Triglyceride-glucose index and its association with depressive symptoms in older adults: a longitudinal analysis

The triglyceride-glucose index (TyG) has been proposed as a promising and clinically relevant biological marker of insulin resistance, which is thought to be prevalent among individuals at risk for depression. To date, there have been no longitudinal studies investigating the relationship between an elevated triglyceride-glucose index and subsequent depressive symptoms.

Health measures of 19,114 community-dwelling adults living in Australia and the United States of America, with a mean age of 75 years, were followed up for up to 11 years. Fasting triglyceride levels and fasting glucose levels were used to calculate the triglyceride-glucose index (TyG - the logarithmised product of fasting triglyceride level and fasting glucose divided by two), a marker of insulin resistance and risk for atherosclerotic cardiovascular disease. Depressive symptoms were measured using the Center for Epidemiologic Studies Depression 10-item scale (CES-D-10), with a score ≥ 8 used to indicate a diagnosis of depression. The association between TyG and depression one year later was assessed using generalized estimating equations (GEE), with robust variance estimation to handle repeated measures clustered data. The main model was adjusted for age, gender, ethnicity, living arrangements, education, smoking status, alcohol consumption, body mass index, hypertension, type 2 diabetes, chronic kidney disease, a history of cancer, modified mini-mental state examination score, aspirin use, antidepressant use, diabetic medication use, and lipid-lowering medication use. In a secondary analysis, a Cox proportional hazards model was used to compare the incidence of depression up to 11 years between individuals with the highest baseline TyG group and the lowest baseline TyG.

After adjustments for confounders, the GEE analysis showed no significant relationship between the highest quartile of TyG (compared to the lowest quartile of TyG) and depression one year later. The Cox proportional hazards model showed no significant difference between the highest and lowest TyG and depressive symptoms, when adjusted for the above covariates.

An elevated triglyceride-glucose index was not associated with the later development of depression in fully adjusted models.