Gut-Brain link: prebiotics may improve sleep in poor sleepers

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Participants must self-assess themselves as being in good health. * Have a stable sleep/wake schedule (bedtime between 9pm and 1am and wake time between 6am and 10am at least 5 nights per week) * Aged 25 to 60 years at the time of randomisation * Fluent in English * Identify as a 'poor sleeper' as defined subjectively (i.e. poor sleep quality, unrefreshing sleep) and a total score of \>5 on the Pittsburgh Sleep Quality Index (PSQI). Exclusion Criteria: * Member of own household currently participating in this trial * Evidence of current or recent sleep disorders (e.g. sleep apnoea, insomnia, circadian rhythm disorders), taking any medication which exerts sedative effects, affects the CNS and/or sleep, or be currently unwell with any illness that affects sleep (i.e. disorders of the CNS). An initial screening for sleep disorders will be conducted using the Sleep Disorders Symptom Checklist-25 (SDS-CL; Klingman et al., 2017). If a participant reports positively to any of the 25 questions in terms of being affected for three nights per week, or more, this will be followed up using a clinical interview according to the International Classification of Sleep Disorders (ICSD-3) to exclude on the basis of a sleep disorder * History of seizures or epilepsy * Shift working or have a history of shift work within the previous six months * Currently, or within the previous 8 weeks, consuming any prebiotic or probiotic products/supplements (including specifically oligosaccharides) * Participation in any other intervention research trials * Sleeping at a location other than their usual residence more than two nights per week during participation * Travel across multiple time zones within the last three months or have planned travel across multiple time zones during the study * Current or recent mood disturbances or Axis I disorders * Current misuse of alcohol and/or drugs * Current smoker * Recent (within the last 12 weeks) infection and/or use of antibiotic medication * Pregnant, seeking to become pregnant or lactating * Those using (including within the last 2 weeks) proton-pump inhibitors * Milk allergy