Kefir versus milk for gut microbiome, sleep, and cardiometabolic markers
Official title: A Randomised, Double-blind Trial to Measure the Effects of Milk-based Drinks on Gut Microbiome, Sleep, and Cardiometabolic Markers in Adults With Poor Sleep
Run by Sheffield Hallam University · NCT07071181 · Data updated 2026-11-12
This project will test whether drinking 250 ml of kefir daily for 4 weeks, compared with milk, can improve gut bacteria, sleep quality, and LDL cholesterol in adults aged 40–70 with poor sleep and BMI 25–35.
Quick facts
| Study type | Interventional |
|---|---|
| Ages | 40 Years to 70 Years |
| Sex | All |
| Enrollment | 40 (estimated) |
| Sponsor | Sheffield Hallam University Academic / other |
| Locations | 2 sites (Leeds, West Yorkshire and 1 other locations) |
| Status | Recruiting |
| Started | August 2025 |
| Main results expected | March 2026 |
| Study ends | March 2026 |
| Registry record updated | July 17, 2025 |
| Trial ID | NCT07071181 on ClinicalTrials.gov |
Is this trial a fit for you?
✓Likely a good fit
Ideal candidates are adults aged 40–70 with poor sleep (PSQI >5), BMI 25–35 kg/m2, no milk allergy, and ability to drink the test beverages daily and attend four laboratory visits.
✕Probably not a fit
People who are allergic or intolerant to milk, pregnant or breastfeeding, have gastrointestinal disorders, or are outside the age or BMI range are unlikely to benefit from this protocol.
A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.
What this trial studies
In a randomised, double-blind, two-arm crossover design, 40 adults with poor sleep and BMI 25–35 will consume 250 ml of kefir or milk daily for 4 weeks followed by a 4-week washout before crossing over. The primary outcome is a 5% change in LDL cholesterol and secondary outcomes include gut microbiome composition, sleep quality and duration, cognitive function and mood, arterial stiffness, blood pressure, triglycerides, non-HDL cholesterol, inflammation, and immune markers. Stool, blood, and sleep measures will be collected at baseline and at the end of each intervention period, and drinks will be administered in counterbalanced order to minimise order effects. The trial was powered at 80% to detect small effects and aims to recruit 40 participants to allow for dropouts.
Why it matters
Potential benefit: If successful, regular kefir consumption could modestly improve sleep and lower LDL and other cardiometabolic risk markers through beneficial changes in the gut microbiome.
How similar studies have gone: Small prior studies of kefir and other fermented foods have reported modest changes in gut microbiota and some lipid improvements, but results are limited and not yet conclusive.
Who can join: the full rules
Show full inclusion / exclusion criteria
Inclusion Criteria: * Aged 40-70 years old * Suffer with poor sleep (measured using the PIttsburg Sleep Quality Index with a score \> 5) * BMI in range of 25-35 kg/m2 * Willingness to consume each study drink daily for 4 weeks and attend the laboratory on 4 separate occasions * For women: Medication in the form of contraception or HRT providing these have not been modified 3 months prior to the first study day Exclusion Criteria: * Intolerance or allergy to milk-based products * Pregnancy/breastfeeding * Insufficient English language skills to complete all study questionnaires and perform the cognitive tests * Gastrointestinal disorders * Inability to attend the laboratory due to travel/mobility difficulties
Where it's running
-
College of Health, Wellbeing and Life Sciences
Sheffield, United Kingdom Recruiting -
University of Leeds
Leeds, West Yorkshire, United Kingdom Not yet recruiting
Study contacts
- Principal investigator: Tony Lynn, PhD — Sheffield Hallam University
- Study coordinator: Tony Lynn,, PhD
- Email: T.lynn@shu.ac.uk
- Phone: 0114 2252065
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How to take part
- Review the eligibility criteria above with your treating physician.
- Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
- Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.