A higher degree of insight impairment in stabilized schizophrenia patients is associated with reduced cardiac vagal tone as indexed by resting-state high-frequency heart rate variability.

Varying degrees of impaired clinical insight in schizophrenia differentially impact medication adherence and clinical outcomes, prompting in-depth investigations of the deficits. Research is scarce on the differences in peripheral physiological markers between varying degrees of impaired insight. The aims of this study were to examine the differences in (1) resting-state high-frequency heart rate variability (HF-HRV) and (2) crucial clinical outcomes between schizophrenia patients with varying degrees of insight impairment as measured by the Positive and Negative Syndrome Scale (PANSS) item G12 (lack of judgment and insight). The study recruited a sample of 95 stabilized schizophrenia patients with insight impairment. Patients were divided into 2 groups of either minimal insight impairment (n = 25, PANSS G12 = 2-3) or moderate-to-severe insight impairment (n = 70, PANSS G12 ≥ 4). Patients with moderate-to-severe insight impairment displayed lower HF-HRV, clinician-rated psychosocial function, medication adherence, and working memory capacity, and higher self-reported psychosocial function and life quality, but comparable cognitive insight compared to those with minimal insight impairment. A logistic regression model predicted moderate-to-severe insight impairment based on HF-HRV values at the optimal cut-off point of 3.655, with the sensitivity and specificity 84% and 72%, respectively. HF-HRV seems a peripheral marker sensitively reflecting central pathophysiology implicated in insight impairment of schizophrenia.