Imagine receiving a book at birth. It contains instructions for how the body can be built and how it functions. If you have an identical twin, you have both received essentially the same genetic book — the same DNA sequence.
But a book is more than the letters on its pages. It also matters which sections can be read, when they are used, and in which tissue. That is where epigenetics comes in. The image is a simplification, but it helps us distinguish between the DNA text itself and the biological markings that influence how genetic information is handled.
Can exercise change these markings and thereby how our genes work? Research is investigating this question, but the verified twin study behind this article gives a more cautious answer than the headline might suggest.
Quick answer
Can exercise change how your genes work?
Exercise does not rewrite your DNA sequence, but research is investigating whether it may influence how certain genes are expressed through epigenetic changes. A verified twin study found that leisure-time activity had at most a minor effect on the studied DNA methylation age measure. The findings call for caution before broad claims.
Key takeaways
- Exercise does not rewrite your DNA sequence and does not give you new genes.
- Epigenetics covers biological mechanisms, including DNA methylation, that influence how genetic information is regulated and read.
- The verified study examined DNA methylation age in younger and older Finnish twins, as well as long-term activity-discordant older twin pairs.
- Active and inactive co-twins showed no clear difference in the studied methylation age measure; leisure-time physical activity in adulthood was judged to have at most a minor effect on its acceleration.
- The study does not show that exercise slows or reverses ageing and does not support broad claims about inflammation, metabolism, or disease.
Wait — can exercise really affect genes?
Not by rewriting the DNA sequence. A training session does not swap letters in your genetic code, give you new genes, or make you genetically "upgraded".
What researchers can study is how cells regulate the use of genetic information. Another metaphor applies here: think of DNA as a piano. The keys are there, but biology determines which notes can be played in a particular cell at a particular time.
The metaphor is not a mechanical description of the body. It simply shows why the same DNA sequence does not mean all genes are used in exactly the same way everywhere or throughout life.
What is epigenetics?
Epigenetics concerns biological mechanisms that can influence how genetic information is organised and read without the DNA sequence needing to change. DNA methylation is one such mechanism.
In this study, a particular measure called DNA methylation age was used. It is calculated from methylation at selected sites in DNA and compared with chronological age. The difference between the two is often called acceleration in DNA methylation age.
This is a research measure, not a complete verdict on how old or healthy a person is. The researchers themselves emphasised that it is not established whether the epigenetic clock drives ageing or primarily reflects other processes.
Why twins are particularly interesting for epigenetics
Identical twins share essentially the same DNA sequence. When researchers compare them, they can therefore examine how genetic and non-shared environmental factors contribute to variation in an epigenetic measure.
The study included both identical and fraternal twins in younger and older groups. The researchers also used a co-twin analysis of older same-sex pairs who had reported clearly different levels of leisure-time physical activity over 32 years.
The twin design is powerful, but it does not turn daily life into a perfect experiment. Activity was measured through reports and interviews, and the twins may have differed in more ways than just movement.
What the research actually shows
In the older twin group, non-shared environmental factors explained a larger share of the variation in DNA methylation age acceleration than in the younger group. Genetic factors nevertheless still explained a substantial portion of the variation.
When researchers compared the long-term more and less active co-twins, they observed no clear difference in DNA methylation age. The average measure lay close to chronological age in both groups, and the uncertainty interval included no difference.
The younger twin cohort gave the same overall picture: the analysed activity measures were not linked to acceleration in DNA methylation age. The authors' conclusion was therefore that leisure-time physical activity in adulthood had at most a minor effect on this particular measure.
What the research does not show
The study does not show that exercise reverses ageing. Nor does it show that physical activity makes a person biologically younger according to all conceivable measures.
It did not analyse whether exercise "activates" genes for fat burning, inflammation, insulin sensitivity, or disease protection. Such topics require their own verified mechanistic sources and cannot be derived from this twin study.
The absence of an association for one particular epigenetic clock does not simultaneously mean physical activity has no other effects. It means this particular study did not find the clear link with DNA methylation age that the hypothesis predicted.
Exercise, lifestyle, and gene expression
Epigenetics and gene expression are broad research fields. Physical activity can be studied in relation to many molecular processes, but results depend on tissue, training mode, timing, measurement method, and population.
This article therefore stays with a cautious formulation: lifestyle factors may be linked to biological regulation, but the verified primary source does not show that leisure-time physical activity in adults clearly changes the studied epigenetic clock.
Claims about inflammation, metabolism, insulin, or specific gene expression remain as possible subjects for future articles once additional primary sources have been verified.
Are our genes our destiny?
Genes are important for our biological predispositions, but they are not a complete account of a life. In the study, contributions from genetic and non-shared environmental factors varied between younger and older twin groups.
That does not mean every lifestyle choice leaves a simple and measurable epigenetic signature. It means biological variation can be shaped by multiple layers simultaneously — genes, environment, age, random processes, and things science cannot yet fully measure.
The book of DNA remains. But understanding how it is read is considerably more complicated than saying a particular habit opens a particular page.
What does this mean for twins?
Twins give us an unusual opportunity to see how similar genetic starting points can meet different lives. But the similarity does not make one twin a control group for every everyday choice the other makes.
If you and your twin exercise differently, the study does not say who is ageing "best". Nor does it give a test result that can be used as a personal prognosis.
The most useful thing is curiosity: the same DNA can coexist with biological variation, and every new research measure needs to be examined for what it actually measures.
The TwinPare perspective
At TwinPare we like the book and the piano because they make a difficult idea understandable. But good metaphors need brakes. Exercise does not rewrite the book, and research has not shown that a particular training session automatically picks the right page or key.
The exciting question lies in the more honest version: how do genes, environment, and life interact over time? Twin research helps us investigate that question without pretending a single study already has the whole answer.
You cannot choose your DNA sequence. But you are also not reducible to it. Between those two thoughts lies a large and still-growing field of research.
Source and limitations
The source supports that both genetic and non-shared environmental factors contributed to variation in acceleration of DNA methylation age, and that the environmental share was larger in the older than in the younger twin group.
The source does not support the idea that exercise changes the DNA sequence, reverses ageing, or clearly lowers the studied epigenetic age. In the long-term activity-discordant pairs, no clear difference was seen between more and less active co-twins.
The co-twin analysis was small: seven identical and nine fraternal pairs. Activity was based on reported and interviewed data, and DNA methylation age is a specific biomarker measure with its own methodological limitations.
The study is still valuable for TwinPare readers because it shows both the strength of the twin design and why appealing headlines about genes and ageing need to be tested against the actual result.
Source notes
The source has been verified and editorially reviewed for this article. The limitations below show which level of conclusion the sources support.
- [sillanpaa-2019] Leisure-time physical activity and DNA methylation age-a twin study. Elina Sillanpää; Miina Ollikainen; Jaakko Kaprio; Xiaoling Wang; Tuija Leskinen; Urho M. Kujala; Timo Törmäkangas. Clinical Epigenetics, 2019. Evidence type: Twin cohort and co-twin control analysis of DNA methylation age, including younger and older Finnish twins and 16 long-term activity-discordant older pairs Limitation: The study examined a specific DNA methylation-based age measure. In the co-twin analysis of seven identical and nine fraternal pairs, no clear difference was observed between active and inactive co-twins. The authors concluded that leisure-time physical activity in adulthood had at most a minor effect on acceleration in this measure. PubMed PMC DOI
Editorial source review
This section shows how the article's key factual claims are linked to the source.
Phrasings that require caution
- Write that exercise does not change the DNA sequence; epigenetics is not a rewriting of the genetic code.
- Call DNA methylation age a specific research measure, not a complete or definitive biological age.
- Write that the study found no clear co-twin difference and at most a minor effect of leisure-time physical activity in adulthood on acceleration of the measure.
- Do not claim that exercise reverses ageing, activates particular genes, or changes genes linked to disease.
- Do not link inflammation, metabolism, insulin sensitivity, or gene expression to the primary source without additional verified sources.
- Explain that the book and piano metaphors are pedagogical simplifications, not literal biological mechanisms.
| ID | Claim | Source support | Caution |
|---|---|---|---|
| C1 | Physical activity does not change a person's DNA sequence; the study instead examined DNA methylation as an epigenetic measure. | 2019 | Always distinguish DNA sequence from epigenetic regulation and avoid phrasing that implies exercise rewrites genes. |
| C2 | The study used Horvath's DNA methylation age and analysed the difference between this measure and chronological age. | 2019 | Call it a specific biomarker-based research measure, not a definitive biological age. |
| C3 | The co-twin analysis included seven identical and nine fraternal pairs with long-term differences in reported activity levels. | 2019 | Mention the small sample and that the analysis did not consist exclusively of identical twins. |
| C4 | In the activity-discordant co-twin analysis, no statistically clear difference in DNA methylation age was observed between active and inactive co-twins. | 2019 | Describe the absence of a clear difference and do not reframe the result as a hidden positive training effect claim. |
| C5 | The authors concluded that leisure-time physical activity in adulthood had at most a minor effect on acceleration in DNA methylation age. | 2019 | Tie the phrasing to this specific methylation age measure, not to ageing or health in general. |
| C6 | Both genetic and non-shared environmental factors contributed to variation in acceleration of DNA methylation age. | 2019 | Do not translate population-level variance into a claim about what drives an individual twin's biological future. |
| C7 | The study gives a cautious result on a specific epigenetic age measure and cannot carry broad health or ageing claims. | 2019 | Keep the limitation visible near the conclusion and before the source notes. |