M Lucas, F Mirzaei, E O’Reilly, A Pan, WC Willett, I Kawachi, K Koenen, A Ascherio Harvard School of Public Health, Boston, United States of America

Objective: To examine the relationship between different types of n-3 and n-6 fatty acids, and the risk of clinical depression.

Procedure: We prospectively studied 73,449 women from the Nurses’ Health Study who were 46 to 79 years of age and free from depressive symptoms at baseline (1996). Information on diet was obtained from validated food frequency questionnaires completed four times before baseline (1984, 1986, 1990, 1994). Clinical depression was defined as reporting both physician-diagnosed depression and regular antidepressant medication use. During 10 years of follow-up (1996-2006), 3,406 incident cases of clinical depression were documented. Cox-proportional hazard models, adjusted for age and other possible risk factors, were used to calculate relative risks (RR) of depression.

Results: Intake of n-3 from seafood was not associated with risk of depression (multivariate RR for 0.3 g/day increment= 0.96 [0.87 to 1.06]; P=0.411). Intake of alpha-linolenic acid was not associated with risk of depression, except in regression models adjusted for n-6 fatty acids (multivariate RR for 0.5 g/day increment = 0.78 [0.69 to 0.89]; P=0.0001). Intake of linoleic acid was associated with a higher risk of depression (multivariate RR for 5 g/day increment = 1.29 [1.11 to 1.49]; P=0.001), whereas arachidonic acid intake was not associated with risk of depression (multivariate RR for 0.1 g/day increment = 1.03 [0.90 to 1.17]; P=0.677).

Conclusions: The results of this large longitudinal study do not support a protective effect of marine n-3 fatty acids or fish intake on risk of depression. However, this study provides support for the hypothesis that a higher alpha-linolenic acid intake and a lower intake linoleic acid might reduce the risk of clinical depression, but this relation deserves further investigation.

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