Page 54 - THE EVOLUTION OF EARLY ARTHRITIS AND CARDIOVASCULAR RISK Samina A. Turk
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CHAPTER 3
Besides obesity several other comorbidities have since long been linked to the development of RA, such as diabetes mellitus and schizophrenia. Recently, two other diseases have been investigated. Sleep disorders (without sleep apnea) had an HR of 1.45(39) and autoimmune thyroid disease was seen more frequently in RA cases than in controls (together with more thyroxin substitution before RA development)(40).
The exact mechanism as to how systemic autoimmunity advances into local inflammation in the joints still needs to be further investigated(7). It is thought that infections may trigger the onset of clinically apparent disease. Some recent publications have focused on the presence of infections before RA onset and specific pathogens. Prior infection-related medical visits and bacterial colonization are shown to predispose the development of RA, mostly in the year preceding diagnosis(41, 42). However, another study found a decreased risk of gastrointestinal and urinary tract infections and no relation for other infections(43). So far, no specific pathogen could be quantitatively linked to RA development(6). Regarding the related subject of vaccination, only one out of many studies reported an increased risk <1 year after tetanus vaccination(44).
Finally, de Roos et al. investigated living in the proximity to traffic, ambient air pollution, and community noise. They found a higher risk of RA when living within 50 m from the highway (OR 1.37), but they could not relate this to ambient air pollution or noise(45). In this study, it is good to note that it was not possible to correct for confounding factors such as low social economic status, nonwhite race, and smoking. Therefore, the results may be biased. Besides, another study could also not find a relationship between air pollution and the development of RA(46).
A distinction was made between traditional risk factors, meaning generally accepted risk factors before at least 4 years ago (most already presented in previous edition of Best Practice & Research), and the ones receiving more attention over the past years and generating new insights.
Table 2. Environmental risk factors for development of rheumatoid arthritis
 Traditional risk factors
Validated risk factor
Family history
Female gender Ageing
Smoking
Lower education level Silica exposure
Pregnancy
Comment
65% of RA risk is thought to be heritable
Females have 2-4 times higher risk
Onset usually around sixth decade of life
One of the main risk factors, dose-dependent risk effect
Possibly linked to lifestyle or certain occupations
Industrial exposure: mining, construction, agriculture, electronics
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Increased risk in the year after childbirth
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