adjustments, researchers often emphasize the strong link between an individual’s environment, behavior, and genetic regulation.

Mechanisms of Epigenetic Regulation

Epigenetic processes control gene expression through several mechanisms:

DNA Methylation
One of the most studied mechanisms is DNA methylation, in which chemical groups are attached to specific sites on the DNA strand. These groups can block the binding of proteins that normally “read” the gene. As a result, methylation typically silences a gene, while demethylation removes the chemical marks, allowing the gene to be activated.

Histone Modification
DNA does not float freely inside the nucleus; instead, it coils around proteins called histones. The way histones are packed affects gene accessibility. When histones are tightly packed, DNA is less available to be read, and the gene is effectively turned “off.” Conversely, loosely packed histones expose DNA, enabling gene activity. Chemical tags can be added or removed to regulate how tightly the DNA wraps around histones, thereby controlling gene activity.

Non-Coding RNA
While some RNA molecules carry instructions to produce proteins, others — non-coding RNAs — play a regulatory role. These molecules can attach to messenger RNA (mRNA), preventing it from being translated into proteins. Non-coding RNAs can also recruit proteins to histones, altering their configuration and switching genes “on” or “off.”

Epigenetics Across the Human Lifespan

Epigenetic changes begin even before birth and continue throughout life, influenced by natural development as well as by environmental conditions and personal habits.

Epigenetics in Development
Although every cell in the human body carries the same DNA, cells take on distinct roles — becoming skin, nerve, or muscle cells — through epigenetic regulation. For example, a muscle cell activates genes required for contraction while silencing genes specific to nerve function. This selective gene expression enables cells to specialize and perform their unique roles.

Epigenetics and Aging
Epigenetic patterns shift over time. A study comparing DNA methylation in a newborn, a 26-year-old, and a 103-year-old showed clear age-related differences: methylation was highest in the newborn and lowest in the centenarian. These findings suggest that age contributes to gradual, measurable changes in the epigenome.

Reversibility of Epigenetic Changes
Importantly, not all epigenetic marks are permanent. Behaviors and environmental shifts can sometimes reverse changes. For instance, smoking alters DNA methylation at certain sites in the AHRR gene, with heavy smokers showing the strongest effects. Remarkably, quitting smoking can restore methylation levels, sometimes within a year, although the speed of recovery depends on the duration and intensity of smoking habits.

Epigenetics and Human Health

Because epigenetic regulation is dynamic, it can influence both disease development and disease prevention.

Infections
Pathogens may manipulate host epigenetics to weaken immunity. For example, Mycobacterium tuberculosis, the bacterium responsible for tuberculosis, can alter histone structures in immune cells, shutting down the IL-12B gene and thereby suppressing immune responses.

Cancer
Cancer development is closely tied to both genetic mutations and epigenetic disruptions. A well-known example involves the BRCA1 gene: mutations in this gene heighten breast cancer risk, but so can excessive DNA methylation that reduces BRCA1 expression. Cancer cells typically exhibit abnormal methylation — either too much at certain sites or globally reduced levels. These patterns vary between cancer types and can even help doctors identify subtypes or detect hidden cancers through screening. In colorectal cancer, for instance, methylation changes in specific DNA regions are detected through stool-based screening tests, though abnormal results still require confirmation via colonoscopy.

Nutrition During Pregnancy
Maternal behaviors during pregnancy can also shape a child’s epigenome. A mother’s diet and environment may leave long-lasting epigenetic marks on the fetus, potentially influencing the child’s health risks decades later.