To Örebro University

Background: Eventual differences of expiratory nitric oxide (F_ENO) levels in general populations of Nordic countries may reflect differences in eosinophilic inflammation at population level.

Aim: To study the differences in F_ENO of Nordic regions and their epidemiological associations.

Methods: From 1997 to 2003 we measured F_ENO (ppb) and conducted skin prick-tests for a random sample of adults (n=1498), aged 20-60 years from Finland (Helsinki), Sweden (Stockholm and Örebro) and Estonia (Narva and Saaremaa). We compared differences between regions by estimating odds ratios (OR) and 95% confidence intervals (CIs) for high F_ENO (>25 ppb) using logistic regression adjusted for gender, smoking and allergy. Finally, we estimated crude ORs and 95% CIs for high F_ENO and for asthma, rhinitis, current asthma symptoms and asthma medication.

Results: The mean and standard deviation (SD) for F_ENO was 19(14) in Finland, 18(12) in Sweden and 16(15) in Estonia (p<0.001). Estonia had a lower mean F_ENO than other countries, with no differences between Finland and Sweden. Compared to Helsinki, the adjusted OR (95%CI) for high F_ENO was 0.42(0.21-0.81) in Stockholm, 0.65(0.43-0.98) in Örebro, 0.53(0.32-0.84) in Narva and 0.45(0.28-0.71) in Saaremaa. In Estonia, high F_ENO was associated with asthma, allergy, rhinitis, current asthma, and asthma medication; in Finland with rhinitis and use of short acting β-agonist; in Sweden with asthma and asthma medication. Smoking was associated with low F_ENO. Mean F_ENO in asthmatics was 24(19) in Finland, 20(12) in Sweden, and 43(49) in Estonia (p=0.07).

Conclusions: We observed a higher mean F_ENO in Finland and Sweden compared to Estonia, and found no overall differences of F_ENO levels in asthmatics.