Social and natural environmental factors cause the birth-cohort phenomenon of peptic ulcers by superposition mechanism.

The widely believed <italic>Helicobacter pylori</italic> infection has never explained the birth-cohort phenomenon of peptic ulcers. Although numerous studies have observed that environmental factors are associated with peptic ulcers, their role in the disease has yet to be identified. A new etiological theory proposed that environmental factors cause peptic ulcers via inducing psychological stress. Starting from this etiology, an integration of the mortality rates caused by social and natural environmental factors reproduced a representative fluctuation curve in the birth-cohort phenomenon, where a causal role of environmental factors in peptic ulcers was hidden. The reproduced fluctuation curve revealed that multiple environmental factors caused the birth-cohort phenomenon by <italic>Superposition Mechanism</italic>, and the causal role of each individual environmental factor surfaced if the fluctuation curves in the birth-cohort phenomenon were properly differentiated. A full understanding of the birth-cohort phenomenon highlights the importance of environmental management in improving clinical outcomes, and suggests that the <italic>Superposition Mechanism</italic> is an indispensable methodological concept for life science and medicine. [ABSTRACT FROM AUTHOR]