In January 2018 researchers from the USA published their review of the medical scientific literature to assess the effect of over-the-counter supplements on cognitive decline, mild cognitive impairment and Alzheimer-type dementia. A total of 38 studies were included in the review and compared either omega-3 polyunsaturated fatty acids, soya, ginkgo biloba, B vitamins, vitamin D plus calcium, vitamin C or beta-carotene, multi-ingredient supplements, or other over-the-counter preparations with placebo or other supplements. It was noted that these generally had a low to medium risk of bias. Results showed that over-the counter-supplements provided no benefit on Alzheimer-type dementia or mild cognitive impairment. Daily folic acid plus vitamin B12 was associated with improvements in performance in some memory tests but these were not clinically significant. Moderate-strength evidence revealed that vitamin E had no benefit on cognition whilst evidence on the effects of omega-3 polyunsaturated fatty acids, soya, ginkgo biloba, folic acid alone or with other B vitamins, beta-carotene, vitamin C, vitamin D plus calcium, and multivitamins or multi-ingredient supplements was either insufficient or of low quality, suggesting that these supplements did not reduce risk of cognitive decline.
Butler M et al. Over-the-Counter Supplement Interventions to Prevent Cognitive Decline, Mild Cognitive Impairment, and Clinical Alzheimer-Type Dementia: A Systematic Review. Ann Intern Med. 2018 Jan 2;168(1):52-62