The association between nutrition and depression

Abstract

Depression is one of the most common mental disorders worldwide, affecting more than 300 million people. In Australia, one in five people aged 16-85, experience mental illness, depression being most common. Emerging evidence indicates that diet may influence the onset of depression. This study aimed to: 1) determine the association between dietary patterns and depressive symptoms (DepS) in Australian adults by using three dietary pattern analysis methods i.e. principal component analysis (PCA), reduced-rank-regression (RRR), and partial-least squares (PLS) methods; 2) obtain further insights into the physiological mechanisms by establishing the association between nutrient patterns (NPs) and DepS; 3) determine the link between the energy-adjusted dietary inflammatory index™ (EDII ™) score and the risk of DepS. This thesis utilized data from two stages [Stage 3 and North West 2015 (NW15)] of the North West Adelaide Health Study (NWAHS) cohort. The Centre for Epidemiological Studies-Depression (CES-D) scale and food frequency questionnaire (FFQ) was used to measure DepS and dietary data, respectively. Our findings showed 16.9% of the participants had DepS and females (20.8%) were more depressed than males (14.2%). The ‘prudent’ dietary pattern captured by PCA [ORQuartile4vs1 = 0.57; 95% CI: 0.35, 0.92 ; p = 0.021, ptrend = 0.06], RRR [ORQuartile4vs1 = 0.66; 95% CI: 0.43, 1.00; p = 0.048; ptrend = 0.117] and the ‘typical Australian’ dietary pattern determined by RRR [ORQuartile4vs1 = 0.60; 95% CI: 0.40, 0.90; p = 0.014; ptrend = 0.013] were inversely related with DepS. The ‘western’ dietary pattern captured by PCA [ORQuartile4vs1 = 2.04; 95% CI: 1.13, 3.68; p = 0.017; ptrend = 0.016] and PLS [ORQuartile4vs1 = 1.62; 95% CI: 1.05, 2.50; p = 0.030; ptrend = 0.054] was positively associated with DepS. The ‘plant-sourced’ NP was found to be inversely associated with DepS [ORQuartile4vs1 = 0.76; 95% CI: 0.48–1.20], whereas an ‘animal-sourced’ [ORQuartile4vs1 = 1.00; 95% CI: 0.64–1.56] or ‘mixed-source’ NP [ORQuartile4vs1 = 0.84; 95% CI: 0.47– 1.48] was not associated with DepS. An inverse association were observed between the ‘plant-sourced’ NP and the ‘(absence of) positive-affect’ factor from the CES-D [ORQuartile4vs1 = 0.67; 95% CI: 0.46-1.00; p = 0.048]. A diet with higher E-DIITM score (pro-inflammatory diet) was found to be linked with a 79% increase in odds of reporting DepS [ORQuartile4vs1:1.79; 95% CI: 1.14-2.81; ptrend = 0.026]. Men with a higher DII had a two-fold higher odds ratio of DepS [ORQuartile4vs1:2.27; 95% CI: 1.02-5.06; ptrend = 0.089]. Women with a higher DII had an 81% increase in odds of DepS [ORQuartile4vs1:1.81; 95% CI: 1.01-3.26; ptrend = 0.068]. These associations were also evident in the longitudinal analysis. The meta-analysis (n = 12) showed that a pro-inflammatory diet was associated with a 45% increase in odds of having DepS [ORQuartile4vs1:1.45; 95% CI: 1.20,1.74, p-value < 0.01]. Findings from all three studies have contributed to the epidemiological literature by providing empirical support for the relationships between nutrition and depression. In conclusion, ‘prudent’ and ‘typical Australian’ dietary patterns or ‘plant-sourced’ NPs or ‘anti-inflammatory’ diet may be beneficial strategies to alleviate the risk of DepS.