Is there an Association between Blood Nutrient Levels and Depression? A Systematic Review

Abstract

This review presents a summary of the available evidence on the relationship between blood nutrient levels and depression. Sixty relevant articles were identified from database searches of studies published from 1994 to 2013. Studies reviewed demonstrated fair support for an association between blood levels of vitamin D and iron with depression, and limited support for an association between blood levels of omega-3 polyunsaturated fatty acids and zinc with depression. Conflicting results were found for other nutrients of interest such as folate, vitamin B12, magnesium and antioxidants. Five prospective cohort studies reviewed here have demonstrated that for some nutrients (vitamin D, iron, folate, omega-3 fatty acids) low blood nutrient levels precede the development of depression. There is insufficient evidence to establish a causal relationship, and it appears likely that that the relationship between blood nutrient levels and depression is bi-directional. There is also limited evidence to demonstrate that low blood nutrient levels are related to dietary intake. Further research is needed to elucidate whether the associations between blood nutrient levels and depression are related to dietary intake. Randomised controlled trials investigating both nutrient supplementation and specific dietary patterns are needed to provide evidence to support dietary recommendations for the prevention and management of depressive disorders.