Adolescence is an important period for cognitive maturation and emotional regulation, and this age group is particularly vulnerable to developing depression. Diets rich in fruits and vegetables have been associated with decreased risk of developing depressive disorders across the lifespan, maybe due to the high flavonoid content of these foods. Previously, we have shown increases in transient positive affect (PA) in both children and young adults 2 h after administration of a wild blueberry (WBB) intervention. Here, using a randomised double-blind, placebo-controlled trial, we investigated the effects of 4 weeks, daily WBB supplementation (containing about 253 mg anthocyanins) on transient and chronic mood in adolescents. Healthy 12–17-year old (n 64, thirty-five females) participants were randomly assigned to receive either a WBB or matched placebo supplementation. Depression and anxiety symptoms were assessed before and after the intervention period using the Mood and Feeling Questionnaire and Revised Child Anxiety and Depression Scale. Transient affect was assessed before, 2 weeks and at 4 weeks using PA and negative affect. Following the intervention period, there were significantly fewer self-reported depression symptoms in participants who were supplemented with WBB compared with placebo (P = 0·02, 95 % CI –6·71, –5·35). There was no between-group effect on anxiety symptoms or on transient affect. Further investigation is required to identify specific mechanisms that link flavonoids consumption and mood. If replicated, the observed effects of WBB supplementation may be a potential prevention strategy for adolescent depression and may have benefits for public mental health.

Evidence suggests that low folate status may be detrimental to mood and associated with depleted cerebrospinal fluid levels of the neurotransmitter serotonin (5-hydroxytryptamine; 5-HT). A placebo-controlled trial was carried out to determine the effect of folic acid supplementation (100 μg for 6 weeks followed by 200 μg for a further 6 weeks) upon subjective mood (Positive and Negative Affect Schedule) and biochemical markers of mood (5-HT) in healthy males (n 23). Blood samples were obtained at baseline (week 0) and during the intervention at week 6 and week 12. Subjective mood assessments were obtained at week 0 and week 12. The results showed an increase in serum and erythrocyte folate concentrations (P=0·02 and P=0·003, respectively) and a corresponding decrease in plasma homocysteine (P=0·015) in response to the folic acid intervention. Neither subjective mood nor 5-HT levels, however, were significantly altered in response to the change in folate status. Folic acid given at physiological doses did not appear to improve the mood of healthy folate-replete individuals over a 12-week period. Further research is needed to address the effect of folic acid supplementation or of longer duration or increased dose, particularly in the face of sub-optimal folate status.