Unlock the Secret Power of Irisin: How Exercise Boosts Your Metabolism and Extends Life!

Introduction

In the quest for optimal health and well-being, scientists have increasingly focused on the intricate relationship between exercise and its profound effects on the body. Among the key players in this dynamic interplay is irisin, a myokine (a hormone produced and secreted by muscle tissue) that has garnered significant attention for its potential to mediate many of the beneficial effects of exercise. Often dubbed the "divinity hormone," irisin has been shown to influence various physiological processes, including fat metabolism, glucose regulation, and even cognitive function and aging. This article delves into the science behind irisin, exploring how different types of exercise impact its levels in the body and how this hormone contributes to overall health and longevity.

What is Irisin? Unveiling the Messenger Hormone

Irisin is a polypeptide hormone secreted by skeletal muscle cells and derived from the fibronectin type III domain-containing 5 (FNDC5) gene. Its production is triggered by the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and released during exercise. This hormone acts as a messenger, traveling through the circulatory system to various organs and tissues, where it exerts its diverse effects.

Early studies in murine models revealed that irisin is associated with higher energy expenditure due to its ability to stimulate the browning of white adipose tissue, regulate glucose uptake, increase lipolysis, and decrease lipid accumulation. In diabetic mice, irisin stimulates glucose uptake and down-regulates gluconeogenesis and glycogenolysis. These findings suggest that irisin plays a crucial role in glucose homeostasis.

The Impact of Exercise on Irisin Levels: A Comprehensive Review

The effect of physical training on circulating irisin concentration has been a subject of much research, with some studies yielding contradictory results. These discrepancies may be attributed to factors such as the variable metabolic condition of the subjects, the method used to assess irisin concentration, and the type of training.

To gain a clearer understanding of the relationship between exercise and irisin levels, a review of existing literature was conducted, encompassing studies published between January 2010 and January 2021. The review included 37 original articles that met specific inclusion criteria, such as longitudinal design, publication in English after 2010, and target populations of healthy participants or those diagnosed with overweight/obesity, type 2 diabetes mellitus (T2D), or metabolic syndrome (MetSx).

The search terms used in the electronic databases (PubMed and Web of Science) included the hormone's name ("irisin") and various types of training interventions ("aerobic", "endurance", "resistance", "concurrent", "combined", "HIIT", "High Intensity Interval Training", "SIT", "Sprint Interval Training", "program", "exercise", and "training").

Aerobic Training and Irisin

Eight interventions consisting of aerobic training by a healthy population were analyzed, and increased irisin concentration was observed in three of these studies. These studies included sedentary and moderately active males and/or females, ages between 59 and 75 years old. Increased irisin levels were also observed in the population displaying different metabolic conditions in three of the seven interventions evaluated. These interventions contemplated sedentary males and/or females with ages between 24 and 61 years old, that exhibited overweight, obesity, or those with MetSx.

The circulating irisin levels did not change in the rest of these studies, either in the healthy population or in the population displaying overweight, obesity, MetSx, or T2D. Therefore, it may be stated that aerobic training promoted increased irisin circulating levels in a population of healthy adults and older adults, with an intensity of 50-75 % of the HRmax, and a 3-5 times/week frequency. Such an increase was observed when the blood sample was obtained between weeks 6 and 10 of the training. When the overweighted/obese population (either with or without MetSx) was considered, a greater training intensity (55-82 % of the HRmax) was required to attain an increase.

Resistance Training and Irisin

Two of the 10 analyzed articles reported an increased irisin concentration. The subjects in these interventions were healthy men or women, older than 62 years old. All subjects trained the main body muscles for 12 weeks with a light intensity, 2 times/week. In the population displaying different metabolic conditions, only one of five articles reported an increased circulating irisin levels. Overweighted or obese 25.8-year-old male and female subjects entered the study and they trained the body main muscles for 8 weeks with an intensity between 65 and 80 % 1RM, 5 days/week.

Conversely, three interventions were analyzed where circulating irisin levels significantly decreased. Sedentary women of ages between 21 and > 60 years old were included in these trials. The subjects trained the main body muscles during 8-16 weeks with a 40-90 % intensity 1RM, 2-3 times/week. Circulating irisin concentration decreased within a 5.4-34.3 % range. However, the results were a function of the metabolic condition, the intensity, and periodization.

It is important to highlight that the main difference between the above three studies and those that report increased irisin levels in healthy populations is the intensity of training. The rest of the studies observed no significant changes regarding circulating irisin levels in healthy subjects or in those displaying overweight, obesity, or MetSx. Therefore, healthy adults with older ages that trained with a light intensity 2 times/week, the increased irisin concentrations appeared within 12 weeks of a resistance training.

Combined Training and Irisin

Five interventions where a healthy population was submitted to combined training were analyzed. Two of such studies showed increased irisin concentrations. Increased irisin concentrations were also observed in three of eight interventions that considered a population displaying different metabolic conditions. Such studies included male and/or female subjects with ages between 7 and 61 years, affected by obesity or T2D, or showing overweight/obesity and MetSx.

Conversely, irisin levels decreased in one intervention that contemplated a healthy population. Irisin concentration decreased by 12.7 % in women with ages 26.60 ± 4.00 years, and untrained, after they performed 8 weeks of aerobic training combined with resistance training, with a 55-75 % intensity of the HRmax and 55-75 % 1RM, respectively, 3 times/week. Of note, HIIT has an important role to increase irisin concentration in a healthy population. However, the greatest increase was observed when HIIT and resistance training were combined. This was also observed for the T2D population.

Circuit Training and Irisin

Three interventions were analyzed where circuit training was performed. Increased irisin levels were detected in these studies. An increase within the 4.1-34.0 % range was observed for female subjects with ages between 26 and 60 years. They were not active or sedentary postmenopausal. After performing a training for 5-8 weeks: either 1 or 3 circuits that combined aerobic and muscle-strengthening training with an 80-90 % intensity of the HRmax or resistance training only with a 55 % intensity of 1 RM, 3 times/week. The irisin increase depended on the assessed VO2max (Maximal Oxygen Uptake) values or if they were older than 30 years. It is noteworthy that only 5 weeks were sufficient to detect increased irisin levels. However, more studies are required where this type of training is executed. An example of a circuit used in one study consisted of 3 circuits consisting of jumping jacks, push-ups, sit-ups, side plank, squats, plank, running in place, lunges and push-ups.

Interval Training and Irisin

Four interventions were analyzed where an interval training was performed by a healthy population. An increase of irisin concentration was detected in two of these studies. Male or female subjects with ages between 23 and 38 years, characterized by performing low physical activity, were included in this study. Increased irisin levels were also observed in a population with T2D.

On the other hand, irisin levels decreased in a healthy population as reported in three of the analyzed interventions. Irisin decreased within a 19.2-38.6 % range in physically active male subjects, ages between 13 and 25 years, after they performed a training on a cycle ergometer or if they practiced basketball for 3-8 weeks with a maximum effort. Regarding interval training it is important to note that changes in circulating irisin concentrations were reported right from week 3. Although some authors indicate that higher irisin levels depend on sex, one study reported that an interval training program induced higher irisin levels in young females whereas it triggered a decreased in males. This agrees with other studies that showed that irisin levels depend on sex.

Factors Influencing Irisin Levels: Intensity, Duration, and Individual Characteristics

Several factors can influence irisin levels in response to exercise. These include:

Intensity: Moderate to high-intensity training, including brief, highly intense intervals, appears to be more effective at increasing irisin levels than low-intensity exercise.
Duration: The duration of exercise may be important to observe increased irisin levels, with some studies suggesting that longer periods of training are needed to elicit a significant response.
Metabolic Condition: Individuals with overweight, obesity, MetSx, or T2D may require a greater training intensity to achieve an increase in irisin levels compared to healthy individuals.
Age: Some studies indicate that irisin secretion is independent of age, while others suggest that older adults may respond differently to exercise in terms of irisin production.
Sex: Some studies have shown that irisin levels depend on sex, with interval training programs inducing higher irisin levels in young females while triggering a decrease in males.
Training Status: Low ATP levels and/or increased phosphate (Pi) or adenosine diphosphate levels promote irisin release, thus ATP homeostasis is restored in working muscle. Consequently, as physical conditioning improves, ATP levels remains steady and circulating irisin does not increase. This suggests that the lower irisin level observed in active subjects is the consequence of an adaptive response towards a greater muscle capacity.

The Multifaceted Benefits of Irisin: Beyond Fat Burning

While irisin's role in converting white fat to brown fat and improving glucose tolerance has been well-documented, its benefits extend far beyond these metabolic effects. Recent research has shed light on irisin's potential to enhance cognitive function and protect against neurodegeneration, as well as its ability to slow down the aging process.

Irisin and Cognitive Function

In October 2013, Spiegelman and his team identified that when irisin is released during endurance exercise, it improves cognitive function and protects the brain against degeneration. They found that raising levels of irisin increased the expression of brain-derived neurotrophic factor (BDNF) and activated genes involved in learning and memory.

Irisin and Aging

On February 17, 2014, scientists from Aston University in the UK published a study showing that irisin slowed the aging process by lengthening telomeres, the protective caps on the ends of chromosomes that affect how quickly cells age. The research team found a significant link between irisin levels in the blood and a biological marker of aging linked to telomere length.

Harnessing the Power of Irisin: Practical Strategies for Everyday Life

While the prospect of an "exercise in a pill" may seem appealing, the reality is that regular physical activity remains the most effective way to boost irisin levels and reap its numerous health benefits. Here are some practical strategies to incorporate into your daily life:

Embrace High-Intensity Interval Training (HIIT): HIIT has been shown to be particularly effective at increasing irisin levels. Incorporate short bursts of intense exercise followed by brief recovery periods into your workouts.
Combine Aerobic and Resistance Training: Combined training approaches have also demonstrated positive effects on irisin levels.
Aim for Moderate to High Intensity: Whether you choose aerobic, resistance, or combined training, aim for a moderate to high intensity to maximize irisin production.
Be Consistent: Regular exercise is key to maintaining elevated irisin levels and experiencing its long-term health benefits. Aim for at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity aerobic activity per week, along with muscle-strengthening activities on two or more days per week.
Consider Circuit Training: Circuit training, which combines aerobic and muscle-strengthening exercises, has also been shown to increase irisin levels.

The 7-Minute Workout: A Quick and Effective Option

For those with limited time, the 7-Minute Workout offers a convenient and effective way to stimulate irisin production. This high-intensity circuit routine consists of 12 exercises performed for 30 seconds each, with 10-second rest periods in between. The exercises target all the body's major muscle groups and provide a full-body workout in a fraction of the time.

Cautions and Considerations

While irisin holds immense promise for improving metabolic health and longevity, it's important to approach exercise with caution and consider individual limitations.

Consult with a Healthcare Professional: Before starting any new exercise program, especially if you have underlying health conditions, consult with your doctor or a qualified healthcare professional.
Start Slowly and Gradually Increase Intensity: If you're new to exercise, start with low-intensity activities and gradually increase the intensity and duration as your fitness level improves.
Listen to Your Body: Pay attention to your body's signals and rest when needed. Don't push yourself too hard, especially when starting a new exercise program.
Proper Form and Technique: Ensure you know how to perform each exercise with proper form and technique to avoid injuries.

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