Type 2 diabetes mellitus (DM), a chronic metabolic disease prevalent in adults, is also prevalent amongst children, adolescents and young adults. On understanding the molecular basis of diabetes, a significant association is found between telomere length (TL) and type 2 DM.
The aim of the study was to review the available evidence on effect of physical activity and yoga on DM including their effect on TL.
The study was conducted in Bangalore.
A number of databases such as Google Scholar, PubMed and Cochrane Review were searched for relevant articles using keywords such as ’diabetes’, ‘type 2 DM’, ‘physical activity’, ‘yoga’, ‘TL’ and ‘telomerase activity’. All types of articles were included for the study, such as randomised controlled trial, systematic reviews, literature review and pilot study. Non-English articles were excluded from the study.
Studies have demonstrated the effectiveness of yoga and physical exercise in type 2 DM in various ways, such as reducing fasting blood glucose and glycosylated haemoglobin; improving lipid profile, blood pressure and waist-to-hip ratio; reducing inflammatory, oxidative and psychological stress markers; and improving the quality of life of patients. However, limited information is available on the effect of these interventions on TL in type 2 DM and mechanisms involved.
Recent studies have shown positive effects of yoga and physical activity on TL. However, there is a dearth of good-quality studies evaluating the effects of yoga on TL in type 2 DM. Future studies need to be conducted with standard treatment protocols, long-term follow-up, appropriate control groups and large sample size.
Diabetes mellitus (DM) is a chronic disease characterised by higher blood glucose levels because of insufficient production of insulin hormone or ineffective use of insulin.
Diabetes mellitus is classified into three main categories namely: type 1, type 2 and gestational diabetes. Out of the three, type 2 DM is the commonest type that accounts for approximately 90% of all the cases of diabetes in adults.
On understanding the molecular basis of diabetes, a significant association is found between telomere length (TL) and type 2 DM.
An important part of management in DM not only includes the treatment of high glucose but also the management of hyperlipidaemia, hypertension, body weight by maintaining a healthy lifestyle that includes a healthy nutritious diet, increased physical activity and cessation of smoking with appropriate use of medications.
The purpose of this study was to review analytically the data available on the effectiveness of yoga and other physical activities in type 2 DM patients. It also aimed to understand and outline the underlying mechanisms responsible for improvement in these patients. The review also attempted to evaluate the effect of yoga on TL from the available evidence and ascertain its implication in type 2 DM.
The articles included for the study were searched from various databases such as Google Scholar, PubMed and Cochrane. The keywords used for the search were diabetes, type 2 DM, physical activity, yoga, TL, telomerase activity and so on. All types of articles were included for the study such as randomised controlled trial, systematic reviews, literature review and pilot study. The articles in language other than English were excluded. The limitation of the method used was that quality analysis and risk of bias assessment was not carried out.
Following were the findings of the review:
Physical activity is one of the important components in the management of diabetes. Physical inactivity is one of the important modifiable risk factors for type 2 DM.
In a systematic review and meta-analysis on diabetic patients over 18 years of age, regular physical activity in the form of aerobic and resistance exercises (for 8 weeks or more) were effective in reducing blood sugar level in the short term, and in the long term, the levels of HbA1c were significantly reduced (0.60% lower than the control group).
In another study on pre-diabetic individuals (intermediate hyperglycaemia according to World Health Organization [WHO]), the effect of structured exercises (according to ADA guidelines) on sedentary obese individuals (less than twice per week of aerobic exercise) was evaluated.
A pilot study showed that 6 weeks of functional high-intensity crossfit training (three sessions of resistance training, gymnastics and aerobic exercises for 10–20 min) improved function of beta cells by reducing fasting pro-insulin or insulin ratio (responsible for the processing inefficiency of insulin), decreased abdominal fat and improved liver function. Abdominal fat is connected to insulin resistance which, in turn, relates to beta cell dysfunction. This study can be an effective approach to improve the adherence to the treatment plan in type 2 DM patients because of structured programme for a short time period. Nevertheless, given the differential response to exercise, further studies need to perform to devise the most effective exercise regimen.
In a systematic review by Hemmingsen et al., the effect of diet or physical activity alone or effects of both were evaluated. It was concluded that there was no effect of diet or physical activity alone on the risk of type 2 DM on people at high risk of developing type 2 DM. Nonetheless, diet plus physical activity together reduced or delayed the incidence of type 2 DM in people with IGT. However, the effects on complications of DM and prediabetes were not investigated.
Another study examined the effect of lifestyle interventions on the risk factors for cardiovascular disease in type 2 DM. These interventions included changes in diet, exercise and education (at least one of smoking cessation, behaviour modification, counselling and so on) for more than 6 months duration. Results showed significant improvements in BMI, HbA1c, systolic and diastolic BP (all
Apart from the structured physical activity, studies have proven efficacy of daily physical activity too. Daily physical activity includes different activities carried out during both leisure time as well as during work. For example, walking, gardening and household activities that can be easily performed by type 2 DM patients. A review by Hamasaki
A study showed that diabetic patients encounter various facilitators (awareness of benefits of exercise and complications of DM and family support) and barriers (time constraints, lack of perception of obesity as a health issue, inability to associate exercise with blood sugar control, sociocultural issues, improperly trained diabetic educators) to an exercise programme. These should be taken into account to improve the knowledge and adherence to the exercise programme.
In summary, it can be concluded that physical exercise has a significant role in improving glycaemic control and reducing the risk of cardiovascular disease in patients with type 2 DM. However, there was a problem in patient adherence to the treatment programme. Lower physical performance, low-energy expenditure, cardiorespiratory fitness and muscle strength inversely associate with the degree of diabetic complications.
Following are the updated guidelines on exercise in diabetes:
Aerobic exercise: 150 min or more of moderate to vigorous activity per week for at least three or more days a week.
High-intensity interval training: Short bursts of high-intensity exercise with retrieval period either in the form of rest or an activity of low-intensity results in better insulin sensitivity and better overall blood glucose levels.
Resistance exercises: Variety of strength training on non-consecutive days for two to three sessions per week. Heavy training has a better impact on glycaemic control, strength, balance and ability to live life self-sufficiently than lighter exercises or home-based activities. Resistance training followed by aerobic exercise helps to maintain the glycaemic balance.
Flexibility and balance exercises: Performed two to three times per week. Stretching exercises help to improve the range of motion and gait and balance training prevents falls in elderly. Yoga improves glycaemic control, lipid levels and body composition in adults. Tai chi training helps to improve glycaemic control, stabilises symptoms of neuropathy and improves the QOL of the patients.
Daily unstructured physical activity: Such as household tasks, gardening, dog walking, and so on, helps in losing and maintaining weight, reducing post-prandial blood sugar.
Aerobic exercises are better over resistance training in terms of improvement in glycaemic control. Both have similar effect over the cardiovascular risk markers. The combined effect of both the exercises leads to better management of blood glucose.
Aerobic as well as resistance exercises have shown to increase muscle GLUT4. This increase in GLUT4 probably leads to the increased capacity for insulin-stimulated glucose transport in trained subjects.
The term ‘Yoga’ is derived from the Sanskrit word
A systematic review of controlled trials performed on the effect of yoga on type 2 DM revealed that yoga produced significant effect on various parameters in DM treatment and prevention. These factors include glycaemic control (FBG, postprandial blood glucose [PPBG], fasting insulin and HbA1c), insulin resistance, reduction in low-density lipoprotein (LDL) and increase in high-density lipoprotein (HDL), reduction in waist-to-hip ratio and reduction in BP.
Another systematic review and meta-analysis concluded similar results on the beneficial effects of yoga on FBG, PPBG and HbA1c levels.
In another meta-analysis, similar results were obtained. Yoga significantly reduced levels of FBG, PPBG, HbA1c, total cholesterol (TC), LDL and increased the levels of HDL. Henceforth, the study suggested that yoga can be considered as a possible alternative management for type 2 DM. However, the studies varied much in terms of participant characteristics, parameters and the forms of yoga. Hence, further studies are required to determine the appropriate exercise programme and long-term effects of yoga with the help of objective measurements such as QOL, BP, inflammatory mediators and immune cell function.
A recent review also showed the beneficial effects of yoga on blood glucose levels (FBG, PPBG, usage of anti-diabetic drugs and management of comorbid diseases in type 2 DM patients). The study stated that yoga helps in prevention and control of DM, control of body weight, BP and lipid profile, prevention of cardiovascular events, complications of DM, pancreatic regeneration and exercise tolerance. It also helped to improve the QOL, mood and stress levels, coagulation profile and cognitive function of patients. However, the study lacked proper control groups, appropriate sample size, appropriate duration, proper methodology, and so on. Hence, further studies need to improve methodology, reduce bias and study long-term effects of yoga.
In another systematic review and meta-analysis, the studies included had a control group, reported an objective measure of glycaemic control and had follow-up of at least 8 weeks. The study showed that yoga had significant improvement in glycaemic outcomes (HbA1c, FBG and PPBG), lipid profiles, BP, BMI, waist-to-hip ratio and cortisol levels.
A randomised controlled trial on 80 subjects (35–55 years old) evaluating the effect of yogasanas and pranayama in type 2 DM patients (with disease duration ranging from 1 to 10 years) found that there were significant reductions in the levels of FBG, PPBG and HbA1c (
In another randomised trial,
In conclusion, yoga is an effective alternative or complementary treatment in type 2 DM. However, future studies should focus on conducting high-quality studies with proper control groups, appropriate methodology of yoga interventions, appropriate (large) sample size, patient adherence to the treatment, long-term follow-up and outcome measures other than blood glucose parameters.
The following are the possible mechanisms responsible for the beneficial effect of yoga in type 2 DM.
Firstly, yoga may help to reduce the negative effect of stress and contribute to various positive effects on metabolic, neuroendocrine function and the associated inflammatory reactions. Thus, it helps to lower the risk for cardiovascular diseases by improving the well-being and decreasing the activation of hypothalamic–pituitary–adrenal (HPA) axis and sympathoadrenal system.
Secondly, yogic training may cause a shift from sympathetic to parasympathetic stimulation by directly increasing the parasympathetic output probably via vagal stimulation. This results in positive effects on neuroendocrine, haemodynamic and inflammatory markers, sleep and other metabolic parameters.
Thirdly, yoga may also aid in causing desirable changes in autonomic balance, memory, mood, neurological function and other related metabolic and inflammatory responses by activating specific brain structures and neurochemical systems related to attention and positive affect.
In addition, yoga also helps those with type 2 DM indirectly by improving attitudes related to health and lifestyle, providing a source of social support. Yoga is also found to improve flexibility, muscle strength, blood supply and oxygen uptake.
The stretching of abdomen during yogic exercise is thought to regenerate β pancreatic cells, improving their sensitivity to glucose and improving secretion of insulin.
Yoga also leads to changes in level of hormones and neurotransmitters such as β endorphin, serotonin, dopamine, arginine vasopressin, melatonin, and so on. These changes result in joy, euphoria, improvement in arousal, calming effect and blissful feelings, respectively.
Yoga is thought to have the potential to bring stem cell trafficking from bone marrow to the peripheral blood, which, in turn, may contribute to tissue regeneration. Nevertheless, this area needs to be explored further.
Yoga reduces oxidative stress by lowering the levels of malondialdehyde (MDA), interleukin 6 and leptin and improving the levels of adiponectin.
In an exploratory study, it was concluded that yoga is more advantageous than individual treatments such as physical exercise, caloric restriction and antioxidants.
The ‘telomere’ concept was given by McClintock and Muller.
Telomere length can be measured by various methods.
Telomerase is a ribonucleic acid (RNA) containing enzyme which helps in synthesis of telomeric DNA on the ends of chromosomes. Thus, it maintains the integrity of genomes in the embryonic stem cells. Over the long term, it aids in improving the telomere maintenance.
Various studies have evaluated the effects of physical activity and yoga on TL and telomerase activity in various conditions.
A review on the effect of asana, pranayama and meditation on TL and telomerase activity demonstrated that asana and pranayama improve the flow of oxygen to the cells. Meditation was found to decrease the stress levels by changing the HPA axis. Hence, it can play an important role in contributing to human health and lifestyle disorders. In the review, it was found that most studies used quantitative polymerase chain reaction to quantify the TL in peripheral blood mononuclear cells (PBMCs). Following were the findings of the review.
A pilot study was performed on patients with prostate cancer to evaluate the relation between lifestyle modifications (yoga-based stretching, breathing and meditation) and TL. The study revealed that after 5 years of lifestyle modification, there was 10% increase in TL, whereas the control group had 3% reduced TL (
A prospective case control study by Krishna et al. evaluated the effect of yoga on leucocyte telomere biology and its relation with homocysteine, MDA and oxidative stress in healthy individuals.
A study by Tolahunase
Thus, the above review indicated that yoga has a positive effect on TL. Nonetheless, there are only a few trials with very small sample sizes. Hence, there is a need for randomised trials including healthy control group and in specific diseases.
A systematic review by Deng et al. found that the practice of physical exercise, diet, yoga and mindfulness meditation increased the telomerase activity. However, the exact mechanisms for the changes in telomerase activity have not been elucidated. Future research should include studies depicting relation between chronic psychological stress, depression, mediation and physical exercise to telomerase activation.
Various studies evaluated the effect of physical exercise on TL and DNA damage.
Studies have shown that yoga affects TL and telomerase activity through various mechanisms as follows:
Yogic activities that make use of diaphragmatic breathing have shown to either decrease the production of ROS or enhance the stimulation of enzymes responsible for rapid destruction of ROS or both. In one study involving yeast, it was found that elevated oxygen consumption reduced the generation and release of ROS.
Yoga is also found to increase the levels of the enzyme superoxide dismutase (SOD), which converts the superoxide anion O2− (the major ROS produced in cells) into hydrogen peroxide. This, in turn, is then removed by glutathione (GSH) peroxidase or catalase, thus inhibiting the collection of ROS. This result was found in a study performed by Bhattacharya et al. on the effect of yogic breathing exercise on ROS levels.
Another study demonstrated that yoga helps to reduce the MDA levels (one of the primary products of lipid peroxidation by ROS) following vipassana practice, thus concluding that TL is inversely related to MDA levels in yoga group.
Yogasanas also involve slow, smooth stretching of the muscles without any resistance. This sustained passive stretch improves the circulation around the tissues and organs, and thus helps in removing metabolic waste products like oxidative stress and reduces molecular damage to the cells.
A study has also shown that yoga causes an increase in the levels of β endorphin and sirtuin-1 and decrease in the levels of cortisol and interleukin-6 by producing changes in the brain through HPA axis.
The current review demonstrates the beneficial effects of yoga and physical exercise such as aerobic and resistance exercise in the management of type 2 DM. Physical exercise is thought to improve muscle mass, glucose transport and insulin secretion. The beneficial effects of yoga include stress reduction, positive effects on metabolic and neuroendocrine function and inflammatory reactions. These effects are probably because of decrease in the activation of HPA axis, shift from sympathetic to parasympathetic stimulation, change in autonomic balance, mood, memory, regeneration of pancreatic cells, muscular relaxation, change in the level of hormones and neurotransmitters such as beta endorphin, serotonin, dopamine, and so on, and reduction in oxidative stress by lowering the levels of IL-6, MDA and leptin. On comparing the effects of yoga and exercise, contrasting evidences were seen. Few studies showed the superiority of yoga over physical exercise, whereas few studies demonstrated equal effectiveness of the two treatments. Yoga is found to have positive effects on TL and telomerase activity. The mechanisms include reduction in ROS, MDA and cortisol levels and increase in SOD, TAOS and β endorphin levels in addition to improvement in blood circulation. These mechanisms, in turn, reduce the oxidative stress reversing the cellular ageing and improving cell longevity. However, most of the studies were conducted on healthy adults without control group and with small sample size. Thus, there is a need to conduct good-quality randomised controlled trials, which focus on evaluation of effects of specific standardised yoga intervention protocol on TL and telomerase activity in specific conditions like type 2 DM, with large sample size, appropriate control group and long-term follow-up. Given the increasing prevalence of type 2 DM amongst children and adolescents, future studies also need to be conducted in different age groups (including children and adolescents). The review also suggests to conduct good-quality comparative studies to evaluate the effects of yoga over physical exercise on TL in type 2 DM in future.
The authors have declared that no competing interests exist.
R.A.U. (Manipal Academy of Higher Education) has made substantial contribution to conception, design and acquisition of data. She has given final approval of the version to be published. R.A.U. (Saurashtra University) has been involved in conception, design, acquisition of data, drafting of the manuscript and revising it.
This article followed all ethical standards for research without direct contact with human or animal subjects.
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Data sharing is not applicable to this article as no new data were created or analysed in this study.
The authors admit that the article submitted is their own.