A new investigation published in the journal Translational Psychiatry has suggested that moderate fish consumption could reduce the risk for the major depressive disorder (MDD) at least in older individuals living in an area known for high fish intake.

A cohort study of almost 1200 older adults in Japan showed that those who were in the third quartile for fish intake (111.1 g/d) had a significantly lower risk for MDD than those in the lowest quartile (57.2 g/d).

However, there was no significant association with depression risk for the participants in the fourth highest quartile of fish intake (152.6 g/d; OR, 0.75), suggesting that there was a reverse J-shaped effect, said lead author Dr Yutaka J. Matsuoka.

A systematic review of observational studies has revealed that fish consumption and levels of n-3 polyunsaturated fatty acids (PUFAs) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid are associated with a reduced risk of depression.

However, there is limited evidence from populations with high fish consumption and no studies have used a standard psychiatrist-based diagnosis of MDD. Information collected from the new study would be useful for the prevention of MDD in a fish-eating population.

The current analysis assessed 1181 participants (mean age, 73 years) in the Japan Public Health Center-based Prospective Study. The individuals completed two food frequency questionnaires and underwent a mental health examination.

Daily fish consumption for each participant, in grams per day, was determined by multiplying standard portion size by frequency. The fatty acid composition table of Japanese foods was used to calculate the daily intake of n-3 PUFAs and n-3 PUFA subtypes.

Among the full cohort, 95 participants received a diagnosis of MDD during follow-up of up to 25 years. Moderate intake of fish, EPA, and DPA were associated with significantly reduced risk for MDD compared with each dietary type's lowest quartiles.

Emerging and compelling evidence suggests that diet and nutrition are extremely important factors in the high prevalence of depressive disorders, and the findings provide a basis to further examine the effectiveness of fish and n-3 PUFA intake for the prevention of MDD in aged individuals.

The study's strengths included the large sample size and that they did have very solid findings that for at least one of the quartiles of fish and DPA intake, there is certainly a statistically significant reduction in the risk of depression.

However, although there were trends for the highest level of fish consumption not being optimal, none of the results in this highest level was significantly different from the second and third quartiles.

The team pointed out that trying to divide 95 people with depression into four quartiles could lead to small group numbers. We will become underpowered and vulnerable to confounders.

The takeaway message is that this is consistent with a large body of other data studied finding a protective association between fish consumption and lower risk of depression.