Research on the Effects of Hot Temperatures on Health in Catalonia

Writing for the Mediterranean City Climate Change Consortium newsletter seems a very appropriate task while seated just a few meters from the Mediterranean Sea and suffering the heat of a summer with record-breaking temperatures. In this post, I will summarize some of the research linking temperature and health we have conducted in the Center for Research in Environmental Epidemiology (CREAL) in Barcelona, Spain.

Many of our studies have focused on the city of Barcelona or on the Catalonia region. For example, in a comprehensive analysis of mortality and heat we calculated that, in Catalonia, mortality increases by 19% after three consecutive extremely hot days  Interestingly, around 40% of the deaths attributable to heat did not occur during heat wave periods according to the most commonly used definitions. In the same study, we were able to detect an increase of 25% in the risk of infant mortality in days of extreme heat. Although infant mortality is low in developed countries such as Spain, this increased risk, which was restricted to the first week of life, confirms that newborns are especially susceptible to the effects of high temperatures. As has been shown in several other parts of the world, the number of deaths attributable to heat is expected to increase substantially in the future in Catalonia, not only because of the increasing temperatures but also because of the aging population.

In terms of heat-related mortality, we have also addressed within-city disparities in risk. We detected that, in the city of Barcelona, some areas can have up to twice as much risk of heat-related mortality than others. Even though we had a limited number of area-level variables to investigate, the areas having the higher risks were those with a higher percentage of manual workers, those with more people perceiving little surrounding greenness and those with a large percentage of old buildings. This suggests that factors such as socioeconomic status can play a role in modulating the risk of heat-related mortality. Increasing greenness can also alleviate the health effects of heat, as it is known to reduce surface temperatures and prevent the heat island effect. However, in our study the variation in risk was not related to objective measures of greenness, but only to subjective ones. Those subjective measures could be capturing other forms of environmental degradation. Finally, the variable on old buildings may suggest that the stock of old buildings in the city may have lower levels of thermal insulation and a lower heat dissipation capacity.

Apart from the more traditional studies of heat and mortality, we addressed other health outcomes that also show an association with heat. For example, we found that increased temperature and high humidity levels during weeks 32-36 of pregnancy were associated with an increased probability of group B streptococci (GBS) colonization. GBS colonization does not imply the development of GBS invasive infection, although it increases its risk and can increase the risk of early-onset neonatal sepsis. In another study, we found that extreme heat episodes were followed by births with reduced length of gestation. Specifically, there was an average 5-day reduction in gestational length in extremely hot days. Although the mechanisms for this association are not fully elucidated, several biological mechanism link heat stress to labor induction in humans.

One of our most recent studies has shown that there is an increased risk of traffic accidents in days with high temperatures, especially for accidents involving driver performance (namely, those involving distractions, driver error, fatigue or sleepiness). This is consistent with several experimental studies that showed that drivers in a hot environment make more technical errors, show an increased tendency to drift out of the lane, make more large steering adjustments, miss more signals and report more fatigue. It is known that high temperatures decrease our capability of performing physical and intellectual tasks, and this mechanism is also speculated to be the reason for the increase in work-related injuries associated to high temperatures.

These studies exemplify how the health sector can be a key driver in promoting actions for climate change mitigation and adaptation.

About the Author:  Dr. Xavier Basagaña is Assistant Research Professor at the Centre for Research in Environmental Epidemiology (CREAL) in Barcelona, Spain. He earned a BSc (1999) and a MSc in Statistics (2002) from Universitat Politècnica de Catalunya (UPC), and a PhD in Biostatistics from Harvard University (2007). Dr. Basagaña worked as a statistician in the Respiratory and Environmental Research Unit in the Municipal Institute of Medical Research (IMIM) in Barcelona from 1999 to 2003, and joined CREAL in 2008 as an Assistant Research Professor in Biostatistics. His interest focuses on several statistical methods to draw valid inferences from observational data. Currently, his research is mainly focused on the design and analysis of observational longitudinal studies, measurement error correction methods, spatial statistics, non-response and missing data methods, and multilevel models.