Omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) supplementation in the cardiovascular field is effective if a certain Omega-3 index (O3I) is achieved or the daily n-3 LCPUFA dose is high enough. Whether this applies to studies on cognition in children and adolescents is unclear. The aims of the current review were to investigate whether: (1) a certain O3I level and (2) a minimum daily n-3 LCPUFA dose are required to improve cognition in 4–25 year olds. Web of Science and PubMed were searched. Inclusion criteria: placebo controlled randomized controlled trial; participants 4–25 years; supplementation with docosahexaenoic acid (DHA) and/or eicosapentaenoic acid (EPA); assessing cognition; in English and ≥10 participants per treatment arm. Thirty-three studies were included, 21 in typically developing participants, 12 in those with a disorder. A positive effect on cognitive measures was more likely in studies with an increase in O3I to >6%. Half of the studies in typically developing children with daily supplementation dose ≥450 mg DHA + EPA showed improved cognition. For children with a disorder no cut-off value was found. In conclusion, daily supplementation of ≥450 mg DHA + EPA per day and an increase in the O3I to >6% makes it more likely to show efficacy on cognition in children and adolescents.

The impact of omega-3 long-chain polyunsaturated fatty acids (LCPUFAs) on cognition is heavily debated. In the current study, the possible association between omega-3 LCPUFAs in blood and cognitive performance of 266 typically developing adolescents aged 13–15 years is investigated. Baseline data from Food2Learn, a double-blind and randomized placebo controlled krill oil supplementation trial in typically developing adolescents, were used for the current study. The Omega-3 Index was determined with blood from a finger prick. At baseline, participants finished a neuropsychological test battery consisting of the Letter Digit Substitution Test (LDST), D2 test of attention, Digit Span Forward and Backward, Concept Shifting Test and Stroop test. Data were analyzed with multiple regression analyses with correction for covariates. The average Omega-3 Index was 3.83% (SD 0.60). Regression analyses between the Omega-3 Index and the outcome parameters revealed significant associations with scores on two of the nine parameters. The association between the Omega-3 Index and both scores on the LDST (β = 0.136 and p = 0.039), and the number of errors of omission on the D2 (β = −0.053 and p = 0.007). This is a possible indication for a higher information processing speed and less impulsivity in those with a higher Omega-3 Index.

Long-chain polyunsaturated fatty acids (LCPUFA) are important for brain development and function, maybe especially during adolescence. Observational studies have demonstrated an association between fish consumption (a source of LCPUFA) and cognition in adolescents, but intervention trials are lacking. The goal of the current study was to investigate the effect of one year of krill oil (a source of LCPUFA) supplementation on the cognitive performance of adolescents with a low Omega-3 Index (O3I ≤ 5%). A double-blind, randomized, and placebo-controlled supplementation trial with repeated measurements (baseline (T0), three months (T1), six months (T2), and 12 months (T3)) in adolescents (267 randomized) was executed. Participants were randomized to 400 mg eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) per day in Cohort I or placebo and 800 mg EPA + DHA per day in Cohort II or placebo. O3I was monitored by a finger prick at all time points. At T0, T2, and T3, participants executed a neurocognitive test battery. Covariate corrected mixed models were run with either condition (krill or placebo) or O3I as predictors. Krill oil supplementation led to a small but significant increase in mean O3I, but few participants increased to the intended O3I range (8–11%). There was no significant effect of supplementation on the neurocognitive tests, nor a relationship between O3I and neurocognitive test scores. The increase in O3I was small in most participants, probably due to non-compliance. Possibly the increase in O3I was too small to demonstrate an effect. More research on the influence of LCPUFAs on cognition in adolescents is needed.

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