Apparent Temperature and Inflammatory Markers in a European Panel Study

Abstract

SAA4-PD-06 Introduction: Inflammatory marker levels have been associated with cardiovascular risk, but the effect of climatologic variables in this relationship is not well understood and appreciated. Studies have shown an increase of fibrinogen in winter whereas C-reactive protein (CRP) has not been shown to be seasonally dependent so far. The objective of this study was to analyze the association between apparent temperature, an indicator of perceived temperature based on ambient temperature and dew point temperature, and the inflammatory markers CRP, interleukin-6 (IL-6) and fibrinogen in post-myocardial infarction (MI) patients. Methods: In a multicenter panel study of MI survivors, the 3 inflammatory blood markers were measured repeatedly (up to 8 times) within a period of 13 months. In total, 5835 blood samples in 1006 subjects were collected in 6 European cities. Data on patient characteristics and disease history were gathered at the baseline visit. Meteorologic data were obtained from the country-specific network stations. The association was analyzed using a generalized additive model with random patient effects. The model variables were selected in each city separately based on Akaike's Information Criterion and consisted of time-invariant baseline variables and long-term time trend. Different lag-structures of the apparent temperature effect were tested. For the analysis CRP and IL-6 had to be log-transformed. The effect estimates are presented as percent changes of geometric mean based on a 5°C decrease of apparent temperature. Results: Patient mean levels of CRP ranged between 0.2 and 37.4 mg/L (mean ± standard deviation: 2.6 ± 3.3 mg/L), IL-6 had a range of 0.5 and 61.4 pg/mL (3.0 ± 3.1 pg/L), and levels of fibrinogen were between 1.9 and 6.9 g/L (3.6 ± 0.7 g/L). In the preliminary analysis, the mean of the current and the previous day's apparent temperature was associated with CRP. The city-specific effect estimates were all positive except for one city. Although they ranged between −1.61% and 8.22%; no evidence for heterogeneity was observed. The pooled effect estimate was 1.52% change in CRP (95% CI, −0.03%, 3.10%) in association with a 5°C decrease in apparent temperature. The effects on IL-6 and fibrinogen were heterogeneous between the cities and therefore not pooled. Discussion and Conclusions: The results suggest that a decrease in apparent temperature leads to an increase in CRP level. In susceptible patients, this might lead to an additional risk for cardiovascular events and provides a hint for the observed seasonal variation in death from ischemic heart disease and stroke in the elderly.