Metabolic responses to physical activity in subjects with type 1 diabetes

Abstract

Type 1 diabetes mellitus is an autoimmune chronic disease that has undergone drastic changes on its clinical natural history in the last decades.

Until the early XX century, the diagnosis of diabetes would mean a fatal outcome in few weeks or months. The evidence of hyperglycemia associated with abrupt polyuria, polydipsia, polyphagia and weight loss in a child or a young person determined a diagnosis of failure of insulin secretion, metabolic catabolism and death.

The introduction of treatments with exogenous insulin was the first important change in the natural clinical history of diabetes. Subjects affected by diabetes experienced then a hope of treatment and life. The main initial concern of physicians and scientists was to avoid important episodes of hypo or hyperglycemia, which could lead to hypoglycemic coma or diabetic ketoacidosis. Different classes of insulins were tested and used with success, offering better life expectancy for the affected persons.

In parallel with the provided increase of life expectancy, chronic complications related to diabetes were prone to appear. Those patients who, at that moment, benefit from the exogenous insulin, but maintained many episodes of hyperglycemia and glycemia fluctuations, developed chronic complications leading to blindness, renal failure, limbs amputations and/or cardiovascular complications as heart attack or stroke.

Aware of the consequences of hyperglycemia, researchers started to design studies promoting a more strict control of glucose levels, with the intention of minimizing chronic complications related to diabetes. Studies for type 1 diabetes (T1D) like DCCT, published in 1993 (The Diabetes Control and Complications Trial Research Group, 1993) and its follow-up EDIC (Nathan et al., 2005), and others alike for type 2 diabetes (T2D) (UK Prospective Diabetes Study, UKPDS Group 1998), proved the reduction of complications rates and marked a new change in the natural clinical history of diabetes.

Recently, tighter glycemic control became possible with the help of new insulins, insulin infusers, glucose sensors and nutrition research. The incidence of retinopathy, nephropathy, neuropathy and their consequent serious outcomes as blindness, end renal stage disease and lower limb amputations, reduced in the past two decades, as described in the US patients with diabetes (Gregg et al., 2014). The excess risk of mortality in individuals over 20 years old with diabetes (T1D and T2D) if compared with the risk of individuals without diabetes has decreased over time in both Canada and the UK, as shown in data recently published (M Lind et al., 2013). This may be, in part, due to the earlier diagnosis, as well as to improvements in diabetes care (M Lind et al., 2013). In patients with T1D, a reduction of all-cause mortality and also of specific cardiovascular mortality could be verified, especially if associated with a good glycemic control; these rates, nevertheless, are still the double of the ones seen in subjects without diabetes (Marcus Lind et al., 2014).

Physical activity is considered as a health promoter procedure for general population and a therapeutic tool for prevention and/or treatment of several chronic diseases, like T2D, cardiovascular disease or cancer. Persons with T1D are stimulated to participate in exercise training programs and competition events. Nowadays, with the current knowledge, several elite athletes with T1D are able to compete in the same categories that the ones without diabetes, but requiring for that a strict balance among insulin adjustments, carbohydrate intake and physical activity characteristics.

Many questions may be formulated at the present time: are persons with T1D being beneficiated from physical activity as persons without diabetes? Do the subjects with T1D present the same physical conditions for exercise performance than the non-diabetic ones? Do they present different metabolic response when performing a session of exercise? Does physical activity improve lipoprotein profile generating cardiovascular benefits for the subjects with T1D? What are the characteristics of muscular composition of patients with T1D, and are they different from subjects without diabetes? What are the factors that could be interfering? These questions are discussed in the present thesis. Some answers were achieved and some other questions emerged. Nowadays, the availability of new technological approaches, the improvements on basic research, and the possibility to integrate the information of basic research with clinical research are improving the knowledge in biomedical science.

A better understanding of physiopathology can be obtained, and with it, a better care, a better quality of life, and longer life expectancy can be offered to persons who have type 1 diabetes.