Linking salt consumption to depression: triangulating evidence from Mendelian randomization and observational studies

Limited research has examined the combined effects of dietary sodium intake on depressive symptoms. The objective of this study was to evaluate the association between frequently adding salt to food and depressive symptoms, as well as the underlying mechanisms.

A total of 15,471 adults from the 2007 to 2018 National Health and Nutrition Examination Survey (NHANES) were included in the study. Depressive symptoms were defined as a total score of ≥10 on the Patient's Health Questionnaire (PHQ-9). Participants self-reported the frequency of adding salt to their foods, categorized as never or rarely, sometimes, usually, or always. Multivariable logistic regression analyses were conducted to evaluate the association between frequently adding salt to food and risk of depression. Bidirectional Mendelian randomization (MR) analysis was employed to investigate the potential causal relationship.

In the multivariate model, a significant positive association was observed between frequently adding salt to food and the risk of depression. After adjusting for covariates, a higher self-reported frequency of adding salt to food was significantly associated with an elevated risk of depression (OR: 1.26; 95% CI: 1.16-1.38; P < 0.001). Furthermore, MR analysis indicated that higher salt intake was causally linked to an 11% increased risk of depressive symptoms and 28% increased risk of major depressive disorder.

Frequently adding salt to food is positively associated with depression. These findings suggest that reducing the frequency of adding salt to foods at the table may be an effective strategy to lower risk of depression in the general population.