A biphasic response to blueberry supplementation on depressive symptoms in emerging adults: a double-blind randomized controlled trial

Double-blind randomized controlled trial in emerging adults with self-reported moderate-to-severe depressive symptoms recruited from the University of Reading student community in the United Kingdom. The active blueberry arm randomized 30 participants, with 31 analyzed in the acute phase and 31 analyzed in the chronic phase.

Wild lowbush blueberry supplementation was delivered orally as a beverage made with 22 g freeze-dried Vaccinium angustifolium powder mixed with 250 ml water. Participants received either a single acute dose at baseline or 41 sealed sachets to consume every morning for 6 weeks; each drink provided 1 cup or 150 g fresh-fruit equivalent, 121 mg anthocyanins, and 55 mg chlorogenic acid.

Blueberry supplementation showed a biphasic pattern: a single dose acutely improved positive affect at 2 hours and several executive function outcomes, but 6 weeks of daily supplementation did not improve depression, anxiety, stress, executive function, or serum biomarkers versus placebo. In the acute phase, positive affect improved versus placebo (p = 0.026), switch-trial accuracy improved (p = 0.025), and switch-trial reaction time was faster (p = 0.033); acute changes in positive affect correlated with executive function change in the blueberry group (r = 0.424, p = 0.017). After 6 weeks, depressive symptoms were not better with blueberry; BDI-II was 18.0 (SD 9.0) in the blueberry arm versus 14.9 in placebo, with p = 0.023 for the treatment effect, and no significant between-arm differences were seen for BDNF, hs-CRP, IL-6, SOD, or TBARS. Overall, the chronic supplementation phase was not beneficial and the authors concluded that blueberry may have transient acute effects without chronic antidepressant benefit in this sample.

The trial was small and limited to emerging adults from a single university community, which reduces generalizability. The chronic intervention was only 6 weeks, and several outcomes showed no treatment effect, so longer follow-up and replication are needed. Some reported acute and chronic findings were mixed, with only transient benefit and no clear biomarker response.