There has been increasing attention given to the relationship between lifestyle and risk of depression, with diet being one aspect of interest. A recent study found that a Mediterranean-style diet (high in fruits, vegetables, fish and whole grains) is associated with a decreased risk of depression (Lai et al. 2014). However, it is not clear which, if any, is the key ingredient in this health mix.
Fish are known to be an important source of n-3 polyunsaturated fatty acids, often known as fish oils, which play a role in brain structure and function. There have been a number of studies reporting an association between fish consumption and depressive risk, though there have also been contradictory findings.
The authors of the present paper (Li et al. 2015) therefore sought to find all studies on the subject and conduct a meta-analysis to determine the overall findings.
The authors searched PubMed, EMBASE and Web of Science for studies that evaluated the relationship between fish consumption and the risk of depression.
They identified 26 studies, of which 10 were cohort studies and 16 were cross-sectional studies. In total, these studies involved 150 278 participants who were from the general population (studies involving diseased populations were excluded).
Depression was defined in the studies either by diagnosis by a doctor, based on beginning regular use of an antidepressant medication or identified by interview or depression rating scales.
The authors calculated the relative risks of depression for the groups with the highest versus the lowest consumption of fish.
They also conducted a meta-regression to try to identify sources of heterogeneity between the studies and they evaluated publication bias by Egger’s test and using a funnel plot.
Among the 26 studies, 12 showed a significant association between fish consumption and depression, while the other 14 demonstrated no relationship between them.
The pooled relative risk (RR) of depression for the group with the highest level of fish consumption was 0.83 (95% CI 0.74 to 0.93) compared to the group with the lowest level of fish consumption.
This matched the findings in the 10 cohort studies identified, which found a RR of 0.84 (95% CI 0.75 to 0.94) and the 16 cross-sectional studies (RR = 0.82, 95% CI 0.68 to 1.00).
Results were similar for men (RR = 0.80) and women (RR = 0.84).
The results were significant for studies conducted in Europe (RR=0.72, 95% CI 0.63 to 0.82), but not for those conducted in other continents.
Moderate to high heterogeneity was observed in the analysis (I2=64.5%, PQ<0.001).
However, meta-regression analysis demonstrated that none of the following characteristics contributed significantly to between-study heterogeneity: continent; sex; study design; sample size; publication year; incidence of depression; quality of study; dietary intake assessment and depression diagnosis method.
The authors also found no evidence of publication bias on both the funnel plot and Egger’s test.
This meta-analysis provides evidence for a relationship between higher levels of fish consumption and lower levels of depression risk. The study found that those participants who consumed the greatest amount of fish had a 17% decreased risk of depression compared to those who consumed the least amount of fish. These results were similar for men and women, and were significant in studies conducted in Europe but not those from other continents.
The large number of participants captured in this meta-analysis gives strength to the analysis.
The finding that a relationship between fish consumption and depressive risk was evidence in cohort studies, and not only cross-sectional studies indicates a potential causal relationship.
No publication bias was detected by the analysis.
Fish consumption was measured by widely differing means, making it difficult to compare across studies. As dosages could not be directly compared the authors calculated the difference in depression incidence within each study between highest and lowest consumers of fish.
The method of measuring depression was also inconsistent between studies, varying from diagnostic interviews with standardised scales to physician-reported diagnoses or based on regular antidepressant use.
Higher fish consumption was found to be associated with a reduced risk of depression. Randomised controlled trials are required to establish whether this relationship is causal and to determine what dose of fish may be beneficial. Questions also remain over what type of fish may be important and whether it is the fish oil component of the fish that may play a beneficial role.
Li, F., Liu, X., & Zhang, D. (2015). Fish consumption and risk of depression: a meta-analysis. Journal of Epidemiology and Community Health, jech-2015. [Abstract]
Lai JS, Hiles S, Bisquera A, et al. A systematic review and meta-analysis of dietary patterns and depression in community-dwelling adults. Am J Clin Nutr 2014;99:181–97.