Association between muscle quality index and depression in adults: A cross-sectional study

<h2>Abstract</h2><h3>Background & Aims</h3> The muscle quality index (MQI) score is a new indicator of muscle quality and is closely related to physical health. This study aimed to investigate the association between the MQI score and depression in young and middle-aged people. <h3>Methods</h3> Complete MQI and depression data were obtained from the National Health and Nutrition Examination Survey (NHANES) database from 2011-2014 for 5199 subjects aged 20–60 years. An assessment of depression was conducted using the Patient Health Questionnaire (PHQ-9). Appendicular skeletal muscle mass (ASM) and handgrip strength (HGS) were measured via dual-energy X-ray absorptiometry (DXA) and a dynamometer, respectively. MQItotal, MQIapp and MQIarm were calculated by HGS sum/ASM (kg/kg), dominant HGS/ASM (kg/kg), and dominant HGS/dominant arm ASM (kg/kg), respectively. Multivariate regression analyses, subgroup analyses, trend tests, interaction tests, smooth curve fitting, and threshold effect and saturation effect analyses were performed. <h3>Results</h3> The mean age of the included population was 38.76 ± 11.57 years, of which 48.5 1% were female. Multivariate regression analyses revealed that the MQI score was negatively correlated with depression. Subgroup analyses revealed that this association was present in females but not in males. After all included confounders were adjusted, the risk of depression in women decreased by 32 %, 35 %, and 6 %, as MQItotal (OR 0.68, 95% CI 0.54–0.84), MQIapp (OR 0.65, 95% CI 0.47–0.91) and MQIarm (OR 0.94, 95% CI 0.90–0.99) increased per unit, respectively. Women in MQItotal, MQIapp, and MQIarm quartile 4 had a significantly lower incidence of depression than did those in quartile 1. In addition, smoothing curve fitting revealed that MQItotal, MQIapp, and MQIarm were not linearly correlated with the risk of depression in women but rather had a J-shaped relationship, with inflection points of 2.24, 1.01 and 8.35, respectively. <h3>Conclusions</h3> According to the results of this study, MQI scores negatively correlate with depression in women, but not in men, demonstrating a J-shaped relationship.