In patients with rheumatoid arthritis, exposure to air pollution is associated with both elevated levels of C-reactive protein (CRP) and increased risk of arthritis flares, according to a novel longitudinal study presented at the annual European Congress of Rheumatology.
Dr. Giovanni Adami
The data revealed “a striking association between air pollution and increased CRP levels and risk of an arthritis flare,” reported first author Giovanni Adami, MD, DSc, of the rheumatology unit at the University of Verona (Italy).
The excess risk of elevated CRP and flares began “at very low levels of exposure, even those below commonly used thresholds for risk to human health,” he added.
Study details
Researchers collected data on 888 patients with RA from numerous patient visits in the context of more than 13,000 air pollution records. The CRP levels and RA flares were evaluated in the context of air pollution monitoring that is performed on a daily basis at several sites in the city of Verona where the study was conducted. Verona is an industrial city in northern Italy that has high but variable levels of air pollution based on factory activity and weather conditions.
Patients with RA who provided clinical data for this study were matched by their proximity to specific air pollution monitoring sites. By linking CRP levels and disease activity to air pollution levels over multiple follow-up visits, the design allowed the RA study participants “to serve as their own controls,” Dr. Adami explained.
At each patient visit during the study, CRP levels were measured and disease activity assessed. Patients were considered to have elevated CRP when levels were 5 mg/L or higher. The presence of an RA flare was defined by a 1.2-point increase or more in 28-joint Disease Activity Score using CRP (DAS28-CRP).
Both the CRP level and the presence or absence of a flare were evaluated in relationship to the patient’s specific local air pollution levels in the prior 60 days.
Increased levels of CRP, a surrogate for inflammatory activity, and increased disease activity, were both associated with elevated exposure to air pollutants prior to an office visit. These associations remained statistically significant when evaluated by specific air pollutants such as carbon monoxide (CO), nitrogen oxides (NO2, NO), small particulate matter (PM10; particles ≤ 10 mcm), and ozone (O3).
The relationship between increased exposure to air pollution contaminants and elevated CRP was supported by a dose effect. In the case of PM10, for example, the odds ratio of having elevated CRP was increased by only about 25% (OR, 1.25) when mean levels were 30 mcg/m3 or lower in the period prior to the office visit. This rose incrementally for higher mean levels of PM10, reaching 70% (OR, 1.70) for levels > 50 mcg/m3.
The researchers detected statistically significant differences in mean and area-under-the curve (AUC) values of most air pollutants in the 60 days prior to office visits when patients had a flare versus when disease activity was low. For example, the difference in mean and AUC levels in the period prior to a flare relative to a period with low disease activity was significant for CO (P = .001 for both) and NO and NO2 (P = .003 for both), and O3 (P = .002 and P = .001, respectively). For PM10, P values were .011 and .005, respectively.
“Remarkably, we found that the cumulative exposure to NO2 in the 60 days preceding a flare was approximately 500 mcg/m3 higher than the low disease activity visit, an exposure that equates to approximately 200 passively smoked cigarettes,” Dr. Adami reported.