Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period

Wongta, Anurak; Chawansuntati, Kriangkrai; Pata, Supansa; Khamduang, Woottichai; Yodkeeree, Supachai; Hongsibsong, Surat

doi:10.3390/jcm15103791

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Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period

by

Anurak Wongta

^1,2,3

,

Kriangkrai Chawansuntati

²,

Supansa Pata

⁴

,

Woottichai Khamduang

⁴

,

Supachai Yodkeeree

⁵

and

Surat Hongsibsong

^1,2,3,*

¹

School of Health Science Research, Research Institute for Health Sciences, Chiang Mai University, Chiang Mai 50200, Thailand

²

Research Institute for Health Sciences, Chiang Mai University, Chiang Mai 50200, Thailand

³

Environmental, Occupational, and NCD Center of Excellent, Research Institute for Health Sciences, Chiang Mai University, Chiang Mai 50200, Thailand

⁴

Department of Medical Technology, Faculty of Associate Medical Science, Chiang Mai University, Chiang Mai 50200, Thailand

⁵

Department of Biochemistry, Faculty of Medicine, Chiang Mai University, Chiang Mai 50200, Thailand

^*

Author to whom correspondence should be addressed.

J. Clin. Med. 2026, 15(10), 3791; https://doi.org/10.3390/jcm15103791

Submission received: 30 March 2026 / Revised: 6 May 2026 / Accepted: 13 May 2026 / Published: 14 May 2026

(This article belongs to the Section Respiratory Medicine)

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Abstract

Background: Seasonal haze from biomass burning in northern Thailand frequently elevates PM2.5 above national and WHO standards, while evidence on short-term lung function changes in exposed populations remains limited. Method: This longitudinal study evaluated changes in lung function in 130 adults before and after the haze season from December 2023 to May 2024 in San Pa Thong District, Chiang Mai Province. Spirometry was conducted following ATS/ERS standards. Demographic and health-risk data were gathered using validated Thai questionnaires addressing diabetes, cardiovascular, and chronic obstructive pulmonary disease risk categories. Results: A significant reduction in the FEV₁/FVC ratio was observed, from 85.3% to 82.4% (p = 0.001) after the haze period, while the proportion of participants with FEV₁/FVC < 70% increased from 2.3% to 6.9% (p = 0.031). No statistically significant independent predictors were identified in multivariable analysis. Greater reductions were observed in older adults, low-income individuals, and those at moderate to high diabetes risk. Conclusions: These findings suggest modest changes in spirometry parameters during the seasonal haze period. The observed reduction in FEV₁/FVC should be interpreted cautiously and may reflect early functional variation rather than confirmed airway obstruction. Although the magnitude of change was relatively small, the findings highlight the potential value of ongoing respiratory monitoring and early detection strategies in haze-affected regions.

Keywords: PM2.5; seasonal haze; spirometry; lung function; FEV1/FVC ratio; early functional changes; longitudinal study; Thailand

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MDPI and ACS Style

Wongta, A.; Chawansuntati, K.; Pata, S.; Khamduang, W.; Yodkeeree, S.; Hongsibsong, S. Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period. J. Clin. Med. 2026, 15, 3791. https://doi.org/10.3390/jcm15103791

AMA Style

Wongta A, Chawansuntati K, Pata S, Khamduang W, Yodkeeree S, Hongsibsong S. Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period. Journal of Clinical Medicine. 2026; 15(10):3791. https://doi.org/10.3390/jcm15103791

Chicago/Turabian Style

Wongta, Anurak, Kriangkrai Chawansuntati, Supansa Pata, Woottichai Khamduang, Supachai Yodkeeree, and Surat Hongsibsong. 2026. "Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period" Journal of Clinical Medicine 15, no. 10: 3791. https://doi.org/10.3390/jcm15103791

APA Style

Wongta, A., Chawansuntati, K., Pata, S., Khamduang, W., Yodkeeree, S., & Hongsibsong, S. (2026). Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period. Journal of Clinical Medicine, 15(10), 3791. https://doi.org/10.3390/jcm15103791

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Seasonal Decline in Lung Function Among Residents of Northern Thailand: A Longitudinal Study Before and After the Haze Period

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