Respiratory symptoms and asthma in relation to cold climate, inhaled allergens, and irritants: a comparison between northern and southern Finland.

We have compared data from northern and southern Finland in a large epidemiological survey on respiratory conditions. The aim was to compare the prevalence of respiratory symptoms, asthma, and chronic bronchitis in northern and southern Finland. The study was a part of comparative studies in Finland, Estonia, and Sweden, the FinEsS studies. Data from a postal survey on subjects aged 20-69 was analyzed. Participation rate was 84% of 7937 invited in Lapland in the north, and 77% of 7877 in Helsinki in the south. Physician-diagnosed asthma was reported by 5.6% in Helsinki, and by 5.5% in Lapland. Symptoms common in asthma were also equally prevalent in the two areas. Hay fever was significantly more common in Helsinki, 36% vs. 26% (p < 0.001). The prevalence for physician-diagnosed chronic bronchitis was not significantly higher in Helsinki (3.4%) than in Lapland (2.9%). Those working outdoors reported more bronchitic symptoms than people working indoors (p < 0.05). Respiratory symptoms provoked by pollen or animal dander were more common in Helsinki, while symptoms provoked by inhaled irritants or cold weather conditions were more prevalent in Lapland. Current smoking was equally prevalent: 37% in Lapland and 38% in Helsinki. Risk factor analysis showed an elevated risk for chronic productive cough for living in Helsinki (OR 1.32), however, increasing age and current smoking were the strongest risk factors. In conclusion, prevalence of asthma and asthma-related symptoms was similar in southern and northern Finland, but chronic bronchitis and bronchitic symptoms were more common in Helsinki, and the highest prevalence was found among current smokers working outdoors. Respiratory symptoms in cold weather were more prevalent in the north, while hay fever and respiratory symptoms provoked by allergens were more common in the south. The results support the view that environmental factors have a substantial effect on respiratory symptoms, but less effect on the prevalence of asthma.