Providing male rats deficient in iron and n-3 fatty acids with iron and alpha-linolenic acid alone affects brain serotonin and cognition differently from combined provision

Effect of walnut consumption on neuropsychological development in healthy adolescents: a multi-school randomised controlled trial

Background

Omega-3 fatty acids are critical for neuropsychological functioning. Adolescence is increasingly believed to entail brain vulnerability to dietary intake. The potential benefit on adolescent neurodevelopment of consuming walnuts, a source of omega-3 alpha-linolenic acid (ALA), remains unclear.

Methods

We conducted a 6-month multi-school-based randomised controlled nutrition intervention trial to assess whether walnut consumption has beneficial effects on the neuropsychological and behavioural development of adolescents. The study took place between 04/01/2016 and 06/30/2017 in twelve different high schools in Barcelona, Spain (ClinicalTrials.gov Identifier: NCT02590848). A total of 771 healthy teenagers aged 11-16 years were randomised into two equal groups (intervention or control). The intervention group received 30 g/day of raw walnut kernels to be incorporated into their diet for 6 months. Multiple primary endpoints concerning neuropsychological (working memory, attention, fluid intelligence, and executive function) and behavioural (socio-emotional and attention deficit hyperactivity disorder [ADHD] symptoms) development were assessed at baseline and after intervention. Red blood cell (RBC) ALA status was determined at baseline and 6 months as a measure of compliance. Main analyses were based on intention-to-treat using a linear mixed-effects model. A per-protocol effect of the intervention was analysed using inverse-probability weighting to account for post-randomisation prognostic factors (including adherence) using generalised estimating equations.

Findings

In intention-to-treat analyses, at 6 months there were no statistically significant changes between the intervention and control groups for all primary endpoints. RBC ALA (%) significantly increased only in the intervention group, coefficient = 0.04 (95% Confidence Interval (CI) = 0.03, 0.06; p < 0.0001). The per-protocol (adherence-adjusted) effect on improvement in attention score (hit reaction time variability) was -11.26 ms (95% CI = -19.92, -2.60; p = 0.011) for the intervention group as compared to the control group, improvement in fluid intelligence score was 1.78 (95% CI = 0.90, 2.67; p < 0.0001), and reduction of ADHD symptom score was -2.18 (95% CI = -3.70, -0.67; p = 0.0050).

Interpretation

Our study suggested that being prescribed eating walnuts for 6 months did not improve the neuropsychological function of healthy adolescents. However, improved sustained attention, fluid intelligence, and ADHD symptoms were observed in participants who better complied with the walnut intervention. This study provides a foundation for further clinical and epidemiological research on the effect of walnuts and ALA on neurodevelopment in adolescents.

Funding

This study was supported by Instituto de Salud Carlos III through the projects 'CP14/00108, PI16/00261, PI21/00266' (co-funded by European Union Regional Development Fund 'A way to make Europe'). The California Walnut Commission (CWC) has given support by supplying the walnuts for free for the Walnuts Smart Snack Dietary Intervention Trial.

Iron deficiency and internalizing symptom severity in unmedicated adolescents: a pilot study

BACKGROUND

Iron plays a key role in a broad set of metabolic processes. Iron deficiency is the most common nutritional deficiency in the world, but its neuropsychiatric implications in adolescents have not been examined.

METHODS

Twelve- to 17-year-old unmedicated females with major depressive or anxiety disorders or with no psychopathology underwent a comprehensive psychiatric assessment for this pilot study. A T1-weighted magnetic resonance imaging scan was obtained, segmented using Freesurfer. Serum ferritin concentration (sF) was measured. Correlational analyses examined the association between body iron stores, psychiatric symptom severity, and basal ganglia volumes, accounting for confounding variables.

RESULTS

Forty females were enrolled, 73% having a major depressive and/or anxiety disorder, 35% with sF < 15 ng/mL, and 50% with sF < 20 ng/mL. Serum ferritin was inversely correlated with both anxiety and depressive symptom severity (r = -0.34, p < 0.04 and r = -0.30, p < 0.06, respectively). Participants with sF < 15 ng/mL exhibited more severe depressive and anxiety symptoms as did those with sF < 20 ng/mL. Moreover, after adjusting for age and total intracranial volume, sF was inversely associated with left caudate (Spearman's r = -0.46, p < 0.04), left putamen (r = -0.58, p < 0.005), and right putamen (r = -0.53, p < 0.01) volume.

CONCLUSIONS

Brain iron may become depleted at a sF concentration higher than the established threshold to diagnose iron deficiency (i.e. 15 ng/mL), potentially disrupting brain maturation and contributing to the emergence of internalizing disorders in adolescents.

Effects of plant-based versus marine-based omega-3 fatty acids and sucrose on brain and liver fatty acids in a mouse model of chemotherapy

Chemotherapy can result in toxic side effects in the brain. Intake of marine-based omega-3 polyunsaturated fatty acids (n-3 PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), alter brain fatty acids, potentially improving brain function. However, it is unclear if alpha-linolenic acid (ALA), the plant-based n-3, affects brain PUFAs during chemotherapy. The objective of this study was to examine the effects of dietary ALA, EPA and DHA, with high or low sucrose, on brain PUFAs in a mouse model of chemotherapy. Secondarily, the use of liver PUFAs as surrogate measures of brain PUFAs was examined. Lipid peroxidation (4-HNE) and neurotrophic markers (BDNF) were assessed. Female C57Bl/6 mice (n = 90) were randomized to 1 of 5 diets (high EPA + DHA/high or low sucrose, high ALA/high or low sucrose, or control with no EPA + DHA/low ALA/low sucrose) and injected with doxorubicin-based chemotherapy or saline. Brain EPA and DHA were greater (p < 0.0001) with high EPA + DHA diets, regardless of sucrose; there were no significant differences in brain PUFAs between high ALA diets and control. Chemotherapy-treated mice had higher brain and liver DHA (p < 0.05) and lower brain and liver linoleic acid (p < 0.0001). Brain n-3 and n-6 PUFAs were strongly correlated with liver n-3 (r = 0.8214, p < 0.0001) and n-6 PUFAs (r = 0.7568, p < 0.0001). BDNF was correlated with brain total PUFAs (r = 0.36; p < 0.05). In conclusion, dietary ALA in proportions approximately two times greater than consumed by humans did not appreciably increase brain n-3 PUFAs compared to low ALA intake. Liver PUFAs may be a useful surrogate marker of brain PUFAs in this mouse model.

Influence of iron-deficient diets during gestation and lactation on cerebral fatty acids and eicosanoids in guinea pig offspring-Comparison of studies with different sources of dietary lipids

Previous studies showed that mild iron deficiency anaemia (IDA) induced by feeding an iron deficient (ID) diet to female guinea pigs during gestation and lactation to alters the auditory functions of the offspring when corn oil is the only source of dietary lipids. Conversely, feeding an ID diet with a dietary fatty acid composition similar to that of typical human western diets induced minor impairments. Since tissue fatty acid metabolism is affected by dietary iron, the current study measured the impacts of these ID diets (ID-corn and ID-west) compared to the corresponding iron-sufficient control diets (IS-corn and IS-west) on encephalum fatty acid metabolism in the offspring at post-natal day 24. IDA induced by the ID-corn diet resulted in significant increases in encephalum n-6 PUFA content, but IDA induced by the ID-west diet had little impact on fatty acid profiles compared to the IS-west group. Brain COX II protein expression and FADS2 mRNA expression were statistically unaffected in both experiments, but encephalum PGE₂ concentrations were significantly reduced in ID-west pups. These results suggest IDA studies during prenatal development should consider dietary lipid compositions.

Omega-3 Polyunsaturated Fatty Acids and Oxylipins in Neuroinflammation and Management of Alzheimer Disease

Alzheimer disease (AD) is becoming one of the most prevalent neurodegenerative conditions worldwide. Although the disease progression is becoming better understood, current medical interventions can only ameliorate some of the symptoms but cannot slow disease progression. Neuroinflammation plays an important role in the advancement of this disorder, and n-3 (ω-3) polyunsaturated fatty acids (PUFAs) are involved in both the reduction in and resolution of inflammation. These effects may be mediated by the anti-inflammatory and proresolving effects of bioactive lipid mediators (oxylipins) derived from n-3 PUFAs [eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in fish oil. Although interventions have generally used fish oil containing both EPA and DHA, several studies that used either EPA or DHA alone or specific oxylipins derived from these fatty acids indicate that they have distinct effects. Both DHA and EPA can reduce neuroinflammation and cognitive decline, but EPA positively influences mood disorders, whereas DHA maintains normal brain structure. Fewer studies with a plant-derived n-3 PUFA, α-linolenic acid, suggest that other n-3 PUFAs and their oxylipins also may positively affect AD. Further research identifying the unique anti-inflammatory and proresolving properties of oxylipins from individual n-3 PUFAs will enable the discovery of novel disease-management strategies in AD.