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13th November 2015

Depressed – Perhaps you need a portion of oily fish?

We have written frequently on nutrition and dementia in previous blogs, but we haven’t touched so much on another prevalent health issue with regards to cognitive health, that of depression.

Depression is prevalent in care homes

Depression is the most common mental health problem of later life. Older people in residential and nursing homes are more likely to experience depression than older people in the community, affecting some 10-20 percent of older people and up to 40 percent of care home residents. Yet in older people depression is often under-diagnosed and under-treated.

Major depressive disorder (MDD) is characterised by depressed mood and/or a markedly decreased pleasure or interest in all activities. One suggested treatment for MDD has been omega-3 fatty acids, naturally found in fatty fish, some other seafood and some nuts and seeds.

Researchers have reported that a deficiency of omega-3 is associated with dysfunction in the membranes of nerve cells and the neurotransmitters, serotonin, norepinephrine and dopamine – the ‘message carriers’ in the brain. This proposed mechanism might go some way in explaining why low omega-3 intake could lead to the impairment of mood and cognition noted in depression. Some studies suggest that omega-3 supplements may have a beneficial impact on depressive symptoms, but the research is remarkably inconsistent.

Omega-3 fatty acids for depression

The most recent publication on the subject, the Cochrane Review, Omega-3 fatty acids for depression in adults, concludes that there is insufficient evidence for omega-3 supplements in treating major depressive disorder. This review gathered data from 25 randomised trials involving 1438 participants that compared the impact of omega-3 supplements with placebo, and one study (40 subjects) that compared the effect of omega-3 with antidepressants.

The researchers reported that people given omega-3 supplements had lower depressive symptom scores than those people taking a placebo.

However, it is important when we interpret results that we consider whether differences, even statistically significant as reported here, translate to significant clinical benefits. In other words, would the size of the effect be meaningful to people with depression?  The authors concluded from this review it would not, and that the effect was small. Furthermore the evidence was described as low or very low quality, therefore undermining confidence in the positive result.

At present then, we do not have enough high quality evidence to determine the effects of omega-3 fatty acids as a treatment for MDD. An area of important research for the future would be in looking more closely at individuals who may or may not benefit from such supplement treatment, so that we may be more able to understand or explain differences in study findings.

In the meantime including oily fish on the menu is still a good idea.

Ayela Spiro, British Nutrition Foundation – QCS Expert Nutrition Contributor

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