The design follows a randomised, double blind, placebo controlled cross over design. Participants will be recruited via social media, posters in the local area, and through word of mouth and email advertisements and will be invited to take part in an in-person study investigating a fruit drink on mood and cognition. Participants will come to the Nutrition-cognition lab at the Psychology department for a screening session, during the session the study will be explained by the researcher and the participant will receive the participant information sheet. If the participant is eligible and wants to take part, they will sign the consent form. Data collected at screening will include age, ethnicity, highest level of education, marital status, specific diet, income, employment, physical illnesses, psychological diagnosis, regular medications, how old their infant is, infant gender, previous children, and age of other children as well as postnatal depression, postnatal anxiety (mother's sample only), state anxiety (father's sample only) a food frequency questionnaire and anthropometric measures to determine body mass index (BMI). Participants will then complete practice versions of the cognitive tests. Office for National Statistics recommendations will be used when collecting participants demographic details of ethnicity and income.

A week later, upon arrival at the Nutrition Cognition Lab (approximately 9am) participants will be asked to note what they had for breakfast (to ensure they have the same breakfast next week for standardisation) and a researcher will ask whether they have followed the pre-session restrictions prior to coming in for the visit (see below). Participants will then complete the mood and cognitive questionnaires (listed below) and have their blood pressure taken (duration 30 min). The order of questionnaires and cognitive tasks will be kept the same throughout the study. Participants will then be randomly allocated to consume one of two interventions (blueberry drink or a similarly flavoured placebo drink). The blueberry drink consists of 46g freeze dried wild blueberry powder mixed with 250ml water, the placebo drink contains 46g placebo powder matched for sugars and vitamin C content of the blueberry powder, mixed with 250ml water. The tests will then be repeated 2 hours after consuming the drink. Participants will be able to leave the lab and have free time for the 2hrs in between testing. During the procedure, we will also request that if participants bring their infant on the day, that they also bring a partner (friend, relative or parent of infant) to care for their infant during this time so to not distract the participant during the mood and cognitive tasks. Participants will then return to the lab a week later and carry out the same procedure, though consuming the other intervention drink. After the study has been completed, participants will be debriefed and given the opportunity to ask any questions. Participants will also be reminded of their right to withdraw their data from the study if they wish. Helplines and support web links will be provided to all participants as well as encouragement for participants to contact their GP should they wish to seek support. Helplines and weblinks include Samaritans UK and PANDAS Foundation. Weblinks to NHS, MIND and the Association for Postnatal Illness.

Pre-session restrictions: Twenty-four hours before the first and second test sessions, all participants will be advised to follow a low flavonoid diet which will be advised by an information sheet provided by the researchers upon sign-up. These restrictions will be implemented as a control measure so that other dietary flavonoids do not interfere with the results of the study and researchers will check adherence to restrictions prior to the first sitting of the study. Within this 24-hour period, participants will also be asked not to drink alcohol, caffeine or take recreational drugs. Participants will also be asked to refrain from exercise and food 2 hours before and following the intervention (water will be allowed) to avoid confounding effects.