Synergetic effects of cigarette smoking, systolic blood pressure, and psychosocial risk factors for lung cancer, cardiac infarct and apoplexy cerebri.

With 1,353 inhabitants of a Yugoslavian town, a prospective investigation was carried out during the years 1965-1975. At the beginning, physical and psychosocial risk factors for cancer and other internal diseases were determined; during the next 10 years the incidence of these diseases was recorded. The strongest physical and psychosocial risk factors for lung cancer, cardiac infarct, and apoplexia cerebri were investigated with respect to 'synergetic' effects (interaction nonlinearities), i.e., a dependence of the effect of one variable upon the value of another. They were always present, and the efficacy of physical risk factors was always wholly dependent upon the presence of psychosocial risk factors, while the latter were sometimes quite effective even in the absence of physical ones.