Purpose: The present study aimed to explore the possible difference in plasma neuropeptide Y (NPY) level between patients with primary insomnia and healthy normal sleepers.
Methods: The sample comprised 42 patients with primary insomnia and 38 age- and sex-matched healthy controls. Clinical measures, including the Pittsburgh Sleep Quality Index (PSQI), State-Trait Anxiety Inventory (STAI), and Beck Depression Inventory (revised edition, BDI-R), were recorded, respectively. Morning fasting plasma NPY levels of all participants were determined by using enzyme-linked immunosorbent assay (ELISA). Student's t-test or chi-square test was used to compare the differences in demographic and clinical factors and scores of psychometric assessments between groups. Bivariate correlation test was used to analyze the relationship between NPY level and factors, such as age, body mass index (BMI), PSQI, STAI, and BDI-R score. Analysis of covariance (ANCOVA) was used to study the difference of plasma NPY level between two groups with adjustment for age, sex, BMI, STAI, and BDI-R total score.
Results: We found that morning plasma NPY levels in patients with primary insomnia were significantly lower than those in the normal controls (5.11 ± 2.87 vs. 7.01 ± 3.44 ng/ml, p = 0.009). The difference in plasma NPY level persisted even after adjustment for age, sex, BMI, STAI, and BDI-R total score (p = 0.026). For all subjects, plasma NPY level was found decreasing significantly with age (r = -0.232, p = 0.038). In addition, there was a trend that plasma NPY level was negatively associated with PSQI total score (r = -0.209, p = 0.063).
Conclusions: Our findings suggest that NPY system may involve in the pathophysiological process of primary insomnia. Further studies are warranted to determine the causal relationship between low plasma NPY level and primary insomnia disorder.