INTRODUCTION

Diabetes mellitus is defined as a set of metabolic changes characterized by chronic hyperglycemia, which occur due to the destruction of beta cells in the pancreas, resistance to the action and/or insulin secretion disorders¹.

Diabetes mellitus can be classified into the following categories: type 1 diabetes, type 2 diabetes, gestational diabetes mellitus and diabetes originating from other specific causes^2-3. However, the study will focus on type 1 and type 2 diabetes mellitus.

Type 1 diabetes mellitus arises when beta cells are destroyed, leading to deficient production of insulin in the body. The cause for this type of diabetes is not known yet. The symptoms include: excessive thirst, frequent urination, hunger, weight loss, changes in vision and fatigue^2-3.

Type 2 diabetes mellitus occurs due to an alteration in insulin secretion leading to body insulin resistance. This type of diabetes is one of the most frequent and the symptoms are very similar to type I diabetes mellitus, but generally less evident or even absent^2-3.

Diabetes mellitus has become one of the most important public health challenges of the 21^st century. Until the last decade, it was underestimated, and currently it is seen as a threat to global public health ⁴.

In 2014, worldwide, it was estimated that 422 million adults had diabetes, an increase compared to 1980, which had a prevalence of 108 million people. The overall (age-standardized) prevalence of diabetes has nearly doubled since 1980, rising from 4.7% to 8.5% in adults. This increase is associated with risk factors such as overweight or obesity³.

In Portugal, there is a statistically significant difference in the prevalence of Diabetes between men (15.9%) and women (10.9%), as well as the existence of a strong increase in the prevalence of diabetes with age (more than one quarter of people aged 60-79 years have diabetes) ⁵.

Among the various types of diabetes, type 2 diabetes mellitus is the most common, representing about 90-95% of cases⁶. Some risk factors for this type of diabetes are: genetics, ethnicity, age (non-modifiable factors), overweight or obesity, unhealthy diet, insufficient physical activity and smoking (factors modifiable through behavioral and environmental changes) ³.

Regular physical activity is important for everyone, but it is especially relevant for people with diabetes, being considered as an adjuvant in prevention and treatment⁷.

Physical activity includes all movements that result in energy expenditure above the resting level. Physical exercise, on the other hand, is a type of activity that consists of programmed, structured and systematically repetitive body movements that aim to improve physical preparation⁶.

Physical exercise, in addition to healthy eating habits, is one of the first strategies recommended for people newly diagnosed with type 2 diabetes mellitus, bringing benefits in terms of reducing the risk of diabetes and increasing blood glucose³ being essential for cardiovascular risk reduction, weight loss or control and general well-being. Physical exercise, whether aerobic, resistance or a combination, facilitates glucose regulation. High-intensity interval exercise is effective and has the advantage of being very efficient in terms of time⁷.

Regular physical exercise also brings considerable benefits to the health of people with type 1 diabetes mellitus, specifically, at the cardiovascular level, muscle strength and insulin sensitivity⁶.

Aerobic exercise is a type of exercise that involves continuous and rhythmic movements of large muscle groups, such as walking, running and cycling.⁸ This impacts on the increase in mitochondrial density, insulin sensitivity, oxidative enzymes, blood vessel reactivity, pulmonary function, immune function and cardiac output. In type 1 diabetes mellitus, aerobic exercise increases cardiorespiratory fitness, decreases insulin resistance and improves lipid levels and endothelial function⁶, while in people with type 2 diabetes mellitus, it improves blood glucose control, insulin sensitivity , oxidative capacity and important related metabolic parameters⁸.

Resistance exercise is synonymous of strength training and includes movements using free weights, weight machines, body weight exercises or elastic resistance bands⁸. At the level of type 1 diebetes mellitus, resistance exercise in the control of capillary blood glucose is not well defined, however it can help to minimize the risk of hypoglycemia induced by physical exercise⁶. In people with type 2 diabetes mellitus, resistance exercise brings gains, namely in terms of strength, bone mineral density, blood pressure, lipid profile, cardiovascular health, insulin sensitivity and muscle mass⁸.

In relation to mobility and balance exercises, these are more relevant in elderly people with diabetes. The limited joint mobility often observed in this population results in part from the formation of advanced glycosylation end-products, which accumulate during normal aging and are accelerated by hyperglycemia⁶.

Stretching exercises contribute to increased mobility, but do not affect glycemic control, while balance exercises can reduce the risk of falls⁶.

The specialist nurse in rehabilitation nursing has specialized knowledge and skills, intervening in an individual and unique way, taking into account the needs, characteristics, abilities and tolerance of each person⁹.

It is also responsible for monitoring and implementing rehabilitation programs, evaluating and making the necessary adjustments in the care delivery process. In this way, it makes it possible to improve the quality of life, through the improvement of functionality and autonomy, involving physical, social and emotional dimensions⁹. This systematic literature review is intended to identify: "What are the benefits of physical exercise for people with diabetes?". It was chosen because of its current prevalence, which gives it special importance in the area of ​​expertise of the Specialist Nurse in Rehabilitation Nursing.

Thus, this systematic literature review (SLR) aims to assess the effects of physical exercise in people with diabetes.

MATERIAL AND METHODS

Nursing Research is a systematic, scientific and rigorous method that seeks to develop and deepen knowledge in this area, seeking to answer questions or solutions to problems for the benefit of the person, family and community¹⁰.

Scientific investigations in the field of nursing have been increasing, especially clinical research, with well-designed methods and a strong level of evidence, in order to support evidence-based practice (EBP)¹¹.

SLR is a scientific methodology that makes it possible to identify, evaluate and abbreviate studies carried out by researchers, academics and health professionals. The starting point is a well-designed and formulated question using systematic and clear methods, also allowing for the collection and analysis of data from the studies that were included in the review^12-13. For an analysis of all the available evidence, it is essential to follow the following steps: clearly define the objectives considering the eligibility criteria; explicit and reproducible methodology, systematic research that shows that all studies meet the eligibility criteria; evaluation of the authenticity of the results of the included studies^12-13.

The research question of this study was conducted through the PICO method - Participant (Type of Participants); Intervention (Type of Intervention); Comparasion (comparison); Outcomes (Type of Results), as shown in table 1.

Having said that, the following research question was defined for this Systematic Literature Review: “What are the benefits of Physical Exercise for People with Diabetes?”.

The research for the systematic review of the literature was defined as a function of the research question, the descriptors related to each of the components of the PICO strategy and keywords as shown in table 2. The descriptors were previously validated in the platform Descriptors in Health Sciences and Medical Subject Headings.

The investigation took place in November 2018 through two independent surveys. Based on the aforementioned descriptors, the research was carried out in electronic database platforms: EBESCO host, Medline and Virtual Health Library.

Given the specificity of the topic and the large number of studies/articles found, it was necessary to define inclusion and exclusion criteria (Table 3) in order to help in the selection of studies/articles relevant to the development of the topic in question.

From the bibliographic research process carried out with this methodology, we obtained 1039 articles for the initial selection. Out of these, 910 were rejected by title or subject and 30 by abstract. Out of the resulting 18, 7 were excluded after analysis of the full text, as they did not meet the defined inclusion criteria, with the final result of 10 articles included that met the inclusion criteria.

Table 4 describes the process of combining descriptors and keywords for searching the databases. Figure 1 illustrates the PRISMA¹⁴ flowchart corresponding to the identification, analysis, selection and inclusion of articles.

Figure 1 Identification, analysis and selection of articles.¹⁴  

The articles selected for full reading were independently evaluated by two investigators, taking into consideration the methodological quality criteria proposed by the Joanna Brigggs Institute (JBI), Assessment and Review of Information¹⁵ and articles which met more than 75% of the criteria were selected.

The information was extracted from the articles on authors, year, country, sample, data on physical exercise (modality, frequency, intensity, volume and duration), conclusions and level of evidence. The levels of evidence of the included studies were classified according to the criteria of the Registered Nurses Association of Ontario, as shown below: Ib-Evidence determined from at least one randomized controlled study^16-17.

RESULTS

In this SLR, 9 articles were published in the following years: 2014^20-21,23, 2015¹⁹, 2016²⁴ and 2017^18,22,25-26. The sample of people with diabetes who underwent the intervention ranged between 12¹⁸ and 536²⁶. The control group ranged between 5¹⁸ and 149²⁶. All studies included (Table 5) are experimental studies, with level of evidence Ib, that is, evidence obtained from a well-designed study and through at least one randomized controlled study¹⁵, which is therefore an added value for this SLR.

DISCUSSION

The modalities of physical exercise most applied in the selected studies were: walking^{18,20-21,23-24}, resistance machines, free weight^22,25 and bicycle²⁴. The type of physical exercise recommended for the diabetic person will depend on some factors, namely their baseline physical condition, preferences, available means or the presence of physical limitations¹⁹.

The analyzed studies resorted essentially to aerobic exercises, with the exception of the studies of Karimi et al.,²² and Otten et al.,²⁵ that combined aerobic and resistance exercises. Some studies reported that the combination of aerobic physical exercise in addition to resistance training may be better than any of them separately²⁰.

The frequency of exercise evidenced in the studies ranged between twice a week¹⁹ and 5 to 6 times a week²⁰ and lasted between 30 minutes²² and 60 minutes^24-25 for each session of exercise. The minimum frequency of exercise recommended by the American Diabetes Association is 150 minutes per week of moderate aerobic exercise over at least three days a week; the Spanish Diabetes Society, on the other hand, recommends exercise sessions lasting at least 45 minutes, three times a week, divided into pre-warming, the main phase and finally relaxation²⁰.

Exercise intensity was not evaluated equally in the articles analyzed and not all made reference to this parameter. Asuako et al.,¹⁸ assessed intensity using the maximum heart rate, a value obtained using a pulse oximeter version 803, China, placed during exercise and using the online Pace Calculator application.

In the studies carried out by Dixit et al.,²⁰ and Taylor et al.,²¹, the exercise intensity was evaluated using the Karvonen formula (Training heart rate = Rest heart rate + (Intensity) x (Maximum heart rate - Heart rate) at rest). Dixit et al.,²⁰ used a heart rate monitor (Polar Electro Oy, Kempele, Finland) and used it to monitor heart rate continuously during aerobic exercise.

It should be noted that in the analyzed studies, the characterization of the exercise was not always complete (modality, type of exercise, frequency, intensity, volume and duration) which limited the analysis, somehow limiting the generalization of the results.

In the analysis performed, only two articles combined the study of exercise with a specific type of diet^25-26.

Otten et al.,²⁵ combined physical exercise with a paleolithic diet, a diet based on the consumption of lean meat, fish, seafood, eggs, vegetables, fruits, berries and nuts and excluding cereals, dairy products, vegetables, refined fats, refined sugars and salt. In previous studies, the paleolithic diet had beneficial metabolic effects on obesity and the type of diabetes²⁵.

Vlaar et al.,²⁶ combined physical exercise with a healthy diet based on the national food guidelines for South Asia and which includes 2 pieces of fruit/day, vegetables (200g/day), whole wheat (whole wheat products exclusively), rice (only brown rice) and 3 meals a day/regular time.

By analyzing the articles, we found that there are important health gains for people with diabetes associated with the practice of physical exercise. The most used variables in most studies and which show these gains were glucose²⁰, HbA1c^19-25, body weight^18-25 and cholesterol^18-19, associated with more controlled glycated hemoglobin values ​​and lower cardiovascular risk, also improving the psychosocial health status and decreasing pharmaceutical costs ¹⁹.

CONCLUSION

With this SLR and after analyzing the 9 studies, we can conclude that exercise brings benefits to people with diabetes, namely in terms of reducing fasting plasma glucose, glucose hemoglobin values, reducing body weight and cholesterol, as well as improving the person's quality of life.

This study allowed increasing knowledge in rehabilitation nursing, as well as contributing to the assessment of the benefits of structured physical exercise in people with diabetes. However, there were gaps in the description of exercises in terms of modality, frequency, intensity, volume, duration and progression. Further studies are recommended, with a more robust sample, where interventions within the scope of physical exercise are more objectively described, as well as the assessment instruments that allow not only to define exercise intensity, but also to demonstrate prescription-sensitive gains exercise performed by specialist nurses in rehabilitation nursing.