Background People spend 90% of their time indoors, yet the health impacts of indoor environmental quality (IEQ) are less understood than outdoor exposures. Understanding how indoor environmental exposures affect health is essential for healthier indoor environments. Objectives To systematically synthesize epidemiological evidence on IEQ exposures and adult health outcomes in high-income country (HIC) indoor settings. Methods Following PRISMA and Synthesis Without Meta-analysis (SWiM) guidelines, PubMed and Scopus were searched (March–April 2024; 7158 records). Eligible studies investigated IEQ exposures and adult health outcomes in HIC indoor settings. Reviewers systematically screened records, extracted data, and assessed risk of bias. Results Data from 74 studies across residential, occupational, educational, and indoor transport environments were synthesized across direct exposures (Category A), source determinants (B), and contextual modifiers (C). Under Category A, PMs, NO 2 , and ultrafine particles linked to reduced lung function and airway obstruction (OR up to 8.16). Indoor cold (<18 °C) associated with objective electrocardiogram (ECG) abnormalities (OR 1.79), radon (>100 Bq/m 3 ) with clinical stroke (OR 1.87), and artificial light at night (as low as 1 lx) with sleep fragmentation and metabolic disruption. For Category B, structural dampness and mould odors consistently elevated adult asthma risks (RR 1.49–1.88). For Category C, open-plan layouts compounded Sick Building Syndrome (SBS) symptoms, whereas “green” certified designs dropped PM 2.5 by 57% and SBS burden by 47%. Furthermore, targeted interventions showed physiological benefits: dynamic lighting mitigated circadian disruptions, while HEPA filtration and indoor greenery mitigated cardiovascular risks. Most studies provided quantified effect estimates with low-to-moderate risk of bias; however, study designs were mainly cross-sectional. Conclusions Poor IEQ adversely affects various health outcomes, most consistently respiratory health and SBS symptoms. These findings underscore the need for longitudinal study designs, evidence-based IEQ guidelines, and better integration of exposure-response data into health impact assessment of indoor environments to support health-promoting building design and management.
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Opbroek et al. (2026) studied this question.