The anti-depressive effects of omega-3 fatty acids — particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) — in those suffering from depression have been explored in previous studies, but trials assessing their ability to prevent depression or maintain mental health among non-depressed individuals are rare.
Researchers in Japan thus conducted an RCT to determine omega-3's effectiveness on hospital nurses. They randomly assigned 80 junior nurses to each receive either 1,200mg of EPA and 600mg of DHA, or identical placebo pills, daily for 13 weeks.
They used the Hospital Anxiety and Depression Scale (HADS) to measure participants' scores at 13, 26, and 52 weeks from study enrolment, based on incidences of major depressive episodes, depression severity, anxiety, insomnia, burnout, and presenteeism at work.
Subsequently, they observed that the mean HADS baseline score of 7.2 fell to 6.32 in the treatment group and 6.81 in the placebo group at 26 weeks.
However, despite lower insomnia severity at 13 weeks, absolute presenteeism at 26 weeks, and a significantly lower HADS score and depression severity at 52 weeks, the treatment group showed no significant superiority or inferiority when it came to major depressive episodes, anxiety, or burnout.
The researchers also wrote: "The additive value of omega-3 fatty acids was not confirmed regarding mental state and self-evaluated work efficiency."
In terms of limitations, they had recruited fewer subjects than initially intended as not enough nurses were willing to participate.
In addition, the study subjects were reminded via monthly emails to take their pills regularly, but the mean adherence rates were only 84% in the treatment group and 90%in the placebo group, which the researchers said were lower than in previous trials.
Furthermore, because Japan's fish consumption is higher than most other countries', the applicability of the findings on omega-3 polyunsaturated acids was questionable, especially since it had previously been reported that high fish consumption was correlated with a reduced prevalence of major depression, and diet information was not collected in this study the researchers were aiming for a pragmatic trial.
However, the researchers also wrote: "Even from the most optimistic view, the efficacy of polyunsaturated fatty acids could only lead to small effect sizes. Hence, we believe our conclusion that omega-3 polyunsaturated fatty acids are unlikely to provide benefits in terms of preventing depression, is accurate."
They concluded: "Future studies may need to investigate the association between the omega-3 : omega-6 ratio and (the) incidence of depression.
"The additive value of omega-3 polyunsaturated fatty acids was not confirmed in terms of mental state and self-evaluated work efficiency in work populations.
"We do not recommend omega-3 for the general population who are willing to maintain their mental health and are looking for something beneficial."
Source: Journal of Psychiatric Research
"Omega-3 fatty acids for a better mental state in working populations - Happy Nurse Project: A 52-week randomized controlled trial"
Authors: Norio Watanabe, et al.