| dc.description.abstract | Patients with rheumatoid arthritis (RA) have higher mortality rates than the general population as well as lower cardiorespiratory fitness. They also have an increased risk of myocardial infarction of similar magnitudes as patients with diabetes. Prior to this thesis, mortality in RA and diabetes had not been directly compared in a longitudinal populationbased setting. Moreover, as improving or maintaining physical fitness is important for longterm health, further insight into factors associated with physical fitness in RA patients may inform clinical practice and the development of intervention programmes.
We wanted to investigate whether RA patients had higher mortality rates and lower physical fitness compared to controls, and identify factors associated with physical fitness in RA patients.
We used data from the population-based Trøndelag Health Study linked to the Norwegian Cause of Death Registry for Study I. Cox proportional hazard regression was applied to compare mortality rates in patients with RA, patients with diabetes, and controls. We also compared the distribution of deaths due to diseases of the circulatory system, neoplasms, and diseases of the respiratory system.
To investigate factors associated with physical fitness, we recruited RA patients and healthy controls. The distance walked during a 6-minute walk test and the cardiorespiratory fitness estimated from non-exercise formulas were used as physical fitness measures. Study II applied multivariable linear regression to explore factors associated with the distance walked during the 6-minute walk test. We used Pearson’s correlation coefficient and a scatterplot to assess the relationship between walk test distance and estimated cardiorespiratory fitness. Study III applied structural equation modelling to evaluate whether more physical symptoms and negative emotions could explain the association between RA status and reduced estimated cardiorespiratory fitness.
Study I included 387 RA patients, 2,898 diabetes patients, 33 patients with both diseases, and 63,903 controls. Median follow-up time was 18 years. When taking age, sex, smoking, body mass index, hypertension, creatinine, total cholesterol, and previous cardiovascular disease into account, RA patients and diabetes patients had higher mortality rates than controls. Compared to the controls, RA patients had 24 % higher mortality rates in the adjusted models. The corresponding estimates for diabetes patients ≤75 years and >75 years were 83 % and 49 % higher mortality rates than controls, respectively. The distribution of death causes in the RA patients was not statistically significantly different from the distribution in diabetes patients or controls.
Study II included 79 RA patients. Age, body mass index, smoking habits, patient global assessment, and self-efficacy for exercise were associated with how far the participants walked during the 6-minute walk test. Moreover, the fitness measures distance walked during the 6-minute walk test and estimated cardiorespiratory fitness were significantly correlated (r=0.61, p<0.0001). Study III included 227 RA patients and 300 controls. RA patients had on average 1.7 mL/kg/min lower estimated cardiorespiratory fitness than controls when taking age and sex into account (p=0.002). Higher prevalence of physical symptoms and negative emotions explained 74 % of the relationship between RA status and lower estimated cardiorespiratory fitness.
This thesis demonstrated that RA patients had higher mortality rates and lower estimated cardiorespiratory fitness than controls. Higher prevalence of physical symptoms and negative emotions could explain a large proportion of the difference in estimated physical fitness between RA patients and healthy controls. It is therefore extremely important to address lifestyle, physical fitness, and mental health in addition to pharmacological treatment to improve long-term health among RA patients. We also identified several patient-reported measures associated with physical fitness. These measures are tools that can be useful in clinical practice and in exercise interventions. Together with some measure of physical fitness or physical activity, these tools may help to identify patients who would benefit from extra follow-up. | en_US |
