When omega-3 may help mental health and when they may not

by · News-Medical

Diet and mental health

Mental disorders are among the major causes of illness worldwide. Their rising rates coincide with the dietary shift towards pro-inflammatory omega-6 fatty acids (FAs) and away from anti-inflammatory FAs. Nutritional contributors to this shift include not only relative omega-3 deficiency but also other important factors like magnesium and zinc, vegan or vegetarian diets, and reduced eating due to mental illness.

Genetic factors also play a role in fat metabolism, along with sex, age, physical activity, medications, and other lifestyle characteristics such as drinking or substance use. Women have higher levels of the omega-3 docosahexaenoic acid (DHA) than men.

Brain health and fatty acids

Both omega-3 and omega-6 FAs are polyunsaturated FAs (PUFAs). These are important membrane constituents and contribute to membrane fluidity in the living cell.

Omega-6 PUFA biosynthesis begins with linoleic acid (LA), which gives rise to arachidonic acid (AA), also found in butter, eggs, and meat, part of the typical Western diet that is omega-6-enriched. AA metabolism produces predominantly pro-inflammatory compounds.

Omega-3 FAs like eicosapentaenoic acid (EPA) and DHA occur mostly in sea fish and algae, though they can be synthesized from alpha-LA (ALA) found in chia seed and flax seed at low levels.

Dietary PUFA ratios matter

All PUFAs are metabolized by the same enzymes. At optimal omega-6: omega-3 (LA: ALA) ratios (1:1 to 4:1), these enzymes bind omega-3 FAs more efficiently than omega-6. At higher ratios, ALA conversion to long-chain omega-3 FAs decreases. This favors AA conversion to pro-inflammatory eicosanoids.

The typical Western-style diet, with a ratio as high as 20:1, may promote systemic inflammation over the long term.

The importance of omega-3

Omega-3 intake is important for fatty acid metabolism, which is often abnormal in mental illness. Besides its conversion to long-chain omega-3 FAs, ALA is itself bioactive, with potential neuroprotective and anti-inflammatory attributes.

DHA accounts for up to 40 % of PUFAs in the neuronal membranes. It regulates neurotransmission and synaptic plasticity, protects neurons against programmed cell death, and regulates gene expression. DHA metabolites help resolve neuroinflammation and improve brain resilience through their antioxidant and immunomodulatory activity. EPA is associated with anti-inflammatory and antidepressant effects and may also indirectly support cognitive processes through these mechanisms.

Omega-3 FAs may help modulate the pro-inflammatory AA pathway while promoting the anti-inflammatory ALA pathway. They act on the hypothalamic-pituitary-adrenal (HPA) axis, which regulates stress responses. By reducing stress hormone secretion, this may help limit stress-induced neuronal damage and hyperreactivity.

They help regulate neurotransmitters, which are often dysregulated in mental illness, such as serotonin and dopamine. By helping to preserve blood-brain barrier integrity, they may reduce the entry of inflammatory and neurotoxic substances. They also regulate genes involved in inflammation and fatty acid metabolism, and have been suggested to influence AD-related changes. Their positive impact on gut microbiome health may also contribute to improved brain health via the gut-brain axis.

Chronic low-grade inflammation is found in a proportion of patients suffering from several neurodegenerative and psychiatric conditions. Thus, patients with high inflammatory markers may benefit the most from omega-3 supplements, although this remains an area of ongoing research.

Omega-3 in mental health

Pharmacological agents and psychological counseling are used to treat mental illness, but with limited success. Depression remains treatment-resistant in up to 30 % of cases, while many effective drugs have high discontinuation rates because of their adverse effects.

Aberrant FA profiles and immunological abnormalities occur in multiple psychiatric disorders, ranging from schizophrenia or depression through autism spectrum disorders (ASD) to Alzheimer’s disease (AD). The current review sought to synthesize existing literature on omega-3 supplementation in mental illness.

Most of the evidence comes from short-term trials or observational studies, with mixed and sometimes conflicting findings that vary across conditions and do not establish clear causality.

Schizophrenia

Some patients with schizophrenia have altered PUFA metabolism, leading to low PUFA levels. A randomized controlled trial (RCT) suggested that young people at high risk for psychosis might safely be treated with long-term PUFA supplements to reduce the risk of progression from subclinical symptoms to overt psychosis, though findings across studies remain inconsistent.

Early psychosis might also be potentially effectively treated with omega-3 supplements, though chronic mental illness is usually considered refractory to such therapies. More recent studies suggest that they might enhance the response to medication, reduce the dosage of antipsychotic drugs, and lower the risk of extrapyramidal effects. However, these findings are largely based on short-term studies and are not consistently replicated.

Notably, this is not supported by the guidelines published by several professional bodies.

Affective disorders

Fish intake is associated with a lower risk of depression and improved depressive symptoms. However, the evidence is mostly from observational studies.

Anxiety disorder and post-traumatic stress disorder

Omega-3 deficiency may increase stress-related susceptibility to social anxiety disorders. Conversely, anxiety could account for the lower levels via decreased dietary intake.

PUFA levels may be altered in patients with post-traumatic stress disorder (PTSD), though this may not be a causal association, and clinical trials have shown limited or inconsistent preventive effects.

Eating disorders may reduce omega-6 metabolism, perhaps because starvation-induced reductions in enzymatic activity limit omega-6 conversion into its long-chain derivatives. Despite the appetite-stimulating and neuroprotective effects of omega-3 supplementation, there is limited evidence that it helps treat anorexia nervosa, with meta-analyses showing no consistent improvement in core psychological symptoms.

Neurodevelopmental disorders

These typically become obvious in early childhood, and ASD often coexists with attention-deficit hyperactivity disorder. Unbalanced dietary habits and skewed PUFA ratios may contribute to these disorders.

Encouraging maternal intake of omega-3 fatty acids, especially DHA, may be beneficial, particularly in cases of deficiency, but evidence for prevention remains limited and context-dependent. There is little evidence that supplementation in childhood and adolescence improves symptoms independently or in combination with other non-pharmacological therapies.

Neurodegenerative disease

DHA is crucial to brain health, but AD patients do not have significantly lower levels than others. However, long-term omega-3 supplementation could be an effective preventive measure when initiated before or in the very early stages of cognitive decline. Thus, targeted supplementation might be useful in preventing mild cognitive impairment or very mild AD.

It is probably ineffective in advanced AD, perhaps explained by the influence of multiple factors that reduce brain uptake of DHA despite supplementation.

Implications

Mental illness is also associated with other disorders like cardiovascular disease and type 2 diabetes mellitus. Future research should clarify whether abnormal fatty acid metabolism is a cause or consequence of mental illness, or an associated finding.

PUFA ratio may be a potential biomarker of mental illness. Meanwhile, the safety, tolerability, low cost, and healthfulness of omega-3 FAs make them a potentially useful adjunct in the prevention and treatment of mental disorders. The lack of evidence-based guidelines and poor regulatory oversight mandate their use under medical supervision.

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