Featured in Science Digest #164

Higher omega-3 levels are linked to lower risk of early-onset dementia. Digest

doi.org
2 min read •

Dementia that develops before age 65, often called early-onset dementia, is relatively rare but can profoundly disrupt cognitive function, independence, and daily life for both individuals and their families. Many cases appear to be influenced by lifestyle factors, yet diet has received little attention in this younger age group. To address this gap, researchers examined whether blood levels of omega-3 fatty acids in midlife are associated with the later development of early-onset dementia.

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Using data from the UK Biobank, the team studied more than 217,000 adults between ages 40 and 64 who did not have dementia at the start of the study and were followed for an average of about eight years to track new dementia diagnoses recorded in hospital and death records. Instead of relying on food questionnaires, they analyzed omega-3 levels measured in participants' blood. The researchers focused on three measures: total omega-3 fatty acids, docosahexaenoic acid (DHA, the most abundant omega-3 in the brain), and non-DHA omega-3s, which include other omega-3 fatty acids found in fish and plant foods.

  • During follow-up, 325 participants developed early-onset dementia, representing about 0.15% of the study population.
  • Participants in the fourth and fifth quintiles of blood omega-3 had about a 38% and 36%, respectively, lower risk of early-onset dementia compared with those in the lowest quintile.
  • DHA on its own showed a less consistent and robust association. Although the highest DHA quintile had about a 35% lower risk than the lowest, no clear reductions were seen across the middle quintiles.
  • Non-DHA omega-3 fatty acids showed the strongest association. Participants with moderate to high levels of non-DHA fatty acids had a 37-42% reduction in risk compared with those with the lowest levels.
  • The link between omega-3 levels and dementia risk did not differ meaningfully based on APOE ε4 status, so the pattern looked broadly similar in carriers and non-carriers.

Omega-3 fatty acids are biologically linked to dementia risk because they are used to make signaling molecules that actively regulate inflammation, including inflammation within the brain. Chronic brain inflammation is increasingly recognized as a contributor to neurodegeneration. Experimental studies also show that omega-3s influence processes such as the generation of new neurons and the stability and function of neuronal membranes. In this study, stronger associations for total and non-DHA omega-3, compared with DHA alone, suggest that omega-3 fatty acids beyond DHA may meaningfully contribute to these mechanisms, consistent with evidence that different omega-3 types act through overlapping but not identical biological pathways.

Taken together, the study further strengthens the biological and epidemiological case for omega-3 fatty acids as a plausible, low-risk target for future prevention research, particularly in midlife. In this clip, Dr. Axel Montagne discusses how the brain transport of omega-3 DHA may be important for the prevention and possibly as a therapy for dementia.