Elevated allostatic load—a composite measure of cumulative physiological stress spanning cardiovascular, metabolic, and inflammatory markers—dramatically increased risk for multiple autoimmune conditions in this massive UK Biobank analysis. The highest stress burden quartile showed 5.16-fold higher type 1 diabetes risk, 2.50-fold higher spondyloarthritis risk, and significant increases across seven other immune-mediated inflammatory diseases compared to the lowest quartile. Crucially, high allostatic load also predicted substantially worse survival outcomes, with 6.59-fold higher mortality risk in rheumatoid arthritis patients. This represents a paradigm shift toward understanding autoimmune disease through a stress-physiology lens rather than purely genetic or environmental factors. The finding that physical activity and omega-3 fatty acids partially mitigated these risks offers actionable intervention pathways, while genetic susceptibility scores amplified the stress effects for certain conditions. This comprehensive evidence linking measurable biological stress accumulation to both autoimmune disease onset and progression could revolutionize prevention strategies. Rather than waiting for disease symptoms, clinicians might identify high-risk individuals through allostatic load assessment and implement targeted lifestyle interventions before irreversible autoimmune processes begin.