Background/Purpose: Environmental heat exposures have been linked to increased morbidity and mortality. Individuals with systemic lupus erythematous (SLE) often have heat- and photo- sensitivity, which may make them particularly vulnerable to environmental heat exposure. While exposure to heat has been associated with disease flares and hospitalization among individuals with SLE, it is unknown whether exposure to extreme heat is associated with incident SLE and how socioeconomic factors may impact the association.

Methods: We use data from 48,934 eligible participants in the Sister Study, a prospective breast cancer cohort in the US aged 35 to 74 (enrollment: 2003-2009). Eligible participants had no prior history of SLE and had heat exposure data linked to their residential address at enrollment. Incident SLE was self-reported during follow-up through October 2022. PRISM weather data were obtained at 4km resolution and linked to participant baseline residence to estimate single year and 3-year average estimates of average daily maximum apparent temperature (i.e., heat index) and the total number of hot days where the apparent temperature exceeded 85 degrees Fahrenheit (F). Hazard ratios (HR) and 95% confidence intervals (CI) for SLE associated with quartile differences in heat measures were estimated using Cox proportional hazards regression. Models were adjusted for age, enrollment year, race and ethnicity, age at menarche, smoking status, alcohol status, and body mass index. We explored effect measure modification, stratifying by educational attainment—a proxy for resource availability to potentially mitigate heat exposure.

Results: Over follow-up (672,477 person years), 395 participants reported incident SLE after enrollment (mean age at diagnosis: 61±10 years) with an average time to diagnosis of 6.4 years. Increasing quartiles of environmental residential heat were associated with greater SLE. Individuals living in areas of the highest quartile of 3-year average daily apparent temperature had 1.35 (CI:1.00, 1.82) times greater SLE hazard than those living in the lowest quartile. Similarly, SLE hazard was also elevated for individuals living in areas in the highest quartile of 3-year average number of annual days over 85F compared to participants living in the lowest quartile (HR:1.40; CI:1.04, 1.89). Single year associations were similar in magnitude and trend. When stratified by educational attainment, participants who reported less than a bachelor’s degree and lived in areas in the highest quartile of 3-year average annual days over 85F had 1.47(CI:1.00, 2.16) times greater SLE hazard compared to those in the lowest quartile. SLE hazard was slightly lower for participants who attained a bachelor’s degree or higher (HR:1.24; CI:0.78, 1.97) and lived in the hottest areas.

Conclusion: Environmental heat exposure was associated with increased hazard of SLE. Associations were slightly modified by educational attainment, a proxy for potential availability of socioeconomic resources to mitigate heat exposure. Environmental heat exposure should be further assessed as a potential risk factor for SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/environmental-heat-exposure-and-risk-of-systemic-lupus-erythematosus/