Gene expression is influenced by a surprisingly wide range of factors, from molecular switches inside your cells to the food you eat, the stress you experience, and even the time of day. Your DNA contains roughly 20,000 genes, but not all of them are active at once. The process of turning genes on and off, or dialing their activity up and down, is what determines everything from how your cells develop to how your body responds to illness.
Transcription Factors: The Master Switches
The most direct influence on gene expression comes from proteins called transcription factors. These molecules bind to specific stretches of DNA near a gene and either recruit the cellular machinery needed to read that gene or block it from being read. Think of them as switches that can flip a gene into an “on” or “off” position.
For a gene to be read, a large assembly of proteins must come together at the gene’s starting point, called the promoter. This assembly includes the enzyme that copies DNA into RNA, along with a mediator complex that acts as a bridge between transcription factors and the rest of the copying machinery. Some transcription factors bind to enhancer regions, which can sit thousands of DNA letters away from the gene itself. The DNA physically loops to bring these distant enhancers close to the promoter, which is necessary for the gene to be successfully activated.
Epigenetic Modifications: Changes Above the DNA
Your genes don’t exist as naked strands of DNA. They’re wrapped tightly around protein spools called histones, and the whole structure is packed into a dense material called chromatin. How tightly that chromatin is packed determines whether a gene can be reached and read. Two major chemical modifications control this packaging: DNA methylation and histone acetylation.
DNA methylation involves adding a small chemical tag (a methyl group) directly to the DNA. When methyl tags accumulate near a gene’s promoter, the surrounding chromatin becomes more tightly packed and resistant to being unwound. Activator proteins that could normally access DNA and switch on a gene can no longer reach their binding sites once that DNA has been methylated and assembled into this condensed state. Methylation is responsible for silencing genes on the inactive X chromosome in females, for genomic imprinting (where only the copy from one parent is active), and for shutting down tumor-suppressor genes in many cancers.
Histone acetylation works in the opposite direction. Adding acetyl groups to the tails of histone proteins weakens their grip on DNA. This loosens the chromatin and makes the underlying genes accessible to transcription factors. Heavily acetylated regions of the genome tend to be transcriptionally active, while regions with low acetylation are typically silent. The interplay between these two systems, methylation tightening things down and acetylation opening things up, provides a finely tuned volume dial for gene activity.
One critical feature of epigenetic modifications is that they are often reversible. Unlike mutations, which permanently alter the DNA sequence, methylation and acetylation patterns can be added or removed by specialized enzymes. This reversibility is what makes lifestyle interventions like diet and exercise capable of reshaping gene expression over time.
Non-Coding RNAs: Post-Transcriptional Fine-Tuning
Even after a gene has been read and copied into an RNA message, its expression can still be dialed down. Small RNA molecules called microRNAs, only about 20 to 24 genetic letters long, are estimated to regulate roughly 50% of all genes. They work by pairing with messenger RNA molecules and either blocking them from being translated into proteins or marking them for destruction. This gives cells a rapid way to adjust protein production without changing anything at the DNA level.
Longer non-coding RNAs, defined as those exceeding 200 genetic letters, play different roles. Some remodel chromatin structure, effectively changing which genes are accessible. Others control where transcription factors end up inside the cell. For instance, one long non-coding RNA prevents a key immune signaling protein from entering the nucleus, keeping it inactive until the right stimulus arrives. Together, these RNA-based systems add layers of control that operate after the initial decision to read a gene has already been made.
Diet and Nutrient-Gene Interactions
What you eat directly influences which genes are active. Dietary cholesterol, for example, suppresses the gene responsible for making the enzyme your liver uses to produce its own cholesterol. Polyunsaturated fatty acids from foods like fish and nuts reduce the RNA output of fat-producing enzymes in liver cells, with the effect varying based on how unsaturated those fatty acids are.
Some food compounds alter gene expression through epigenetic pathways. Sulforaphane, found in broccoli and other cruciferous vegetables, inhibits an enzyme that removes acetyl groups from histones. The result is increased acetylation near the promoters of genes involved in cellular aging and programmed cell death, effectively turning those protective genes up. Butyrate, produced when gut bacteria ferment dietary fiber, and diallyl disulfide from garlic work through a similar mechanism.
Folate plays a particularly well-studied role. It’s essential for maintaining normal DNA methylation patterns. People who carry a common genetic variant in the MTHFR gene, which is involved in folate metabolism, are more vulnerable to disrupted methylation and elevated blood levels of the amino acid homocysteine, especially when their dietary folate intake is low. This gene-nutrient interaction has been linked to increased risk of colorectal and cervical cancers.
Environmental Chemicals and Toxins
Certain synthetic chemicals alter gene expression by mimicking hormones or directly interfering with epigenetic machinery. Endocrine-disrupting chemicals can bind to hormone receptors inside cells and either modify the enzymes that control histone and DNA methylation or act as rogue transcription factors, switching on genes that should remain quiet.
Bisphenol A (BPA), found in some plastics and food packaging, has been linked to altered DNA methylation patterns in children exposed during fetal development, with associations to behavioral abnormalities. In animal studies, BPA exposure during pregnancy affected methylation across multiple generations, producing reproductive, neurological, metabolic, and cardiac problems in offspring and even in the generation after that. Phthalates, common in plasticizers and personal care products, have been shown to reduce testosterone production in rodents through changes in both histone modifications and DNA methylation. Dioxins alter gene expression through multiple epigenetic pathways simultaneously, affecting histone modifications, DNA methylation, the enzymes that manage those marks, and microRNA levels.
Polycyclic aromatic hydrocarbons, released by burning fuel and cooking at high temperatures, have been associated with DNA methylation changes and chromosomal damage in adult human blood cells. Even formaldehyde, a common industrial chemical, has been linked to methylation changes over a lifetime of exposure.
Stress and the Immune System
Psychological stress reshapes gene expression, particularly in the immune system. Acute, short-lived stress tends to boost resistance to infection, but chronic stress does the opposite. Prolonged stress reduces the expression of cortisol receptors in the brain, which impairs the body’s ability to regulate its own stress response, creating a feedback loop.
A study of over 1,200 people living in socioeconomically disadvantaged neighborhoods found altered DNA methylation in both stress-related and inflammation-related genes across multiple types of immune cells, including B cells, T cells, and natural killer cells. Chronic stress also drives changes in histone modifications. In animal models, sustained psychological stress altered histone packaging near genes that control gut barrier function and ramped up production of an inflammatory signaling molecule, contributing to increased pain sensitivity. These findings illustrate how your environment and psychological state physically rewrite the chemical marks on your genome.
Exercise and Muscle Gene Activity
A single bout of endurance exercise triggers pronounced changes in gene expression in skeletal muscle. In one study, researchers took muscle biopsies before and immediately after exercise and found that the three most strongly activated genes in the working muscle all belonged to a family involved in metabolism and cell growth. But the effects weren’t limited to the muscles doing the work. In the resting, non-exercising leg, genes related to fat metabolism signaling were also upregulated, suggesting that exercise sends systemic signals, likely through the bloodstream, that influence gene activity body-wide.
Over time, regular physical activity is one of the most studied and broadly accepted strategies for modifying epigenetic patterns associated with aging. Exercise-related epigenetic changes are thought to contribute to its well-documented effects on metabolic health, inflammation, and disease risk.
Your Internal Clock
Gene expression follows a roughly 24-hour cycle driven by your circadian clock. In every cell of your body, a feedback loop runs continuously: a pair of proteins (CLOCK and BMAL1 in mammals) activates a set of clock genes. The proteins produced by those genes gradually accumulate and then travel back to the nucleus, where they shut down the very proteins that activated them. This cycle takes about 24 hours to complete, and it’s present in nearly every cell type.
Light keeps this internal clock synchronized with the outside world. When light hits specialized cells in your eyes, a signal reaches the brain’s master clock, where it triggers calcium to flow into neurons. This activates a protein that binds to the promoters of core clock genes and resets their expression timing. The result is that thousands of downstream genes, controlling everything from hormone release to DNA repair, follow a predictable daily rhythm. Disrupting this rhythm through shift work, jet lag, or nighttime light exposure throws off the timing of gene expression throughout the body.
Can These Changes Pass to Your Children?
Whether environmentally caused changes in gene expression can be inherited across generations remains one of the most debated questions in biology. Animal studies provide compelling evidence that they can. In mice, exposure to traffic-related air pollution during pregnancy produced altered DNA methylation patterns not only in the offspring, but in the grandchildren and great-grandchildren, none of whom were directly exposed.
The mechanism likely involves small regulatory RNAs and certain methylation marks that escape the normal “reset” process that wipes most epigenetic marks clean during early embryonic development. Imprinted genes, which are only expressed from one parent’s copy, demonstrate that some methylation signals do survive this reprogramming. Histone modifications may also pass directly through the maternal side.
In humans, the picture is less clear. Studies have documented intergenerational effects, such as grandparental smoking being associated with increased asthma and allergy risk in grandchildren. But definitive proof of true transgenerational epigenetic inheritance in humans, where effects persist in a generation that was never directly exposed to the original trigger, is still lacking. The majority of the DNA methylation landscape is reprogrammed during embryonic development, which acts as a barrier to this kind of inheritance. Animal models suggest the barrier is leaky, but confirming this in people remains a major challenge.