Omega-3 is inversely related to risk of early-onset dementia

Original Article ↗ Hacker News Discussion ↗

Study result & effect size

  • Thread focuses on a large UK Biobank cohort finding lower early‑onset dementia (EOD) incidence in higher omega‑3 blood quintiles.
  • Absolute risk is tiny: ~0.193% in lowest quintile vs ~0.116% in highest over 8.3 years — about a 40% relative reduction, but only 0.08 percentage‑points in absolute terms.
  • Some see this as still meaningful (halving a terrifying outcome), others argue this will be overhyped by media.

Mechanisms & different omega‑3s

  • Several comments attribute benefits to reduced inflammation, oxidative stress, and vascular/fibrotic effects.
  • Discussion around DHA vs non‑DHA omega‑3: non‑DHA signal appears stronger in the paper, which confuses people given the usual DHA‑centric narrative.
  • Clarification: plant ALA can convert to EPA/DHA but inefficiently (especially in older adults and males). Some suggest non‑DHA effect may be driven by other long‑chain omega‑3s, not ALA alone.

Food vs supplements; fish vs algae

  • Many emphasize fish (especially fatty fish like salmon, mackerel, sardines) as established sources; randomized trials of generic supplements often show modest or null effects.
  • Others highlight algal (“algal oil”) EPA/DHA as chemically similar to fish‑derived, noting that fish get omega‑3s from algae anyway.
  • Concerns raised about supplement quality (low dose, rancidity, contaminants) and algal oil cost; some argue it’s effectively a “health tax.”

Vegan, ethics, and “evolutionary” arguments

  • Large sub‑thread debates meat vs plant‑based diets:
    • One side appeals to “we evolved to eat meat” and rejects replacing food with pills.
    • Counterarguments: evolution isn’t a moral guide; humans are omnivores; intensive animal farming is cruel; plant‑based diets can be healthy.
    • Mussels and algae are floated as “ethically easier” high‑omega‑3 options.

Practical guidance & comorbidities

  • Commenters ask: how much fish or omega‑3 is needed? Answers are vague: often framed as 1–2 servings of fatty fish per week, but “unclear” is acknowledged.
  • Atrial fibrillation risk from omega‑3 is debated; one commenter suggests risk appears dose‑dependent and would consult a doctor but notes doctors often oversimplify.

Omega‑6, ratios, and broader diet

  • Some repeat “omega‑3 good, omega‑6 bad” or emphasize n3:n6 ratios and seed oils.
  • Others push back, saying evidence for harmful high omega‑6 (at adequate omega‑3 levels) is weak.
  • Several note that “benefits of fish” may partly be displacement of worse foods and correlates of home cooking or healthier lifestyles.

Study design, statistics & causality

  • Skeptics stress this is observational, based mostly on a single blood draw, with potential confounding (wealth, health consciousness, culture, ancestry).
  • Discussion of statistical issues: attenuation bias from noisy measurement, p‑hacking, publication bias, prior failures of nutritional epidemiology vs RCTs.
  • One counterpoints that, in aggregate, intake‑based observational and trial results align fairly often, so replicated epidemiology can still inform causal beliefs.

Insurance & societal implications

  • Actuarial commenters note that robust links between biomarkers and EOD could materially change long‑term care pricing, risk pooling, and even threaten the viability of some insurance products.
  • This sparks a broader debate about fairness of risk‑based pricing vs social solidarity, and how improved prediction can undermine traditional insurance.