Table 1. The characteristics of the nine articles included in our study.

PAL: paired associate learning; DHA: docosahexaenoic acid; EPA: eicosapentaenoic acid; RVIP: rapid visual information process; PUFAs: omega-3 polyunsaturated fatty acids; ANOVA: analysis of variance.

Author's name and publication date	Participant numbers and mean ages	Dose information	Main findings
Yurko-Mauro et al. [9], May 2010	Total number: 485 Mean age: 70	In this study, participants received 900 mg/day of DHA or a placebo.	At 24 weeks, there were substantially fewer PAL six-type errors with DHA than with placebo (difference rating, −1.63 ± 0.76 (−3.1, −0.14, 95% CI), P = 0.03). Consumption of DHA was connected to improved rapid and late recognition memory grades (P<0.02) but not with better work memory or functioning assessments. In participants with DHA, serum DHA concentrations quadrupled and were associated with better PAL scores (P<0.02). DHA was well-tolerated, and no major side effects were recorded. A 24-week period of a 900 mg/day dose of DHA enhanced learning and memory performance in patients and is a valuable supplement that improves cognitive health as people age.
Jackson et al. [10], January 2012	Total number: 65 (16 men and 49 women) Age range: 1-29 Mean age: 20	This study compared the impact of 12 weeks of daily docosahexaenoic acid in fish oil (1 g or 2 g) versus placebo supplements (olive oil).	During cognitive activities, supplementation with both doses of fish oil resulted in considerably higher levels of oxyhemoglobin and overall hemoglobin levels, indicating improved blood circulation. Changes did not consistently follow variations in hemodynamic response to activities in cognitive function. The ANOVA revealed that fish oil treatment had a significant impact on oxyhemoglobin (F(2, 59) = 3.54, P<0.05). Post-hoc analyses of total treatment indicated that the 2 g fish oil group had substantially higher levels of oxyhemoglobin when doing an activity (P<0.05) than the placebo group. According to the comparisons performed, 2 g of fish oil was significantly (all P<0.001) performance-related and elevated total hemoglobin during each activity. Still, substantially higher levels of total hemoglobin were only observed during the Stroop and RVIP task periods for the 1 g group of fish oil. In contrast to the placebo group, consuming both doses of fish oil resulted in a considerable rise in oxyhemoglobin and total hemoglobin levels, indicating greater blood circulation during cognitive activities. Effects on cognitive function did not consistently follow hemodynamic changes in activity.
Witte et al. [11], June 2013	Total number: 65 Age range: 50-75 Mean age: 63.9	In this study, participants received 2.2 g/day of fish oil for 26 weeks (four daily pills), and the placebo capsules were sunflower.	Subjects in the omega-3 group had a significantly higher percentage of DHA and EPA assessed on erythrocyte membranes in blood plasma after treatment, compared to controls. Supplementation caused a rise in EPA percentages (Wilcoxon test, T = 4.3, P<0.001), while a reduction was indicated in the placebo group (Wilcoxon test, T = −3.2, P<0.05). Post-hoc t-tests revealed that the omega-3 supplement improved executive functions by 26%, while the placebo did not affect performance. Regarding composite memory grade, both groups had a comparable impact on the retest at follow-up with no significant group impact. This interventional investigation found that after 26 weeks of excessive amounts of marine omega-3, the executive performance of older adults improved compared to the placebo group. Overall, omega-3 and fasting insulin levels were linked to cognitive improvements.
Konagai et al. [12], September 2013	Total number: 45 (all male) Age range: 61-72	This study used three different kinds of experimental additives: krill oil as a PUFAS-rich oil mixed with phosphatidylcholine, sardine oil, and triglycerides as a placebo.	For 12 weeks, the groups that were given krill oil or sardine oil exhibited higher oxyhemoglobin content in channel ten than in the group that was given triglycerides. The krill oil group showed considerably higher oxyhemoglobin levels in the brain's frontal region than the triglyceride sample. This research suggests that n-3 PUFAs improve cognition in the elderly.
Bauer et al. [13], January 2014	Total number: 13 (four men and nine women) Age range: 20-24	This supplementation study used two distinct fish oil meals. The first diet (Eye-QTM, Novasel) contained a high EPA: DHA ratio, while the second diet (EfalexTM, Efamol) had a high DHA: EPA ratio. Participants took six pills daily as a supplement.	The results showed a decrease in the functional activity of the cingulate cortex and an improvement in the right precentral gyrus after the EPA-rich dose, as well as a reduction in response times on the Stroop task with color words Stroop. On the contrary, DHA increased right precentral gyrus activity in spatial cognition tasks but did not affect behavioral performance. It was found that after EPA-rich supplementation, individuals' brains performed with less difficulty and had higher cognitive performance than before supplementation. In contrast, the increase in functional induction and the absence of progress in cognitive performance in time after DHA may demonstrate that DHA is much less helpful than EPA in improving neurocognitive functioning after one month.
Jaremka et al. [14], October 2014	Total number: 138 (67% female) Age range: 51.04	In this study, participants received 1.25 g of omega-3 or 2.5 g of omega-3 per day for four months.	Lonelier participants in the placebo group exhibited worse episodic memory after dosage, as judged by instant (b = 0.28, t (117) = 2.62, p = 0.010) and long delay (b = 0.06, t (116) = 2.07, p = 0.040) free recall. This impact was not observed in the 1.25 g/day or 2.5 g/day supplementation groups, with p-values greater than 10. Plasma omega-ratio data confirmed these findings. There was no difference between omega-3 on short-delay recollection or other cognitive tests associated with loneliness, with all p-values greater than 0.32. The loneliness impact was not found in people taking 1.25 g or 2.5 g of omega-3 daily. Compared to the placebo group, lonelier individuals demonstrated greater instant free recall when taking the omega-3 supplement dose of 2.5 g/day. Increases in the plasma omega-6: the omega-3 ratio was associated with moderately superior immediate and long-latency-free recall in lonelier subjects. Lonelier people lose episodic memory over time. Loneliness-related episodic memory impairments were reduced by omega-3 supplementation, especially at a high dose (2.5 g/day). Lonelier people who received the placebo showed lower episodic verbal memory than less lonely ones, regardless of baseline scores. Users of omega-3 did not have this impact. Lonelier supplement users exhibited stronger verbal episodic memory than placebo users. Supplements boosted verbal and episodic memory.
Külzow et al. [15], March 2016	Total number: 44 (all female) Age range: 50-75	In this study, the omega-3 fatty acid group was given four fish-oil pills daily for 26 weeks. Four pills daily included 2200 mg of omega-3. The placebo group received four daily pills containing 1015 mg of sunflower oil.	An increase in omega-3 indexes, higher proportions of EPA, and DHA in peripheral blood erythrocytes led to a significantly enhanced recall of relevant object location associations for the omega-3 group versus the placebo group, without significantly changing learning and response time. Omega-3 improves the memory of elderly people. Omega interventions are valuable, well-tolerated, and safe.
Leckie et al. [16], October 2019	Total number: 271 (118 men and 153 women) Age range: 30-54 Mean age: 43	Participants in this study received 300 mg per day of omega-3, which was taken for 18 weeks via fish-oil capsules, or they received a placebo.	EPA and DHA concentrations in red blood cells rose as predicted, and capsule compliance was greater than 95%. No cognitive domain was affected by the supplement. Fish-oil treatment improved executive function in people with low baseline DHA levels compared with the placebo group. No changes in brain morphology were observed. A moderate dose of omega-3 for a moderate period did not impact neuropsychological function or brain morphology.
Maltais et al. [17], March 2022	Total number: 193 Age range: 20-80	Supplemental omega-3 is taken via four pills per day. Placebo pills contain high-oleic soybean or corn oil with no DHA or EPA.	After six months of omega-3, four cognitive domains of healthy participants did not vary between groups. Participants with low episodic memory improved significantly with omega-3 (p = 0.043). Cognitively healthy people did not benefit from a six-month dose of omega-3, and apolipoprotein E status or age had no influence.