Maryland: Hay fever, or seasonal allergic rhinitis, affects 17.6 million adults in the United States and results in $11.2 billion in related medical expenses. A new multi-institutional study led by researchers from the University of Maryland's School of Public Health and College of Computer, Mathematical and Natural Sciences shows that exposure to more frequent “extreme heat events” increases the prevalence of hay fever among US adults.
“It is well established that extreme heat events are on the rise, and
this trend is projected to continue in response to changing climate,”
explained Amir Sapkota,PhD,
associate professor in the School of Public Health’s Maryland Institute
for Applied Environmental Health and senior author of the study
published in the Journal of Allergy and Clinical Immunology in Practice.
“Our study is the first to provide evidence of how such increases in
extreme heat events contribute to allergic diseases such as hay fever at
a national level.”
The study, “Exposure
to extreme heat events is associated with increased hay fever
prevalence among nationally representative sample of US adults:
1997-2013,” linked National Health Interview Survey Data (1997-2013)
with extreme heat event data. The research team, which included five
UMD researchers as well as scientists from the Centers for Disease
Control and Johns Hopkins University, identified extreme heat events
during 1997-2013 at the county level by comparing the daily maximum
temperature (Tmax) to the county and calendar month specific thresholds
(95th percentile of Tmax values) that were calculated based on 30 years
of baseline data (1960-1989).
The research team used statistical analysis to investigate the
association between increased frequency of extreme heat events and hay
fever prevalence, taking into account other factors such as age,
race/ethnicity, sex, educational level, poverty status, and urban/rural
residence. They found that adults in the highest quartile of exposure to
extreme heat events had a seven percent increase in hay fever compared
to those in the lowest quartile of exposure.
“While the exact mechanisms by which long-term exposures to extreme
heat events increase the risk of hay fever remain unclear, one potential
explanation is changes in plant phenology,” said Crystal R. Upperman,
PhD, lead author of the study. “Higher frequency of extreme heat
events, particularly in the winter and spring may lead to a longer
pollen season as warmer temperatures contribute to earlier onset of
greening and flowering of plants -- including trees-- which are major
sources of pollen.”
Researchers found the timing of extreme heat events also made a
difference in hay fever rates. The association between exposure to
extreme heat events and hay fever was more pronounced for extreme heat
events that occurred during the spring season, with evidence of a clear
exposure-response relationship. This was not the case for extreme heat
events that occurred during the fall season.
Sapkota and Upperman say the seven percent increase in prevalence of
hay fever is modest, but they argue it could have significant
implications for millions of people in the United States who suffer from
allergy, including decreased quality of life and additional medical
According to Raghu Murtugudde,
a leading UMD Earth system scientist and study co-author, U.S. chronic
disease burdens like asthma and other respiratory diseases can cost tens
of billions per year in terms costs of treatment and of lost labor.
"Climate change and atmospheric emissions directly play into changes in
vegetation and pollen combining with heat and pollution to exacerbate
these morbidities. Thus this [study] is another cautionary tale on the
need to factor in such impacts on health as we evolve new emission and
climate policies for the country," Murtuggude said. Read Murtugudde's
LiveScience climate op-eds here.
The study was funded by National Institute of Environmental Health
Sciences (NIEHS) grant 1R21ES021422-01A1 to researchers Chengsheng Jiang
(UMD SPH), Frank C. Curriero (JHU), and Amir Sapkota (UMD SPH).
Publication was also made possible by U.S. Environmental Protection
Agency (EPA) Science To Achieve Results (STAR) grant (F13B20312) to
Crystal Romeo Upperman (UMD SPH).