Below-Average Temperatures During Winter Linked to Increased Risk of Asthma

“Environmental exposures, such as cold air or air pollution, may trigger symptoms or exacerbation of asthma. There is also evidence that long-term exposure to air pollution increases the risk of developing new asthma,” a team of researchers wrote in a recent study. Therefore, they investigated the relationship between cold winters and the risk of developing asthma during the following 1 to 2 years.

Their study was published in Occupational & Environmental Medicine.

The case-control study analyzed 315 newly diagnosed cases of asthma in Finland. These cases were drawn from the population-based Espoo Cohort Study, which followed individuals from birth to the age of 27 years.

The hazard period considered the 3 winter months leading up to the onset of asthma, and bidirectional reference periods were used (1 year before the hazard period and 1 year after the asthma diagnosis). The exposure variable in question was the average ambient temperature during the winter months, specifically December, January, and February. The primary outcome of interest was the incidence of new doctor-diagnosed asthma. The researchers calculated the odds ratio (OR) of developing asthma using conditional logistic regression analysis.

Over the study period, from the winter of 1983 to the winter of 2010, the average winter temperature was −4.4°C, with a range of −10.7°C to 0.4°C. Notably, the results showed that for each 1°C decrease in the average winter temperature, there was a 7% increase in the risk of developing new asthma (OR, 1.07; 95% CI, 1.02-1.13). The most striking discovery, however, was that a particularly cold winter, with an average temperature below the climate’s normal value (−4.5°C, as determined for the period of 1981 to 2010), increased the risk of developing asthma by a substantial 41% during the following year (OR, 1.41; 95% CI, 1.04-1.90).

Evaluating the results of their study, the investigators concluded that the combined impact of cold winters on asthma could involve a combination of frigid temperatures and changes in environmental conditions and human conduct.

“Although long-term exposure to cold weather is a biologically plausible cause of asthma, we cannot exclude the possibility that other environmental exposures related to a cold winter, such as an increase in ambient and indoor air pollution due to increased heating using fossil fuels, could contribute to the increased risk of asthma,” they concluded.