Impact of psychosocial factors on rheumatoid arthritis

Sammanfattning: In the field of rheumatology, the research has been successful in the understanding of the molecular mechanisms of the underlying pathophysiology of rheumatoid arthritis (RA). As a result of this, targeted treatments have been developed, resulting in a dramatic improvement of disease outcome. Today, there is an ongoing work aiming for treating the disease in very early stage or even preventing the disease. However, the exact etiology for RA is not fully known and previous epidemiological research has indicted that contextual factors contributes to both the risk for disease and the development of structural joint damage. The aim of this thesis is to contribute to the understanding of how external factors, in particular socioeconomic characteristics, associate to the risk for developing, the onset of and the severity of rheumatoid arthritis. In study I, a case-control study within the Swedish Epidemiological Investigation of Rheumatoid Arthritis (EIRA), we investigated if low social support and low decision latitude at work, respectively, were associated with risk for RA. Further we investigated whether those two exposures were associated with other previously identified risk factors for disease. We retrieved information on social support from the EIRA I+II study (3724 cases and 5935 controls) and information on decision latitude at work from the EIRA I study (1998 cases and 2252 controls). We did not observe any association between low social support and risk for RA (OR 1.00 (95% CI 0.91– 1.11) in the multivariable model) as compared to not low social support. Nor did we observe any statistically significant association between low decision latitude at work and RA (OR 1.28 (95% CI 0.96–1.71) in the multivariable model) as compared to high decision latitude. Both investigated exposures were associated with smoking and low educational level but neither of them were associated with disease specific characteristics such as ACPA- or RF-status. In study II we analyzed the association between alcohol habits and the risk for development of RA and furthermore if there was an interaction with smoking. We retrieved information on alcohol- and smoking habits from the Swedish National March Cohort (n=41 068). Information on the outcome, i.e. incident RA, was obtained from the national patient register. During the follow-up time 577 individuals developed RA. We observed that overall, alcohol consumption was associated with a 30% reduced risk of RA (HR 0.69, 95% CI 0.55-0.86). The negative association between alcohol consumption and RA risk was more pronounced among smokers. We observed a statistically significant interaction between smoking and alcohol habits with an attributable proportion of 0.4. In study III we investigated whether low social support and low decision latitude at work, respectively, were associated to RA disease remission. Information on exposures was retrieved from the EIRA study and information on outcome, that is disease activity at 3, 12 and 60 months follow up, was captured from the Swedish Rheumatology Quality Register (SRQ). There were 2820 individuals with information from both EIRA and SRQ. In this study low social support was not associated with remission rate at any of the investigated time-points, as compared to not low social support. Low decision latitude at work was not associated to remission at any of the investigated time-points, compared to not low decision latitude at work. Our studies have contributed to the understanding of the impact of external factors on both disease risk and disease course in RA.