Honglei Chen, MD, PhD

Dr. Chen is a Professor at the Department of Epidemiology and Biostatistics of Michigan State University. His research focuses on studying environmental causes of neurodegenerative diseases with the ultimate goal of disease prevention and healthy aging.

 

PRIMARY RESEARCH INTERESTS 

• Search for the environmental causes of Parkinson’s disease and neurodegeneration. Genes and environmental factors, alone or in combination, contribute to the pathogenesis of Parkinson's disease. Over the past decade, Dr. Chen’s research has contributed to a better understanding of the role of environmental factors in Parkinson's etiology.
• Understand the complexity of prodromal neurodegeneration and the roles of the environment. Parkinson’s disease and dementia may take decades to develop, and by the time of diagnosis, it is generally too far gone to intervene. Over the past decades, it has become clear that various nonspecific symptoms (e.g., poor olfaction, dream enacting behaviors) may develop years, if not decades, before the disease’s clinical diagnosis. Dr. Chen studies these prodromal symptoms with two important goals: first to characterize populations at-risk, and second to identify the environmental triggers and modifiers of prodromal neurodegeneration, both critical for disease prevention.  
• Study poor olfaction as “miner’s canary” foretelling deteriorating health in older adults. Besides Parkinson’s disease and dementia, poor olfaction in older adults has been robustly linked to higher mortality. When examining how much of this could be explained by neurodegenerative diseases, Dr. Chen’s team found only ~22%. This suggests most of the health consequences of poor olfaction in older adults remain unknown. Given the high prevalence of poor olfaction in older adults, Dr. Chen is interested in assessing the potential profound health implications of poor olfaction in older adults.

Importantly, these research interests are interconnected and may synergistically improve our understanding of major health issues in older adults and identify preventive strategies. The olfactory system is uniquely positioned at a host-environment interface, and olfaction may thus be a sensitive “sentry” reflecting both intrinsic physiological aging and cumulative damages from environmental insults. Therefore, a comprehensive research program involving environmental risk factors, poor olfaction, and neurodegeneration may significantly advance our understanding of the environmental causes of neurodegenerative diseases in the context of aging.

 

MAJOR RESEARCH PROJECTS

• Airborne pollutants as triggers of Parkinson's Disease via the olfactory system - This is a multi-PI project supported by the US Department of Defense (9/2017-8/2022), supplemented by funding from the Parkinson Foundation. In this project, we have objectively assessed the sense of smell of ~3,400 women, ages 50-79, from the NIEHS Sister Study. The primary goal of this project is to assess the roles of air pollutants in olfactory impairment and their relevance to Parkinson’s disease.
• Pesticides, olfaction, and neurodegeneration among US farmers - This project was initially funded by NIEHS (2/2019 – 1/2024) and is currently supported by NIA (3/2025 – 1/2030). In the NIEHS-supported R01, we enrolled a sub-cohort of ~2,500 farmers from the Agricultural Health Study to investigate the roles of pesticides in olfactory impairment and their relevance to prodromal neurodegeneration. In the newly NIA-funded R01, we will prospectively follow these farmers with repeated assessments of olfaction, gustation, cognition, and other prodromal symptoms of Alzheimer’s disease and related neurodegeneration. We will also collect blood samples from ~800 farmers to measure plasma-based biomarkers of Alzheimer's disease. These will empower us to examine potential associations of pesticides and other farming exposures in relation to markers of Alzheimer’s disease and related neurodegeneration across the continuum of neurodegeneration in a unique farming population. 
• Poor olfaction and the health of older adults - In this R01 project (6/2022 – 2/2027), we aim to answer two novel and clinically-significant questions: 1) What adverse health outcomes can a poor sense of smell in older adults potentially herald, in addition to neurodegenerative diseases? 2) Is poor olfaction a marker of accelerated aging? We will conduct secondary data analyses in the Health ABC and ARIC studies.

These projects support the team’s research interests and approach. With these valuable and complementary resources from well-established longitudinal cohorts, Dr. Chen aims to decipher the codes of poorly understood poor olfaction, prodromal neurodegeneration, environmental causes, and beyond.

 

BIOGRAPHY

Dr. Chen earned his M.D. (equivalent) from TianJin Medical University in TianJin, China, and Master's degree from the Chinese Academy of Preventive Medicine in Beijing, China. In 2001, he earned his Ph.D. in Nutritional Epidemiology from Tufts University in Boston, MA, and then worked as a Research Fellow and Instructor at the Harvard School of Public Health. From 2005-2016, Dr. Chen worked at the Epidemiology Branch of the National Institute of Environmental Health Sciences and received his Tenured Senior Investigator appointment from NIH in 2013. Dr. Chen joined Michigan State University in 2016 as a professor in the Department of Epidemiology and Biostatistics, and was recognized with the MSU Foundation Professorship in 2021 for his excellence in research. 

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SELECTED MEDIA COVERAGE:

1. The Michael J. Fox Foundation's research-focused podcast. Examining Links Between Environmental Exposure, Poor Olfaction, and Parkinson's Disease
2. NIEHS Environmental Factor: Sniffing Out Signs of Neurodegeneration
3. Michiagn Public NPR Stateside: : Poor sense of smell in elderly connected to shorter life expectancy
4. YouTube: My sense of smell, who cares!
5. MSU News Release: Poor olfaction and pneumonia risk

 

SELECTED PUBLICATIONS IN RECENT YEARS
 

• Yuan Y*, Plassman BL, Song S*, Luo Z, Parks CG, Hofmann JN, Beane Freeman LE, Sandler DP, Chen H. High pesticide exposure events and subjective cognitive complaints among US farmers. Environ Res. 2026 Jan 7:123731. doi: 10.1016/j.envres.2026.123731. Online ahead of print. PMID: 41512992
• Shrestha S, Zhu X, Kucharska-Newton A, Yuan Y*, Kamath V, Palta P, Deal J, Mosley T, Griswold M, Chen H. Characterizing the olfaction and dementia association in the community-based ARIC Study Alzheimer’s & Dementias 2025 Feb;21(2):e14613. doi: 10.1002/alz.14613.PMID: 39988999 PMCID: PMC11847982
• Ding G*, Xia J*, Pinto JM, Esber Z, Yuan Y*, Li C, Tian Q, Kucharska-Newton A, Simonsick EM, Chen H. Poor olfaction is associated with lower pulmonary function in older adults. Chest. 2025 Sep 20:S0012-3692(25)05265-1. doi: 10.1016/j.chest.2025.08.041. PMID: 40983166; PMCID: PMC12507451
• Song S*, Luo Z, Plassman BL, Huang XM, Yuan Y*, Shrestha S, Parks CG, Hoffmann JN, Beane-Freeman LE, Sandler DP, Chen H: Self-reported motor and nonmotor symptoms, prodromal PD probability, and incident Parkinson’s disease in U.S. Farmers Movement Disorders 2025 Feb 14. doi: 10.1002/mds.30149. PMID: 39950732
• Chamberlin KW*, Li C, Kucharska-Newton A, Luo Z, Reeves M, Shrestha S, Pinto JM, Deal J, Kamath V, Couper D, Palta P, Mosley T, Chen H. Poor olfaction and risk of stroke in older adults: The Atherosclerosis Risk in Communities Study. Stroke. 2025 Feb;56(2):465-474. doi: 10.1161/STROKEAHA.124.048713. PMID: 39869711  PMCID: PMC11774471
• Yuan Y*, Chamberlin KW*, Li C, Luo Z, Kucharska-Newton A, Simonsick EM, Chen H. Olfaction and Mobility in Older Adults JAMA Otolaryngology-Head & Neck Surgery 2024 Mar 1;150(3):201-208. doi: 10.1001/jamaoto.2023.4375.
• Cao Z*, Yuan Y, White AJ, Li C, Luo Z, D'Aloisio AA, Huang X, Kaufman JD, Sandler DP, Chen H. Air Pollutants and Risk of Parkinson's Disease among Women in the Sister Study. Environ Health Perspect. 2024 Jan;132(1):17001. doi: 10.1289/EHP13009. Epub 2024 Jan 4. PMID: 38175185 PMCID: PMC10766011
• Yuan Y*, Shrestha S, Luo Z, Li C, Plassman BL, Parks CG, Hofmann JN, Beane Freeman LE, Sandler DP, Chen H: High Pesticide Exposure Events and Dream-Enacting Behaviors Among US Farmers Mov Disord. 2022 Feb 13. doi: 10.1002/mds.28960. PMID: 35152487
• Yuan Y*, Luo Z, Li C, Pinto JM, Shiroma EJ, Simonsick EM, Chen H: Poor olfaction and pneumonia hospitalisation among community-dwelling older adults: a cohort study. Lancet Healthy Aging May 21, 2021, 2(5): e275
• Liu B*, Luo Z, Pinto JM, Shiroma EJ, Tranah GJ, Wirdefeldt K, Fang F, Harris TB, Chen H. Relationship Between Poor Olfaction and Mortality Among Community-Dwelling Older Adults: A Cohort Study. Ann Intern Med. 2019 May 21;170(10):673-681. doi: 10.7326/M18-0775. Epub 2019 Apr 30. PubMed PMID: 31035288.

 * Trainees