Few studies have examined the concurrent effects of physical disease and systemic inflammation on suicide risk in patients with depression. The authors investigated the independent contributions of chronic physical disease and systemic inflammation as indexed by C-reactive protein (CRP), on risk of suicide attempt.

In this case–control study, 1468 cases of suicide attempters and 14 373 controls, both aged 18–65 years with a diagnosis of depression during 2011–2015, were identified from the hospital-wide database. Regression models were implemented to identify separate effects of physical diseases and systemic inflammation indexed by CRP, on risk of suicide attempt.

Compared with having no physical disease, having one, two, and three or more physical diseases was associated with a 3.6-, 6.4-, and 14.9-fold increase in odds of making a suicide attempt, respectively, after adjusting for age, sex, and race/ethnicity. In a sub-sample of cases and controls with available CRP values, patients with high CRP (>3 mg/L) had 1.9 times the odds of suicide attempt compared with patients with low CRP (<1 mg/L). This association was no longer significant when controlling for the effect of physical disease.

The presence of physical disease is an important risk factor for suicide attempt among patients with depression. Systemic inflammation is likewise associated with increased risk for suicide attempt, however, this association appears to be accounted for by the presence of physical disease among patients receiving care in a medical center setting. Healthcare providers should consider the risk of suicide attempt in depressed patients burdened with multiple comorbidities.