Optimal interventions to prevent or delay cognitive decline, mild cognitive impairment (MCI), or dementia are uncertain.

To summarize the evidence on efficacy and harms of over-the-counter (OTC) supplements to prevent or delay cognitive decline, MCI, or clinical Alzheimer-type dementia in adults with normal cognition or MCI but no dementia diagnosis.

Multiple electronic databases from 2009 to July 2017 and bibliographies of systematic reviews.

English-language trials of at least 6 months' duration that enrolled adults without dementia and compared cognitive outcomes with an OTC supplement versus placebo or active controls.

Extraction performed by a single reviewer and confirmed by a second reviewer; dual-reviewer assessment of risk of bias; consensus determination of strength of evidence.

Thirty-eight trials with low to medium risk of bias compared ω-3 fatty acids, soy, ginkgo biloba, B vitamins, vitamin D plus calcium, vitamin C or β-carotene, multi-ingredient supplements, or other OTC interventions with placebo or other supplements. Few studies examined effects on clinical Alzheimer-type dementia or MCI, and those that did suggested no benefit. Daily folic acid plus vitamin B₁₂ was associated with improvements in performance on some objectively measured memory tests that were statistically significant but of questionable clinical significance. Moderate-strength evidence showed that vitamin E had no benefit on cognition. Evidence about effects of ω-3 fatty acids, soy, ginkgo biloba, folic acid alone or with other B vitamins, β-carotene, vitamin C, vitamin D plus calcium, and multivitamins or multi-ingredient supplements was either insufficient or low-strength, suggesting that these supplements did not reduce risk for cognitive decline. Adverse events were rarely reported.

Studies had high attrition and short follow-up and used a highly variable set of cognitive outcome measures.

Evidence is insufficient to recommend any OTC supplement for cognitive protection in adults with normal cognition or MCI.

Agency for Healthcare Research and Quality.

预防或延迟认知能力下降，轻度认知障碍（MCI）或痴呆症的最佳干预措施尚不确定。

总结非处方药（OTC）补充剂预防或延迟认知正常或MCI但无痴呆诊断的成年人的认知功能下降，MCI或临床阿尔茨海默氏痴呆的功效和危害的证据。

从2009年到2017年7月的多个电子数据库，以及系统评价书目。

至少持续6个月的英语试验招募了没有痴呆症的成年人，并比较了OTC补充剂与安慰剂或积极对照组的认知结局。

由一名审稿人进行提取并由另一名审稿人确认；双重审查者对偏见风险的评估；共识确定证据的力量。

38项偏低至中度偏倚风险的试验比较了ω-3脂肪酸，大豆，银杏叶，B族维生素，维生素D加钙，维生素C或β-胡萝卜素，多成分补充剂或其他OTC干预与安慰剂或其他补品。很少有研究检查对临床阿尔茨海默氏型痴呆或MCI的影响，但确实没有益处。每日叶酸加维生素B ₁₂与一些客观测量的记忆测试的性能改善相关，这些测试具有统计学意义，但临床意义值得怀疑。中等强度的证据表明维生素E对认知没有益处。关于ω-3脂肪酸，大豆，银杏叶，叶酸或单独与其他B族维生素，β-胡萝卜素，维生素C，维生素D加钙以及多种维生素或多种成分补充剂的影响的证据不足或强度低，表明这些补品并未降低认知能力下降的风险。不良事件很少报道。

研究人员流失率高，随访时间短，并且使用了一系列差异很大的认知结果指标。

证据不足以推荐任何OTC补充剂用于具有正常认知或MCI的成年人的认知保护。

医疗保健研究与质量局。