The influence of n-3 polyunsaturated fatty acids on cognitive function in individuals without dementia: a systematic review and dose-response meta-analysis.

BACKGROUND: Omega-3 polyunsaturated fatty acids (n-3 PUFA) have been suggested as a cognitive enhancing agent, though their effect is doubtful. We aimed to examine the effect of n-3 PUFA on the cognitive function of middle-aged or older adults without dementia. METHODS: We reviewed randomized controlled trials of individuals aged 40 years or older. We systematically searched PubMed/MEDLINE, EMBASE, CINAHL, PsycINFO, and Cochrane Library databases. We used the restricted cubic splines model for non-linear dose-response meta-analysis in terms of the standardized mean difference with 95% confidence intervals. RESULTS: The current meta-analysis on 24 studies (n 9660; follow-up 3 to 36 months) found that the beneficial effect on executive function demonstrates an upward trend within the initial 12 months of intervention. This effect is prominently observed with a daily intake surpassing 500 mg of n-3 PUFA and up to 420 mg of eicosapentaenoic acid (EPA). Furthermore, these trends exhibit heightened significance in regions where the levels of blood docosahexaenoic acid (DHA) + EPA are not very low. CONCLUSIONS: Supplementation of n-3 PUFA may confer potential benefits to executive function among the middle-aged and elderly demographic, particularly in individuals whose dietary DHA + EPA level is not substantially diminished.

Hypohomocysteinemia may increases the risk of dementia and Alzheimer's disease: A nationwide population-based prospective cohort study.

BACKGROUND: Hyperhomocysteinemia has been repeatedly found to increase the risk of dementia. However, the effects of hypohomocysteinemia on the risk of dementia have been barely investigated. If hypohomocysteinemia, like hyperhomocysteinemia, increases the risk of dementia, misuse or overuse of homocysteine-lowing agents such as vitamin supplements may increase the risk of dementia. AIMS: To investigate whether hypohomocysteinemia, like hyperhomocysteinemia, could increase the risk of dementia and Alzheimer's disease (AD) in a large population-based cohort of older adults. METHODS: This prospective cohort study followed 2655 randomly sampled, community-dwelling, non-demented individuals aged 60 years or older from 2010 to 2018. We measured baseline serum total homocysteine (tHcy) levels and examined the effect of serum tHcy on the risks of dementia and AD using Cox proportional hazards models. RESULTS: During the follow-up period (mean = 5.4 years, SD = 0.9), dementia and AD developed in 85 and 64 participants, respectively. Not only the participants with high serum tHcy (≥10.6 µmol/L) but also those with low serum tHcy (≤8.9 µmol/L) were 4-5 times more likely to develop dementia and AD compared to those with serum tHcy levels between 9.0 and 10.5 µmol/L. With the increase in serum tHcy concentration, the use of vitamin supplements decreased, and 41.2% of the participants with low serum tHcy (≤8.9 µmol/L) were taking vitamin supplements. CONCLUSIONS: Not only hyperhomocysteinemia but also hypohomocysteinemia considerably increased the risk of dementia and AD in older adults. The risk of dementia that results from overuse or misuse of vitamin supplements should be acknowledged and homocysteine-lowering health policies should be tailored to consider dementia risks that are associated with hypohomocysteinemia.