A scoping review screened 803 records and kept 12 studies (8 randomised trials, 3 cohorts, 1 open-label trial) testing antioxidant-containing immunonutrients in older adults with mild cognitive impairment or dementia. Signals appeared for tocopherols, vitamins A and D3, carotenoids such as lutein and zeaxanthin, and omega-3 and omega-6 fatty acids. Folic acid combined with vitamin B12 showed the strongest cognitive effects, followed by DHA and EPA, with the largest gains in people already diagnosed with impairment or mild dementia.
Treat this as a map of the literature, not a verdict. Scoping reviews do not pool effect sizes or grade bias, and twelve heterogeneous studies spanning many nutrients, doses and endpoints cannot support firm claims. The B-vitamin finding fits earlier trials, notably VITACOG, where B vitamins slowed brain atrophy mainly in people with elevated homocysteine, which suggests benefit depends on baseline status. The omega-3 story is similar: strongest in those already symptomatic, while large trials in cognitively healthy adults have mostly been null. Vitamin E has an uneven record, with high-dose trials raising safety concerns. The practical reading for adults is modest: correcting a B12 or folate deficiency is worthwhile, and a diet rich in oily fish and colourful vegetables is low-risk, but supplement stacks are unproven for preventing decline. Anyone with memory concerns should have B12 and homocysteine checked rather than self-prescribing. Overall, this is confirmatory and incremental, mainly useful for showing where better-designed trials are still missing.