Physical activity and type 1 diabetes : impact on diabetic complications

Background: Type 1 diabetes is a chronic condition with risk of severe long-term complications (cardiovascular disease, diabetic nephropathy, neuropathy and retinopathy) that increase the risk of premature mortality, reduce quality of life and cause a huge economic burden to society. The main cause of death and inability in individuals with type 1 diabetes are cardiovascular events, and it has been shown that diabetic nephropathy is the main driver of the increased risk of cardiovascular morbidity and mortality. Diabetic retinopathy is the leading cause of vision loss and blindness in developed countries. Physical activity has been shown to improve the risk profile of individuals with type 1 diabetes. Consequently, previous cross-sectional data show that lower physical activity is associated with a higher degree of diabetic complications, but the causal relationship is unclear. Aim: The aim of this thesis is to assess how the total amount of leisure-time physical activity (LTPA) and its components of intensity, frequency and duration are associated with the development of diabetic nephropathy, cardiovascular outcomes, diabetic retinopathy and mortality in type 1 diabetes. Subjects and methods: The study subjects of this thesis are participants in the ongoing nationwide, multi-centre Finnish Diabetic Nephropathy (FinnDiane) Study. Currently, more than 5000 individuals with type 1 diabetes have been recruited and thoroughly characterized from all over Finland. LTPA was assessed at baseline by a validated self-report questionnaire. The study design is prospective and observational. Results: The intensity of LTPA was associated with the initiation and progression of diabetic nephropathy. Of the other LTPA components, frequency was also associated with the progression of diabetic nephropathy. A larger amount of total LTPA and its components were associated with lower risk of CVD events during follow-up. Only the association between LTPA frequency and incident CVD remained significant after adjustment for potential confounders. LTPA and all its components were associated with lower risk of all-cause mortality after adjusting for several confounders. However, only the LTPA intensity was associated with cardiovascular death after adjusting for covariates. Also, total LTPA and frequency of LTPA were independently associated with lower risk of mortality in individuals with type 1 diabetes and chronic kidney disease. In addition, frequent LTPA was associated with lower risk of severe diabetic retinopathy. Conclusions: Physical activity was associated with reduced risk of diabetic complications and mortality in individuals with type 1 diabetes. In addition, physical activity also seems to benefit those with diabetic complications – notably, diabetic nephropathy – and appears to be safe.