Relationship between Quality of Life and Cardiorespiratory Endurance in Patients with Type 2 Diabetes

Diabetes is a metabolic disease characterized by chronic hyperglycemia and impaired metabolism of carbohydrates, lipids and proteins. This disease is caused by defects in insulin secretion, insulin function, or both (1, 2). This chronic disease can have serious short-term and long-term consequences that affect the health and quality of life (QOL) of patients (3). Type 2 diabetes accounts for approximately 90% of all cases of diabetes and is associated with a variety of immutable and modifiable risk factors (4). QOL refers to a person's individual perception of physical, emotional, and social status (5, 6). Patients with type 2 diabetes have a lot of stress to treat and their QOL is lower than healthy people (7, 8). Also, for chronic diabetics, complete cure cannot be achieved and clinical interventions can provide a good estimate of disease control, but the ultimate goal of diabetes care is to prevent the patient's QOL from worsening (3). It is important to understand the predictors and identify risk factors for QOL, and these factors may be targeted for prevention (5). Since the improvement of QOL is one of the important goals of treatment of diabetic patients (3, 10) and studies have shown that diabetes can have negative effects on physical function, development of complications, mental and psychological and personal, family and social relationships (15, 16); Therefore, understanding the factors related to QOL is of particular importance in the treatment programs of these patients (5). Cardiorespiratory endurance is one of the health-related physical fitness factors (2). Cardiorespiratory endurance is defined as the ability of the circulatory and respiratory systems to supply oxygen during physical activity and is usually defined as the maximum oxygen consumption (VO2max) during submaximal or maximal tests. The main determinants of VO2max are cardiovascular function, cardiac output, pulmonary diffusion capacity, oxygen carrying capacity, liver function, and other environmental constraints such as muscle diffusion capacity, mitochondrial enzymes, and capillary density, all of which are examples of determinants. Are VO2max (2, 21). VO2max is associated with functional capacity and human function and has been shown to be a strong and independent predictor of mortality from all specific causes and diseases (22). Physical activity and the resulting cardiorespiratory fitness are associated with several health benefits, including reduced risk of diabetes, cardiovascular complications, and mortality (23). In view of the above, cardiorespiratory fitness is a variable related to mortality prediction and as a health-related variable in diabetic patients (23); Therefore, cardiorespiratory fitness can be considered in determining the strategies of primary and secondary prevention programs of cardiovascular diseases in patients with type 2 diabetes; Considering the importance of factors related to the prediction and identification of risk factors for QOL (5); It is necessary to measure the relationship between cardiorespiratory fitness as a health-related physical fitness variable with QOL in patients with type 2 diabetes. In view of the above, the aim of this study was to investigate the relationship between QOL and cardiorespiratory endurance in patients with type 2 diabetes.

In this cross-sectional correlational study, 150 patients with type 2 diabetes mellitus were randomly selected from patients that had referred to health centers in Zabol city, which included 75 women and 75 men. QOL, demographic characteristics and history of diabetes in patients were measured using a questionnaire. Blood variables were measured on an empty stomach. Cardiorespiratory fitness was also measured using the Tecumseh step test. Pearson correlation coefficient was used for statistical analysis.

There was a positive and significant relationship between cardiorespiratory endurance and QOL in patients with type 2 diabetes. There was also a significant negative relationship between cardiorespiratory endurance with glycemic control, age and history of type 2 diabetes.

In the study of the relationship between cardiorespiratory endurance and QOL, the results showed that there was a positive and significant relationship between cardiorespiratory endurance and QOL in patients with type 2 diabetes. In a study of patients with type 2 diabetes, Leite et al. (2009) reported that a decrease in VO2max is associated with impaired insulin sensitivity, and that the most common abnormality in the population is at risk for insulin resistance and type 2 diabetes, and a decrease in VO2max is one. Is an important risk factor for disease progression (28). Low resting heart rate and VO2max are associated with a reduction in cardiovascular events (29). Cardiorespiratory disorders are more common in diabetic patients and may partly explain the morbidity and mortality in these patients. There are several potential causes for dysfunction in diabetics: hyperglycemia, insulin resistance, endothelial dysfunction, inflammation, microvascular dysfunction, myocardial dysfunction, and skeletal muscle changes. These changes are somewhat reversible, and improvement in each of these components may increase functional capacity in diabetic patients (30). Interventional studies indicate an increase in VO2max in adaptation to exercise in patients with type 2 diabetes (2, 31, 32). It can be said that with increasing cardio-respiratory endurance, the level of health increases and with increasing health, patient satisfaction with treatment and satisfaction with QOL improve (27). Also, The results of the present study showed that there was a significant negative relationship between aerobic fitness and HbA1c levels in patients with type 2 diabetes. Jekal et al. (2010) in a study that examined aerobic fitness and HbA1c levels, stated that people with higher cardiorespiratory fitness had better weight and lower HbA1c levels than people with lower endurance (25), which It was consistent with the results of the present study. Abushamat et al. (2020) also stated in their research that diabetes leads to decreased cardiorespiratory function, which is associated with poor glycemic control and its complications (35). Physical activity is effective in controlling blood glucose in diabetics; because it increases insulin sensitivity and glucose tolerance and decreases the level of hyperglycemia in these patients (36). Adaptations in insulin signaling as well as insulin receptors can lead to better blood glucose uptake by muscles. Increasing the number of GLUT4 carriers and increasing muscle mass, which plays a major role in blood glucose uptake, increases the body's response to insulin (38). The results of the present study also showed that there was a significant negative relationship between aerobic fitness and history of diabetes in patients with type 2 diabetes. Hadipoor et al. (2014) also introduced the years of diabetes as one of the factors affecting the physical dimension and QOL of these patients (45). Due to the fact that type 2 diabetes is associated with aging (46) and also the complications of diabetes, including cardiovascular complications with a history of diabetes and poor glycemic control are increased (47); with an increased history of diabetes, it reduces cardiorespiratory endurance in these people. On the other hand, due to having an active lifestyle and higher level of physical fitness, in addition to controlling blood sugar, the potential benefits of physical activity on reducing the complications of diabetes can be enjoyed (44, 50), which can improve QOL in patients with Type 2 diabetes is effective (50, 51). Overall, the results of our study showed that cardiorespiratory fitness was associated with improved QOL in patients with type 2 diabetes, which was negatively associated with age, duration of diabetes, and HbA1c levels.