Across 3 studies, 1 reported a small beneficial effect of selenium on cognitive function, while 2 found neutral results. The beneficial finding came from a large observational study in adults aged 60+ years, showing a small positive association between blood selenium levels and cognitive scores. The evidence base is too small and mixed to draw firm conclusions.
Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. The only beneficial finding is from an observational study, which cannot establish causation; no RCTs or meta-analyses of selenium supplementation specifically were identified.
showed limited influence on vitamin D, lipids, or kMCT effects
Blood Se levels were positive associations with cognitive scores (β=0.049, 95% CI: 0.022, 0.076) and all four cognitive domains.
Mixed results were seen for omega (ω)-3, tea, and plant extracts