Fish consumption, blood levels of omega-3 fatty acids, and postnatal depression: a relationship?

Abstract

Evidence suggests that omega-3 (n-3) polyunsaturated fatty acids have a role to play in the aetiology and maintenance of depressive disorders. Studies have reported that countries with high rates of fish oil consumption have low rates of both major depressive disorder and postnatal depression (PND). A lower level of n-3 fatty acids in blood analyses has also been shown to be associated with depression, and in a small number of trials, docosahexanoic acid (DHA) and eicosapentaenoic acid (EPA) have both been seen to be effective treatments for major depression. Research has shown that mothers who have recently given birth are depleted in these n-3 fatty acids, due to the transfer of these acids to the growing fetus. The aim of this study was to test the hypothesis that blood levels of n-3 fatty acids are associated with the occurrence of PND, and further, that those blood levels of n-3 fatty acids are related to diet (specifically intake of oily fish containing n-3) during pregnancy. It was also expected, then, that fish intake during pregnancy would be predictive of PND. Two hundred and forty four women who had given birth within the previous six months were screened for depressive symptoms using the Beck Depression Inventory and the Edinburgh Postnatal Depression Scale. All women scoring above the cut-points on these instruments were interviewed, and postnatal depression was confirmed (or otherwise) using the depression module of the Composite International Diagnostic Interview (CIDI). Forty-one women were interviewed and 21 met the CIDI criteria for an episode of major depression with postpartum onset. A further 39 women who received low scores on the screening measures were included as a control group. All 80 women had blood taken and analysed to determine individual levels of n-3 fatty acids. Data concerning fish consumption during pregnancy, n-3 fatty acids and postnatal depression were analysed using linear and logistic regression procedures. Data were adjusted for household income, which was shown to be significantly associated to depression status. Results indicated that none of the n-3 fatty acid measures were associated with depression status. Consistent with this, fish consumption during pregnancy was not associated with PND. However, as expected, fish consumption during pregnancy was predictive of n-3 fatty acid status after birth. It is suggested that the relationship between n-3 fatty acids and PND is more complex than originally hypothesised, and that future research focus on the possibility that low levels of n-3 only play a role in PND when there are other factors associated with depression present as well.