It has been well documented that temperature variability within a short period (e.g., DTR and TCN) affects human health among children [15-17]. We carried out a standard time-series study to examine the effects of DTR and TCN on childhood AR in Hefei, China. We found that temperature drops between two days (TCN < 0) increased the risk of childhood AR. This risk was greater among boys, children ≥15 years and students. However, significant effect of DTR was not observed.
The association between temperature and AR was examined in several recent studies, consistently showing an adverse effect of cold weather on AR in many countries such as Korea, China and Finland [12-14]. However, it still remains unknown whether or not the risk of AR could be influenced by unstable weather, i.e., DTR or TCN. In this contribution, we used a standard time-series analysis to explore the association between childhood AR and temperature variability. Relevant findings provide support for our hypothesis that there is a connection between TCN and AR in children. Similarly, some previous studies also reported adverse effect of short-term temperature variability. For example, Xu and colleagues found the risk of childhood asthma increased above a DTR of 10°C [17-18] reported a 1.0% increase of childhood acute bronchitis cases per 1 C increment of DTR. The present study further revealed that temperature variability had adverse effects on childhood AR.
Although DTR and TCN have been widely used in previous studies, litter is known about the relative effects of these two temperature variability indictors. To our knowledge, only one study has evaluated the health risk of DTR and TCN among children . This study was conducted in Brisbane, Australia, which found significant association of childhood pneumonia with TCN, not DTR. The present study also suggested that the risk of AR among children was particularly vulnerable to the effects of TCN, rather than DTR. These findings probably imply that more attention paid to the temperature change between two adjacent days could help reduce the negative health consequences of unstable weather among children.
We also observed that TCN had the largest effect one week later, namely at lag 12 (Table 2). One possible reason for the observed delayed effects of TCN is that, after exposure to temperature variability, our thermoregulatory center and immune system will be involved to eliminate or alleviate the harmful health effects of temperature. Few days later, when temperature effects exceed the limit that our proactive defense can handle, some respiratory diseases could occur such as allergic rhinitis as well as childhood pneumonia as reported previously . Another reason could be related to the delayed effects of TCN on the dehydration of pollen, which is the trigger of allergic rhinitis. Nevertheless, more research is needed to explore the mechanism for the delayed effects of temperature variability.
Stratified analyses by gender revealed that boys were more likely to be influenced by TCN than girls. In general, boys have more outdoor activities than girls, which may expose them more often to outdoor environment change such as temperature drops, increasing the possibility of AR infection. Stratified analyses by age suggested that children aged 15 year or above and in-school children (i.e., students) were more vulnerable to TCN. This result contradicts with our commonsense that, compared with old children, younger children are more vulnerable to temperature effects, because younger children are relatively under-developed and have less self-care ability . Therefore, more research is needed to prove our findings in other regions.
This study has some strengths. To be best of our knowledge, this is the first study to date investigating the association of AR with short-term temperature variability. Our findings thus add new evidence to the existing literature of temperature and AR. In the preset study, temperature variability was measured by DTR and TCN; these two temperature indictors were often employed by previous researchers to evaluate the effect of unstable weather on human health [16, 19]. Our results regarding the comparison of the effects of DTR and TCN will help us to know that the major threat of temperature variability to AR occurrence is from sudden temperature drop between two adjacent days. We were also able to perform stratified analyses by age, gender, occupation; relevant findings will be useful for guiding the prevention of AR occurrence from the adverse effect of temperature. Limitations of this study should be also acknowledged. First, this study was conducted in a single city, which limits the generalization of our findings to other regions with distinct city characteristics such as climate and socioeconomic status. Second, similar to previous study, we used the mean temperature to measure the exposure of temperature among children, which to some extent caused some biases [16, 19]. Besides, many other confounders such as airborne pollen are risk factors of allergic rhinitis have not been considered in our data analysis. The effects of TCN may be attenuated after including more confounders in the data analysis. Third, this is an ecological study, which cannot prove the causal association between temperature variability and AR. Fourth, the type of allergic sensitization (pollen, mold, and mites) play an important role in influencing the association between environmental risk factors and allergic rhinitis. Equally important is the usage of medicine among patients with allergic rhinitis. Therefore, the association between temperature variability and allergic rhinitis could be modified by the type of allergic sensitization (pollen, mold, mites) as well as some medicines for treating allergic rhinitis. However, we were unable to conduct such stratified analyses in the present study because the relevant data were not available.