Department of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
BMC Public Health. 2013 May 31;13:530. doi: 10.1186/1471-2458-13-530.
Incidence and prevalence of ulcerative colitis follow a north-south (latitudinal) gradient and increases northwards at the northern hemisphere or southwards at the southern hemisphere. The disease has increased during the last decades. The temporal trend has been explained by the hygiene hypothesis, but few parallel explanations exist for the spatial variability. Many factors are linked to latitude such as climate. Our purpose was to investigate the association between variables governing the climate and prospectively identified patients.
In this study, we used a subset of the population-based Cohort of Norway (n = 80412) where 370 prevalent cases of ulcerative colitis were identified through self-reported medication. The meteorological and climatic variables temperature, precipitation, and altitude were recorded from weather stations of the Norwegian Meteorological Institute. Summer temperature was used to capture environmental temperature.
Summer temperature was significantly related to the prevalence of ulcerative colitis. For each one-degree increase in temperature the odds for ulcerative colitis decreased with about 9% (95% CI: 3%-15%). None of the other climatic factors were significantly associated to the risk of ulcerative colitis. Contextual variables did not change the association to the prevalence of ulcerative colitis.
The present results show that the prevalence of ulcerative colitis is associated to summer temperature. Our speculation is that summer temperature works as an instrumental variable for the effect of microbial species richness on the development of ulcerative colitis. Environmental temperature is one of the main forces governing microbial species richness and the microbial composition of the commensal gut flora is known to be an important part in the process leading to ulcerative colitis.
溃疡性结肠炎的发病率和患病率呈南北（纬度）梯度分布，在北半球向北增加，在南半球向南增加。在过去几十年中，这种疾病一直在增加。这种时间趋势可以用卫生假说来解释，但对于空间变异性，几乎没有平行的解释。许多与纬度相关的因素都与气候有关。我们的目的是调查控制气候的变量与前瞻性确定的患者之间的关系。
在这项研究中，我们使用了基于人群的挪威队列的一个子集（n=80412），其中通过自我报告的药物治疗确定了 370 例溃疡性结肠炎现患病例。气象和气候变量温度、降水和海拔高度由挪威气象研究所的气象站记录。夏季温度用于捕捉环境温度。
夏季温度与溃疡性结肠炎的患病率显著相关。温度每升高一度，溃疡性结肠炎的患病几率就会降低约 9%（95%CI：3%-15%）。其他气候因素与溃疡性结肠炎的风险均无显著相关性。背景变量并未改变与溃疡性结肠炎患病率相关的关系。
目前的结果表明，溃疡性结肠炎的患病率与夏季温度有关。我们推测，夏季温度可能是微生物物种丰富度对溃疡性结肠炎发展影响的工具变量。环境温度是控制微生物物种丰富度的主要因素之一，而共生肠道菌群的微生物组成是导致溃疡性结肠炎的重要过程之一。
