Synergistic interaction of smoking and neuroticism as a risk factor in ischaemic heart disease: case-control study

Contemporary epidemiology and health psychology research has pointed out that single risk factors have relatively little influence on ischaemic heart disease (IHD), but that effects are synergistic. The possibility of such interactions has occasionally been noted and indeed might be expected, given the unexplained variance in IHD risk after accounting for the effects of IHD risk factors taken individually. Risk factors of smoking and neuroticism (emotional lability) were investigated simultaneously in groups of 187 male IHD patients and 187 controls. Initially, a logistic regression was used to compare the two groups on the two risk factors. Next, their interaction was tested by dividing the two samples into different subgroups according to the level of neuroticism and presence of smoking. The multivariate regression model and other methods supported both risk factors including a synergistic interaction between the two. The synergistic interaction of smoking and neuroticism plays an important role in predicting IHD. Different potential mechanisms of psychobehavioural pathogenicity have been suggested so far. The presence of a psychobiological synergistic interaction between neuroticism and smoking suggests the involvement of the former risk factor in sudden deterioration in the coronary flow due to vasoconstriction.