Unsaturated fat intakes and mental health outcomes in young women from the Australian Longitudinal Study on Women's Health

Objective: To determine if associations exist between a range of unsaturated fatty acid intakes and mental health outcomes. Design: Cross-sectional data analysis of the Australian Longitudinal Study on Women’s Health (ALSWH) Young Cohort Survey 3 that included the validated 74 item Dietary Questionnaire for Epidemiological Studies FFQ, validated mental health scales and self-report questions on depression and anxiety.  Setting: Australia, 2003. Subjects: A nationally representative sample of young Australian women (25 to 30 years) from ALSWH. The 7635 women with plausible energy intakes were included in the analyses. Results: Adjusted logistic regression analyses found statistically significant associations between higher intakes of alpha linolenic acid and decreased likelihood of depressive symptoms indicated by the ten item Center for Epidemiological Studies Depression Scale and the Short Form Health Survey mental health subscale. Furthermore, higher intakes of n 6 fatty acids and linoleic acid were associated with decreased likelihood of self reported diagnosed anxiety and higher intakes of n 9 fatty acids and oleic acid were associated with increased likelihood of self reported diagnosed anxiety. Conclusions: Increased intakes of alpha linolenic acid were associated with a reduced likelihood of depressive symptoms, increased intakes of n 6 fatty acids and linoleic acid were associated with a reduced likelihood of self reported anxiety, and increased intakes of n 9 fatty acids and oleic acid were associated with an increased likelihood of anxiety. Additional studies are needed to further elucidate associations between unsaturated fatty acids and depression and anxiety. (Authors abstract)

In recent years there has been an increase in the incidence of mental illnesses, with depression now being the leading cause of disability worldwide. According to the 2007 National Survey of Mental Health and Wellbeing, approximately 45 per cent  of the Australian population have experienced a mental illness in their lifetime and the incidence is increasing by approximately 20 000 cases per annum.  Women, in particular young women, were found to be more likely to experience anxiety and depression, the most common forms of mental illness.  The rise in mental illnesses has correlated with changes in dietary intake in Western countries, in particular a decreased consumption of n 3 fatty acids (FA) and concomitant increases in intakes of n 6 and most likely n 9 FA. The majority of the literature to date focuses on the association between n 3 FA and mental health, in particular depression; however, there are a few studies investigating
N 6 and n 9 FA in relation to mental health. Overall, the association between LC n 3 FA and depression is still unclear. In addition, despite being metabolically plausible, few studies exist that investigate a range of different FA in relation to depression and anxiety. The present study aimed to assess whether a range of dietary unsaturated FA are associated with mental health status a cross-sectional analysis of data from the Australian Longitudinal Study on Women’s Health (ALSWH) Young Cohort Survey 3. The findings demonstrated that women with higher consumptions of ALA were less likely to have depressive symptoms. A study in 853 healthy adults from the province of Attica found that increases in plasma total PUFA, total MUFA, total n 3 FA, DHA, EPA, LA and ALA were all associated with lower scores on Zung’s Self rating Depression Scale. The analyses showed no significant relationship between ALA intake and self reported diagnosed depression. This is possibly due to the wording in the ALSWH survey, which asked women to report if they had been ‘treated or diagnosed’ for depression in the ‘last 3 years’. This is a much longer timeframe than for the FFQ, and therefore the outcome has really been measured before the exposure, and it may be expected that anyone diagnosed and undertaking treatment for depression would not currently be experiencing depressive symptoms. Contrary to much of the existing literature which shows an inverse association between LC n 3 FA and/or fish intake, there were no significant associations found between the LC n 3 FA and the mental health outcomes in the present analyses.

The results also showed that women with higher consumptions of total n 6 FA or LA were less likely to have self-reported anxiety. The agreement between these two explanatory variables is not surprising as for the present analysis LA comprised approximately 98 per cent  of total n 6 intake. The strengths of the present study are the large population-based sample, the ability to control for multiple confounding variables, and the inclusion of validated dietary intake and depression screening tools in the analysis.  The findings of the present study were unexpected as no associations were revealed between the LC n 3 FA and anxiety or depression. While most of the recent research has been conducted in this area, the present findings suggest that further studies are needed of all dietary unsaturated FA as they may be associated with these common and debilitating mental health issues.  Overall, there is limited knowledge about the preventive potential of each type, source, dose or combination of unsaturated FA and the mental health outcomes of depression and anxiety due to a limited literature. Further well designed, large cohort studies are needed that use comparable measures of mental health and validated tools to measure unsaturated FA to ensure consistency in results.  This in turn will strengthen the current evidence base to be able to confidently confirm or refute an association. The current study demonstrated that among a nationally representative sample of young Australian women, an increased intake of ALA but not other n 3 FA was associated with a decreased likelihood of experiencing depressive symptoms. Furthermore, increased intakes of n 6 FA and LA and decreased intakes of n 9 FA and OA were associated with a decreased likelihood of having self-reported diagnosed anxiety. (Editors comments)