Can Exercise Make You Younger? The Science of “Rejuvenation Hormones,” Muscle, and Aging

Can Exercise Really Make You Younger? What Current Research Tells Us

You often see the phrase “exercise makes you younger.” So, how much do we know from research?

First, studies that have followed large numbers of people over many years have repeatedly reported that those who exercise regularly tend to have a lower risk of death and disease.

However, this does not mean that exercise has been proven to return the body to a younger state. Recently, reports have also emerged showing that exercise can change “markers of cellular aging” in the blood. However, most of these studies still involve small numbers of participants.

This article will explore ①what has been learned from long-term studies, ②substances produced by exercise, and ③research on markers of cellular aging, in that order.

How Many Minutes of Strength Training Per Week Are Best? Is More Always Better?

There is research summarizing the relationship between strength training and longevity. In 2022, a research group including researchers from Tohoku University analyzed 16 previously published studies involving adults aged 18 and older and reported their findings (this type of analysis is called a “meta-analysis”).

The results showed that people who engaged in strength training had about a 10–17% lower risk of death from all causes, heart disease, stroke, cancer, and diabetes compared to those who did not.

Interestingly, the relationship with time was noteworthy.

• The lowest risk of death from all causes was associated with about 40 minutes of strength training per week (about 17% lower).
• For death, heart disease, stroke, and cancer, the risk followed a “J-shaped” curve. The risk decreased most at around 30–60 minutes per week, and the reduction leveled off as exercise time increased further.
• For up to about 130–140 minutes per week, the risk remained lower than for those who did not do strength training. There was insufficient data for more than that, and the results remain unclear.
• For diabetes, the risk decreased significantly up to about 60 minutes per week, after which it leveled off, forming an “L-shaped” curve.

In other words, this research suggests that more strength training is not necessarily better. Researchers also stated that the effects of exercising more than that are unclear.

Additionally, people who did both strength training and aerobic exercise, such as walking, had about a 40% lower risk of death from all causes compared to those who did neither.

However, this study relied on self-reported data about whether participants engaged in strength training and did not establish a causal relationship between strength training and increased longevity. The authors also noted the small number of studies as a limitation.

How Do Daily Steps, Walking Speed, and Sitting Time Affect Longevity?

Even for those who do not do strength training, daily walking appears to play a role.

Daily Steps

One study followed approximately 4,800 Americans aged 40 or older using pedometers (accelerometers) for about 10 years (2020). Compared to those who took 4,000 steps per day, people who took 8,000 steps had about half the risk of death from all causes (0.49 times), while those who took 12,000 steps had about one-third the risk (0.35 times). However, when the effects of step count were accounted for, walking speed (intensity) showed no clear relationship with mortality.

Walking Distance and Dementia

A study of approximately 2,300 men aged 71–93 living in Hawaii found that those who walked less than about 400 meters per day had about a 1.8 times higher risk of developing dementia compared to those who walked 3 kilometers or more (2004).

Walking Speed

A study analyzing data from approximately 34,000 people aged 65 or older found that faster walking speed was associated with higher survival rates (2011).

Sitting Time

A study that followed approximately 17,000 Canadians aged 18–90 for about 12 years found that people who spent most of their day sitting tended to have a higher risk of death. This relationship was observed regardless of whether they exercised in their leisure time (2009).

All of these are “observational studies,” which suggest associations but do not establish cause and effect. For example, people who are naturally healthier may be able to walk more.

What Are the “Rejuvenation Hormones” Produced by Exercise? Why Are They Debated?

Many people search for the term “exercise rejuvenation hormone.” However, this is not an official scientific term. It is primarily used to refer to substances released by muscles during exercise.

Muscles are not just tissues that move the body. They are thought to release hundreds of different proteins and other substances into the bloodstream, sending “signals” to fat, the liver, bones, and the brain. These substances are called “myokines” (myo = muscle, kine = active substance).

One substance that has received particular attention is “irisin.” In 2012, a U.S. research group discovered this substance in mouse muscle and reported that it was produced by exercise and made fat easier to burn for energy. This discovery led to irisin being called an “exercise hormone” and other terms, drawing significant attention.

However, this has since become a subject of debate.

• In 2015, research groups in Germany and elsewhere reported that a commercially available test kit used to measure irisin in human blood had also reacted to proteins other than irisin. They pointed out that previous measurements may therefore have been questionable.
• In the same year, the original research group used a more accurate method (mass spectrometry) to examine human blood and reported that irisin was indeed present. Levels were about 3.6 ng/mL in people without a regular exercise routine and about 4.3 ng/mL in people who trained for endurance, showing only a slight difference.

Although it has now been shown that irisin is present in human blood, its function in the human body is still not fully understood. The effects observed in mice may not apply to humans.

Substances produced by exercise are not limited to those released by muscles. A 2020 mouse study reported that when the blood plasma of older mice that had exercised was injected into older mice that had not exercised, new neurons were more likely to form in the brain, and the mice performed better on memory tests. The enzyme involved was produced in the liver. However, this was an experiment using mice.

In this way, research is gradually revealing that exercise sends “signals” throughout the body. However, it is not yet at a stage where researchers can say, “This substance makes you younger.”

Can Exercise Change “Markers of Cellular Aging”?

When looking at the aging of the body at the cellular level, it is thought that the accumulation of “senescent cells,” which stop dividing but do not die, plays a role. Proteins that stop cell division, such as p16 and p21, are used as markers of senescent cells.

A research group at the Mayo Clinic had 34 older adults with an average age of 67 participate in a 12-week program combining strength training twice a week with endurance exercise (2021). The following changes were reported:

• The activity of genes related to aging, such as p16 and p21, was reduced in immune cells (T cells) in the blood
• Some proteins associated with inflammation and other processes produced by senescent cells were reduced in the blood
• Performance on tests of grip strength, rising from a chair, and walking improved

This study attracted attention as an early report examining the relationship between exercise and markers of cellular aging in humans. However, the number of participants was small, and there was no “control group” of people who did not exercise. The researchers themselves noted the lack of a control group as a limitation. Furthermore, it is not yet known whether the reduction in markers in the blood led to fewer diseases or increased longevity.

Can Yoga and Meditation Change Markers of Cellular Aging?

A research group in India is investigating how markers of cellular aging change with lifestyle programs centered on yoga and meditation.

Report on One 31-Year-Old Man (2015)

This report followed one obese 31-year-old man who participated in a 10-day yoga program (including poses, breathing techniques, stress management, and lectures) and was examined for up to 90 days afterward. Telomerase activity—an enzyme that lengthens “telomeres” at the ends of chromosomes—and β-endorphin levels increased, while markers of oxidative stress and DNA damage decreased. However, because this was the record of only one person, it cannot be concluded that the program is effective.

Study of 96 Healthy People (2017)

The same group conducted a study in which 96 healthy people participated in a 12-week yoga and meditation program. Telomerase activity increased, while cortisol, IL-6, and oxidative stress markers decreased. However, although the length of the telomeres themselves tended to increase, there was no clear difference. This study also had no control group.

Research on the relationship between yoga or meditation and cellular aging is still primarily limited to small studies. Larger studies with control groups are needed to make definitive statements about humans.

What to Know When Starting Exercise

The following is a summary of what can generally be concluded from the research covered so far.

• Even a Little Is Better Than None: Studies on daily steps and strength training showed a large difference in risk between being completely inactive and becoming slightly active.
• Strength Training in Moderation: Strength training appeared to be associated with the lowest risk of death at around 30–60 minutes per week. More is not necessarily better.
• Combine Exercises: People who did both strength training and aerobic exercise tended to have a lower risk.
• Reduce Sitting Time: In addition to the time spent exercising, the amount of time spent sitting was also important.

If you have a medical condition, are older, or have not exercised for some time, please consult your doctor before starting a new exercise routine. If you experience pain or shortness of breath, stop immediately.

What to Keep in Mind When Reading Research

Research on exercise and aging is often featured in the news and on social media. Keeping the following points in mind can help you read the information more carefully.

• Observational Study or Trial: Many studies showing that “people who exercise regularly live longer” are observational studies. It is difficult to distinguish whether exercise is the cause or whether naturally healthier people are more likely to exercise.
• Humans or Mice: Many studies on irisin and blood components involve experiments using mice.
• Number of Participants and Control Group: Studies examining markers of cellular aging often involve dozens to about 100 participants and are frequently conducted without a control group.
• Did Markers Change, or Did Health Improve?: Even if markers in the blood change, this does not prove that the changes reduced disease or increased longevity.

Frequently Asked Questions

Q. Should I do strength training every day?

A. An analysis of 16 studies found that the risk of death was lowest when people did about 40 minutes of strength training per week. The results did not show that more is always better. However, this was an observational study, and the optimal amount has not been established. It is important to continue exercising within a range that is manageable for your fitness level and physical condition.

Q. Does exercise produce a lot of “rejuvenation hormones”?

A. “Rejuvenation hormone” is not an official term; it is primarily used to refer to myokines and other substances released by muscles during exercise. While irisin, a representative substance, has been confirmed to be present in human blood, the increase caused by exercise is slight, and its function in humans is still not fully understood.

Q. How many steps should I take per day?

A. A U.S. study found that people who took 8,000 steps per day had about half the risk of death compared to those who took 4,000 steps. However, this showed that people who took more steps had a lower risk; it is not a target that guarantees better results regardless of the number of steps.

Q. Does yoga stop cellular aging?

A. There have been reports that markers such as telomerase activity changed with yoga and meditation programs. However, these are primarily records of only one person or studies without a control group. It is not yet at a stage where researchers can say that yoga stops cellular aging.

Summary

Related Pages

• Research Column: “What Are Senescent Cells?”
• Research Column: “Is Rejuvenation Possible?”

Citations and References

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3. Abbott RD, et al. Walking and dementia in physically capable elderly men. JAMA. 2004.
4. Studenski S, et al. Gait speed and survival in older adults. JAMA. 2011.
5. Katzmarzyk PT, et al. Sitting time and mortality from all causes, cardiovascular disease, and cancer. Medicine and Science in Sports and Exercise. 2009.
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7. Boström P, et al. A PGC1-α-dependent myokine that drives brown-fat-like development of white fat and thermogenesis. Nature. 2012.
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12. Kumar SB, et al. Telomerase activity and cellular aging might be positively modified by a yoga-based lifestyle intervention. Journal of Alternative and Complementary Medicine. 2015.
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