High Pollen Exposure Linked to Increased Chronic Respiratory Mortality

According to a recent study, exposure to high pollen concentrations was linked to increased all-cause and chronic respiratory mortality among older adults.1

“We found mixed evidence to suggest lag associations between exposure to common classes of pollen species and respiratory related mortality in a temperate, Midwestern state of the United States,” wrote investigators, led by Peter S. Larson, PhD, from the Social Environment and Health Program, Institute for Social Research, at the University of Michigan. “Risks varied by exposure level and lag exposure days, suggesting that the timing between exposure and death can be as long as two weeks for extreme levels of deciduous broadleaf and as little as one week for ragweed pollens.”

Plant-derived aeroallergen levels are rising due to the elongation of growing seasons and intensifying anthropogenic climate change.2 Increased pollen exposure can be harmful to people, especially older adults, increasing their mortality risk from respiratory causes.

Investigators sought to determine the short-term associates of 4 species classes of pollen—ragweed, deciduous trees (maple, alder, birch, mulberry, sycamore, poplar, oak, elm), grass pollen, and evergreen trees (Cupressaceae and Pinaceae families)—with respiratory mortality in Michigan.1 Pollen data was collected from a prognostic model of daily pollen concentrations at 25 km resolution.

The team examined for all-cause and chronic and infectious-related mortality, obtaining records for all Michigan deaths from 2006 – 2017 from the Michigan Department of Health and Human Services. They selected deaths from infectious and chronic respiratory-related causes using the International Classification of Diseases (ICD-10) codes.

The study included 127,163 deaths from respiratory causes between January 1, 2006, and December 31, 2017, with 51.4% female, 90% White, and 9.42% Black. 61.2% of deaths were due to chronic lower respiratory causes and 19.9% were due to infectious respiratory causes. COPD was linked to 54.9% of respiratory deaths.

The team examined the risk of death at high levels of cumulative exposure (90th percentile) compared with no exposure for lag days 0, 0 – 1, 0 – 7, and 0 – 15. Investigators had attempted to include precipitation, temperature, and air pollution as potential confounders in the analyses’ model, but these variables resulted in unstable parameter estimates due to the fact precipitation and temperature are both used to determine pollen concentrations.

Cumulative daily high concentrations (90th percentile) of deciduous broadleaf, grass, and ragweed were linked to all-cause respiratory mortality. For instance, people exposed to deciduous broadleaf pollen at the 90th percentile had a 1.14 greater risk at 1-day lag exposure for all respiratory deaths (odds ratio [OR], 1.14; 95% confidence interval [CI], 1.02 to 1.27) and a 1.81 greater risk at cumulative 7-day lag exposure (95% CI, 1.04 – 3.15).

Furthermore, exposure to high concentrations of grass and ragweed pollens were associated with an increased risk of death from chronic respiratory causes. At an exposure of 2 weeks, investigators observed a significant protective effect of grass pollens on all respiratory (OR, 0.55; 95% CI, 0.41 to 0.73) and of infectious respiratory mortality (OR, 0.52; 95% CI, 0.28 to 0.98).

“The significant results for grass exposure could reflect differences in exposure to grass pollens through outdoor occupations and activities such as lawn maintenance or recreation,” investigators wrote.

1-day lag exposure of ragweed was significantly associated with all respiratory mortality (OR, 1.31; 95% CI, 1.11 to 1.56) and for chronic respiratory mortality up to 1 week (OR, 2.16; 95% CI, 1.22 to 3.80). The odds of death from COPD were linked to a ragweed exposure of ≥ 1 week (OR, 2.07; 95% CI, 1.14 to 3.77).

Investigators observed no association between any pollen species and death from infectious respiratory causes; however, there was a positive but non-significant association of exposure to deciduous broadleaf and ragweed pollens. Moreover, evergreen pollen was not observed to be linked to any kind of mortality.

“…our study provides new evidence that specific types of pollens may be associated with increased risk for mortality from respiratory causes,” investigators concluded. “With projected increases in pollen levels with climate change, pollen-associated health effects, including mortality, stand to increase, efforts to prevent pollen-associated health effects should be increased, including prompt diagnosis and treatment of pollen allergies, immunotherapy, and enhanced pollen forecasting to adapt to a changing climate.”

References

1. Larson PS, Steiner AL, O'Neill MS, Baptist AP, Gronlund CJ. Chronic and infectious respiratory mortality and short-term exposures to four types of pollen taxa in older adults in Michigan, 2006-2017. BMC Public Health. 2025 Jan 16;25(1):173. doi: 10.1186/s12889-025-21386-3. PMID: 39815234; PMCID: PMC11737261.
2. Anderegg WRL, Abatzoglou JT, Anderegg LDL, Bielory L, Kinney PL, Ziska L. Anthropogenic climate change is worsening North American pollen seasons. Proc Natl Acad Sci U S A. 2021 Feb 16;118(7):e2013284118. doi: 10.1073/pnas.2013284118. PMID: 33558232; PMCID: PMC7896283.