Higher blood levels of omega-3 fatty acids are associated with a significantly lower risk of developing early-onset dementia, according to a major new analysis of more than 217,000 adults from the UK Biobank published in Clinical Nutrition.
The prospective study followed adults aged 40-64 for an average of 8.3 years and identified 325 cases of early-onset dementia, defined as a diagnosis before age 65.
Researchers found that individuals with higher plasma omega-3 levels had a substantially reduced risk of developing early-onset dementia compared with those who had the lowest levels.
Participants in the highest omega-3 quintiles experienced approximately a 35-40% lower risk, even after adjusting for genetic risk (APOE-ε4), lifestyle factors and cardiometabolic health variables.
"This is the first large-scale study to show that objectively measured omega-3 status is linked to lower risk of dementia diagnosed before age 65," said Dr Aleix Sala‑Vila, lead author of the study.
"Most prior research has focused on older populations."
"Our findings strongly suggest that omega-3 intake earlier in midlife may play a meaningful role in brain health decades before dementia typically appears."
Notably, the protective association was observed not only for DHA — the most abundant omega-3 fatty acid in the brain — but was even stronger for non-DHA omega-3 fatty acids, highlighting the potential importance of considering the full spectrum of omega-3s rather than focusing on DHA alone.
"These results reinforce the value of using blood biomarkers rather than self-reported diet when studying nutrition and brain health," said Dr Nathan L. Tintle, co-author of the study.
"Because omega-3 levels can be safely and effectively increased through diet and supplementation, this represents a plausible, low-cost strategy that could help reduce the burden of early-onset dementia."
The researchers also found no evidence that the association differed by APOE-ε4 genotype, suggesting that higher omega-3 status may be beneficial regardless of genetic risk.
Based on established conversion equations, omega-3 levels associated with the greatest risk reduction corresponded to an Omega-3 Index of approximately 8% — a level achievable through regular consumption of fatty fish and/or omega-3 supplements.
While the authors emphasise that the observational design does not prove causality, they note that randomised trials examining dementia incidence are unlikely to be feasible due to the rarity of early-onset dementia and the long follow-up required.
"When a safe, accessible lifestyle factor is consistently associated with lower disease risk," Sala-Vila added, "it deserves serious consideration as part of a broader prevention strategy."
The study was conducted using data from the UK Biobank and supported by public research funding agencies in Europe.