Key Findings:
The association between n6 and n3 fatty acids and new-onset depression was assessed in this study using a large prospective cohort of women. A lower risk of clinical depression was correlated with ALA intake especially among those who had the lowest intake of LA. ALA deficiency has been linked with altered brain biochemistry, such as membrane structure and fluidity, ion channels, second messengers, reduced cyclic AMP response element-binding protein transcription factor activity and brain-derived neurotrophic factor expression, and increased expression of cytosolic and secretory phospholipase A2 and cyclooxygenase-2. ALA deficiency has been shown in animal research to change serotoninergic and dopaminergic neurotransmission in the frontal cortex.
ABSTRACT:
The associations between different sources of dietary n-3 and n-6 fatty acids and the risk of depression have not been prospectively studied. The objective was to examine the relation between different n-3 and n-6 types with clinical depression incidence. We prospectively studied 54,632 US women from the Nurses’ Health Study who were 50–77 y of age and free from depressive symptoms at baseline. Information on diet was obtained from validated food-frequency questionnaires. Clinical depression was defined as reporting both physician-diagnosed depression and regular antidepressant medication use. During 10 y of follow-up (1996–2006), 2823 incident cases of depression were documented. Intake of long-chain n-3 fatty acids from fish was not associated with depression risk [relative risk (RR) for 0.3 g/d increment: 0.99; 95% CI: 0.88, 1.10], whereas alpha-linolenic acid (ALA) intake was inversely associated with depression risk (multivariate RR for 0.5 g/d increment: 0.82; 95% CI: 0.71, 0.94]). The inverse association between ALA and depression was stronger in women with low linoleic acid (LA) intake (P for interaction = 0.02): a 0.5-g/d increment in ALA was inversely associated with depression in the first, second, and third LA quintiles [RR (95% CI): 0.57 (0.37, 0.87), 0.62 (0.41, 0.93), and 0.68 (0.47, 0.96), respectively] but not in the fourth and fifth quintiles. The results of this large longitudinal study do not support a protective effect of long-chain n-3 from fish on depression risk. Although these data support the hypothesis that higher ALA and lower LA intakes reduce depression risk, this relation warrants further investigation. (Author’s Abstract)