CityAdapt Blog – Health Impacts from Heat Exposure in California

With more frequent heat waves predicted, it is essential to study health outcomes associated with elevated temperature.  By identifying vulnerable subgroups, some heat-related deaths, illnesses, and adverse health outcomes can be prevented.  Increased temperatures were found to have same-day effects on deaths and emergency room visit admissions for several outcomes, showing the importance of acting quickly.  The following are excerpts from a few selected abstracts of my work that focus on pregnant women, infants, deaths, and emergency room visits, respectively:

The risk of preterm birth found to increase with heat exposure in California

Pregnant women may not be able to cool down when they are exposed to heat, since their thermoregulatory responses may be compromised. Uterine blood flow to the fetus typically increases during pregnancy, but with heat exposure, body temperatures may rise causing uterine blood flow to decrease, thereby causing contractions and inducing labor. In a recent epidemiologic study, Basu et al. (2010) identified almost 60,000 preterm births from the California birth registry that occurred between the warm season (May 1 through September 30), 1999 to 2006. They estimated that for every 10° Fahrenheit (°F) increase in heat and humidity, as measured by apparent temperature, an 8.6% increase (95% confidence interval (CI): 6.0, 11.3) in preterm delivery (20 to 36 gestational weeks) risk was found. Greater risks were observed for mothers who were younger, African-American, or Asian. Air pollutants did not change these results. To avoid preterm births, pregnant women should be advised to stay hydrated and avoid physical exertion especially during the warm season.

The risk of low birth weight infants for fine particle exposure in California

Relationships between prenatal exposure to fine particles (PM2.5) and birth weight have been observed previously. Few studies have investigated specific constituents of PM2.5, which may identify sources and major contributors of risk. Basu et al. (2014) examined the effects of trimester and full gestational prenatal exposures to PM2.5 mass and 23 PM2.5 constituents on birth weight among 646,296 term births in California between 2000 and 2006. The largest reductions in birth weight were associated with exposure to vanadium, sulfur, sulfate, iron, elemental carbon, titanium, manganese, bromine, ammonium, zinc, and copper over the entire gestational period. Several of these PM2.5 constituents were associated with increased risk of term LBW. Reductions in birth weight were generally larger among younger mothers and varied by race/ethnicity. Exposure to specific constituents of PM2.5, especially traffic-related particles, sulfur constituents, and metals, were associated with decreased birth weight in California.

Identifying vulnerable populations of deaths from outdoor heat exposure during the warm season in California

A total of 231,676 deaths occurring during the warm season of 1999-2003 in California were included in this study (Basu et al. 2008). Each 10°F increase in mean daily apparent temperature corresponded to a 2.6% (95% CI: 1.3, 3.9) increase for cardiovascular mortality, with the most significant risk found for ischemic heart disease. Elevated risks were also found for persons at least 65 years of age (2.2%, 95% CI: 0.04, 4.0), infants 1 year of age or less (4.9%, 95% CI: 1.8, 11.6), and African-Americans (4.9%, 95% CI: 2.0, 7.9). No differences were found by gender or educational level. To prevent deaths associated with high apparent temperature, persons with pre-existing cardiovascular disease, the elderly, infants, and African-Americans among others should be targeted. Heat-health watch programs have been developed in some cities throughout the world as prevention efforts, and most have been successful in preventing illnesses and deaths during heat waves by targeting vulnerable populations, particularly the elderly who live alone.

The effect of high ambient temperature on emergency room visits in California

In another study, over 1.2 million ER visits were included during the warm season of 2005-2008 (Basu et al. 2012). Positive associations were found for apparent temperature and isch­emic heart disease (% increase per 10°F = 1.7 [95% CI = 0.2 to 3.3]), ischemic stroke (2.8 [0.9 to 4.7]), cardiac dys­rhythmia (2.8 [0.9 to 4.9]), hypotension (12.7 [8.3 to 17.4]), diabetes (4.3 [2.8 to 5.9]), intestinal infection (6.1 [3.3 to 9.0]), dehydration (25.6 [21.9 to 29.4]), acute renal failure (15.9 [12.7 to 19.3]), and heat illness (393.3 [331.2 to 464.5]). Negative associations were found for aneurysm, hemorrhagic stroke, and hypertension. Most of these estimates remained relatively unchanged after adjusting for air pollutants. Age and race/ethnicity seemed to modify some of these impacts, with Asians and Hispanics having greater risk for some of the outcomes considered. Since cholesterol levels increase during periods of heat exposure and blood flow often diverts from the heart and other vital organs to underneath the skin’s surface in an effort to cool down, increased pressure is put on the heart, resulting in heart attacks or other illnesses. Intestinal infections may increase during the summer, particularly for children, as more time may be spent outdoors in swimming pools and picnicking. During heat waves or high heat exposure periods, it is important to not only consider heat-related deaths and illnesses, but also other outcomes that may be related to truly capture the total burden of disease.

For more information about this research, you can go to CalEPA’s Office of Environmental Health and Hazard Assessment’s (OEHHA) website.

Also, please see Dr. Rupa Basu’s appearance on the television show “Years of Living Dangerously: Mercury Rising” with Matt Damon and her lecture at the University of Southern California (“Climate Change Impacts on Public Health”):

About the Author:  Dr. Rupa Basu has extensive experience and expertise relating to the effects of temperature on human health outcomes.  Her research has used various epidemiologic methods, including the case-crossover and time-series study designs, to estimate the independent effects of temperature and air pollution on mortality, morbidity, and adverse birth outcomes, with a focus on identifying vulnerable subgroups and racial/ethnic disparities.  Dr. Basu is currently Chief of the Air and Climate Epidemiology Section at the Office of Environmental Health Hazard Assessment (OEHHA) at the California Environmental Protection Agency.  Prior to joining OEHHA, she worked at the US Environmental Protection Agency, after obtaining her PhD degree in environmental and occupational epidemiology from The Johns Hopkins University Bloomberg School of Public Health and her MPH degree with an emphasis in environmental health sciences from the UCLA School of Public Health.  She serves on several statewide and other climate change committees and has been an invited to be a guest speaker on many occasions, most recently by former Governor Schwarzenegger at USC. She will also be featured in the upcoming documentary, “Years of Living Dangerously,” that premiered on Showtime in spring 2014. Dr. Basu’s work is widely cited, and she has served as a referee for many epidemiologic, meteorologic, and environmental health journals, as well as for several grant proposals for the U.S. Environmental Protection Agency.