Does taking omega-3 supplements reduce the risk of having depression or anxiety? Probably not

Depression is the leading course of disability, and many patients with depression also suffer from anxiety symptoms. Research has shown that people with depression have a lower level of omega-3 polyunsaturated fatty acids (PUFA) compared with the general population, and data from observational studies suggest that dietary supplementation with long chain fatty acids (PUFA) can lower the risk of developing depression or anxiety.

In a recent systematic review, the authors assessed the effect of omega-3 PUFA supplementation on the risk of anxiety and depression using evidence from randomised clinical trials (RCTs). They included trials lasting at least 6 months with adults who were not seriously ill or pregnant. The included studies compared omega-3 PUFA supplementation versus usual diet, no advice, no supplementation or placebo. Their primary outcome was the risk of depression or anxiety based on a formal diagnosis or use of an appropriate scale.

In total, 31 trials (n=41 470) were included. There was no significant difference in the risk of depression with omega-3 PUFA supplementation compared with controls (13 trials, n=26 528): Risk ratio (RR) 1.01, 95% CI 0.92 to 1.10, moderate-quality evidence. Only one study reported data on the risk of anxiety with omega-3 PUFA supplementation and the study found no significant difference: RR 1.00, 95% CI 0.32 to 3.10.

The review authors conducted extensive searches to identify relevant studies, and the assessed the quality of studies using standardised criteria. They also conducted several subgroup analyses to assess the effect of various subtypes of omega-3 PUFA on their outcomes. Heterogeneity was low for most of the meta-analyses. However, the review did not include subjects with depression, and there was lack of information on the baseline PUFA intake in the included trials.

The findings of this review contradict those of observational studies that suggest an inverse relationship between omega-3 PUFA intake and the risk of depression and anxiety. Of note, those reviews had substantial heterogeneity in their meta-analyses, coupled with inherent low quality of observational studies compared with RCTs. Current evidence does not support use of omega-3 PUFA for reducing the risk of depression and anxiety.

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