The Effects of Wild Blueberries on Depressive Symptoms in Young Adults: a Randomized, Double-blind, Placebo-controlled Trial
Phase: NA
Conditions: Depression, Anxiety, Anhedonia
Sponsor: University of Reading

 
 
 
Study Protocol and Statistical Analysis Plan 
Study title: The Effects of Wild Blueberries on Depressive Symptoms in Young Adults 
Acronym: BluMood 
Date: 07 April 2022 
 
 
 
 
 
 
 
 
 
 
 
 
 

1. Sample Size Calculation 
A mixed-design ANOVA carried out on data from a previous study in adolescents demonstrated a 
medium effect size (partial η2 = 0.04) of a four-week blueberry intervention on depressive 
symptoms (Fisk, Khalid, Reynolds, & Williams, 2020). An a priori power analysis in G*Power 
with this effect size indicated that a sample of 60 participants would be necessary to achieve a 
power level of 0.80 at a significance level of 0.05. 
2. Recruitment and Screening  
Participants will be recruited using opportunity sampling. The study will be advertised through 
email distribution and with posters across the University of Reading. Before interested participants 
are enrolled in the trial, we will invite them to the lab for a screening session to determine if they 
meet the eligibility criteria and give them an opportunity to become familiar with the cognitive 
task battery so as to reduce the influence of practice effects. Participants will be compensated with 
£120 ($156) for completing all phases of the study. 
3. Randomization and Blinding Process  
A researcher not involved in recruitment or data collection will use blocked randomization with 
random permuted blocks of two and four individuals to form the allocation list for the two 
comparison groups. The allocation sequence will be generated using the online randomization tool 
Sealed Envelope (v1.19.1) and will be concealed to the researchers enrolling and assessing 
participants. The interventions for chronic consumption will be distributed to participants in 
opaque, sealed sachets whereas on testing days the intervention drinks will be administered in 
opaque shaker bottles prepared by research personnel not involved in the conduct of the trial. Thus, 
both participants and investigators will be blinded to the treatment assignment throughout the 
study.  
4. Testing Protocol  
Visit 1 
09:00 – participants consume a standard breakfast of oat porridge after an overnight fast 
09:40 – participants complete cognitive task + PANAS-X  
10:00 – blood sample taken 

10:10 – participants consume the drink they have been allocated to (blueberry or placebo) 
11:10 – participants complete a battery of questionnaires (e.g. BDI-II, PHQ-9)  
11:25 – participants have their heart rate variability measured 
12:10 – participants complete cognitive task + PANAS-X 
12:25 – participants are given a bag with 41 sachets for the chronic phase of the study  
Visit 2 
09:00 – participants consume a standard breakfast of oat porridge after an overnight fast 
09:30 – participants complete a battery of questionnaires (e.g. BDI-II, PHQ-9)  
09:50 – participants have their heart rate variability measured 
10:00 – participants complete cognitive tasks + PANAS-X 
10:25 – blood sample taken 
5. Statistical Analysis Plan   
The outcomes will be analyzed using ANCOVAs adjusted for baseline values, sex, and habitual 
fruit and vegetable consumption as long as the assumptions for conducting the analysis are met. 
 
References 
Fisk, J., Khalid, S., Reynolds, S. A., & Williams, C. M. (2020). Effect of 4 weeks daily wild 
blueberry supplementation on symptoms of depression in adolescents. Br J Nutr, 1-8.