Wednesday March 7 2012
Research says exercise affects DNA but does not change its code
“Just a few minutes of relatively strenuous exercise can dramatically change a person’s DNA,” according to the Daily Mail. The newspaper said new research has found that 20 minutes of exercise can “crank up the genes needed to burn fat and sugar and support the body”.
Exercise is known to affect the energy-making machinery in cells and alter how the body processes sugar. The study examined whether exercise might do this by making a particular type of change to DNA. DNA contains genes, which act as the blueprints for making various proteins, including those involved in releasing energy.
The researchers thought that a process called DNA methylation could be involved. This process influences whether, and to what extent, the body "switches on" genes in our DNA. To test the hypothesis, the researchers asked healthy young people who did not regularly exercise to complete a single, intense cycling session. They tested DNA methylation in samples of thigh muscle taken before and after the exercise. They found that after exercise, the amount of DNA with methylation had decreased, and concluded that this may be the process by which muscle adapts to exercise. However, the changes seen appeared to be only temporary.
It is important to note that this study did not find that exercise changes people’s underlying genetic code (the sequence of "letters" that make up our DNA).
Exercise has numerous benefits for health and weight, which are explained in our health and fitness section.
Where did the story come from?
The study was carried out by researchers from the Karolinska Institute in Sweden, the University of Copenhagen and Dublin City University. The research was funded by the European Research Council, European Foundation for the Study of Diabetes and other institutions throughout Europe and Australia.
The study was published in the peer-reviewed scientific journal Cell Metabolism.
Media headlines claiming that 20 minutes of exercise changes your DNA oversimplify the research and its conclusions. Exercise did not change people’s underlying DNA code or genetics. Instead, exercise was found to reverse a temporary chemical change called methylation, where a particular chemical compound attaches to the outer part of the DNA strand. DNA contains the genetic “code” that the body uses to produce proteins, and methylation alters the rate at which proteins can be produced by the methylated genes.
The effect was only assessed in muscle cells and the participants did not exercise for 20 minutes. Rather, the muscle samples were taken 20 minutes after the participants had stopped exercising.
What kind of research was this?
This human and animal study involved a small number of participants. The researchers reported that previous studies have shown that exercise increases the production of proteins involved in energy usage and other cell functions, but that the mechanism behind these increases was unclear. The researchers thought that a chemical process called DNA methylation may account for this effect, and conducted various experiments to test their theory.
DNA methylation occurs when a chemical compound (called a methyl group) binds to the DNA. Methylation is involved in controlling gene expression, the process by which information contained in DNA is used to create proteins. Methylation of a gene reduces the amount of protein it produces.
What did the research involve?
The researchers recruited 14 men and women, with an average age of 25 years, to complete a single round of exercise on a stationary bike. The participants fasted the night before the sessions. During the experiment, they exercised until they were too tired to want to continue. The researchers took small tissue samples from the participants’ thigh muscles before the exercise session and again 20 minutes after the session.
A sub-group of eight men completed two additional sessions, one low-intensity session at 40% of their maximum aerobic capacity, and another high-intensity session at 80% capacity. The men fasted the night before the sessions. On the day of the experiments, a small sample of thigh muscle was taken and the men then ate a high-carbohydrate breakfast. Four hours after breakfast, they started the exercise session on a stationary bike. They continued cycling until they had expended a predetermined amount of energy (1,674 kJ, approximately 400 calories). A muscle sample was taken immediately after the session, and again three hours later.
The researchers analysed these muscle samples, and compared DNA methylation before and after exercise, and across different exercise-intensity levels. The researchers also looked at methylation levels 48 hours after a three-week exercise programme.
In a separate experiment, the researchers exposed rat muscles in the laboratory to doses of caffeine, which has previously been shown to have similar effects on gene activation to exercise in mice. They then measured gene activation over time.
What were the basic results?
The researchers found that in human muscle tissue, DNA methylation decreased after the single intense bout of exercise. This decrease in methylation led to an increase in the activity of some genes that play a role in various processes in the cell, including those through which the cells generate energy.
When analysing the sub-group of participants who completed both high- and low-intensity sessions, the researchers found that high-intensity exercise led to a greater decrease in methylation than low-intensity exercise.
Further analysis showed that 48 hours after a three-week exercise programme, DNA methylation had returned to the levels seen before the exercise programme. This suggested that the effect is temporary.
The researchers also found that exposing rat muscle to caffeine similarly led to decreases in DNA methylation and increased activity of some genes.
How did the researchers interpret the results?
The researchers say their results suggest that exercise leads to a decrease in the process of DNA methylation in skeletal muscle, and that this decrease is greatest after high-intensity exercise. They believe this decrease may be an early step in the process by which exercise leads to changes in gene expression.
Previous studies have found that levels of proteins involved in the cell’s energy making processes increase after exercise. This new research appears to have found a process that contributes to the phenomenon. It suggests that exercise can lead to changes in gene expression, the process where the body produces proteins based on the genetic code within our DNA. The researchers say that a process called methylation is at least partially responsible for this, although other mechanisms are probably also involved.
The way many news sources presented the research might suggest that exercise actually rewrites a person’s genetic code. This is not the case, as the study found that exercise leads to a temporary change in the DNA strand (called methylation). This affects the rate at which cells produce certain proteins. The significance of this result is not that the DNA fundamentally changes in some way, but rather that the process of methylation appears to be temporarily affected by exercise.
This result is interesting because scientists have generally thought that once methylation has occurred, the chemical modification stays on the gene, and the gene is in a sense “switched off” or at least slows down its production of protein. The researchers say that the study is important because it shows that exercise can alter this process, effectively switching the gene back on temporarily. Again, the significance of this finding is not a change in the DNA itself, but rather that the way the body reads our genetic code appears to be flexible, responding to exercise.
The researchers say that their study provides evidence on how an environmental influence, such as exercise, can cause the muscle to adapt. However, clarifying the mechanism by which this process works is unlikely to influence the daily activities of most people. It’s worth noting that the 20 minutes of exercise described in the Daily Mail’s article is inaccurate. The participants had their muscle samples taken 20 minutes after a session of highly intense exercise had ended. The study does not specify for how long the participants exercised.
The researchers also looked at the effects of caffeine applied directly to extracted rat muscle tissue in the lab. Importantly, in an accompanying article, the researchers emphasised that drinking coffee is not a replacement for exercise, especially since the amount of caffeine required to see the same effect in humans would be close to a lethal dose.
Regular exercise can help maintain a healthy weight and reduce the risk of developing a variety of diseases, such as cardiovascular disease and diabetes. While this study may offer an explanation of how exercise affects muscle tissue, it does not change the underlying message that exercise is good for you.
The Department of Health recommends that adults should get at least 150 minutes of moderately intense aerobic exercise a week, or at least 75 minutes of high-intensity aerobic exercise. Find out more about the UK physical activity guidelines.
Analysis by Bazian