The aim of this study was to investigate the interaction between cardiovascular disease severity and OA co-morbidity on physical health.
A baseline questionnaire was mailed to 9676 patients aged ≥40 years from UK family practices. A priori exclusive morbidity groups were constructed as follows, based on records 3 years before baseline: (i) reference group--neither cardiovascular disease nor OA; (ii) cardiovascular disease severity index groups--with hypertension, ischaemic heart disease or heart failure without OA; (iii) OA index group without cardiovascular disease and (iv) co-morbid severity groups with hypertension, ischaemic heart disease or heart failure with OA. Adjusted associations between morbidity groups and physical health [mean physical component summary (PCS) score based on the 12-item Short Form Health Survey (SF-12)] compared with the reference group were assessed using linear regression methods.
A total of 5426 patients responded to the baseline questionnaire (56% response). The adjusted mean difference in PCS score between the reference group and the cardiovascular disease index were -2.4 (95% CI -3.4, -1.4) for hypertension, -5.3 (-6.3, -4.3) for ischaemic heart disease and -11.8 (-13.6, -9.9) for heart failure. The difference in the score for the index OA group was -5.6 (-6.5, -4.6). Estimates for co-morbid OA groups were -6.8 (-7.9, -5.7) for hypertension, -9.1 (-10.6, -7.6) for ischaemic heart disease and -12.8 (-16.0, -9.7) for heart failure.
In cardiovascular populations with differing severity, the co-morbid addition of OA was associated with incrementally poorer physical health, but such interactions were less than additive.