Effects of Milk-based Drinks on Gut Microbiome, Sleep and Cardiometabolic Markers

Not Applicable

Recruiting

• Conditions: Sleep; Cardiovascular Diseases; Gut Microbiome; Cognitive Function and Mood; LDL Cholesterol

• Registration Number: NCT07071181
• Lead Sponsor: Sheffield Hallam University

Brief Summary

The purpose of this study is to evaluate the effects of kefir on gastrointestinal health, sleep quality, and biochemical parameters in adults who have sleep problems. Further measurements of cognitive function, arterial stiffness and blood pressure will also be assessed.

The following questions will be addressed during the study:

1. What effect does repeated ingestion of kefir have on the gut microbiome and can this positively influence sleep performance (quality and duration) in adults with sleep problems?

2. Does repeated ingestion of kefir impact LDL, triacyglycerols and non-HDLc in adults with sleep problems?

3. What effect does repeated ingestion of kefir have on cognitive function and mood?

4. What effect does repeated ingestion of kefir have on vascular function, inflammation and markers of immunity in adults with sleep problems?

In a randomised, crossover design study, participants will consume 250 ml of kefir (original flavour) or milk for 4 weeks with a 4-week washout.

Detailed Description

The gut microbiome is recognized as a key regulator of host health, influencing various physiological processes. Dysbiosis of the gut microbiome has been implicated in a range of adverse health outcomes, including disruptions in sleep architecture and impairments in cardiometabolic function. There is growing interest in identifying dietary interventions that can modulate gut microbiota composition and functionality. In particular, the consumption of fermented foods, such as kefir, has emerged as a potential strategy for promoting microbial homeostasis and improving health outcomes

This study conforms to a randomised, double-blind 2-arm crossover design. Participants will consume either Kefir (original flavour) or milk. Each arm will involve daily consumption of the drink for 4-weeks with a 4 week washout before crossing over to the opposite condition. Drinks will be administered in a counterbalanced order to minimise potential order effects.

The primary outcome of this study is a 5% change in LDL based on a previous study (Bellikci-Koyu et al., 2022).

Assuming type I error probability α = 0.05 and power of 80%, and effect size of 0.2 G\*power calculated that 32 participants would need to be recruited.

To account for potential drop out and balanced randomization, we will aim to recruit 40 participants.

Participants will be recruited through the use of posters around Sheffield Hallam University and the University of Leeds, through emails to staff and students, and contacts at surrounding universities. Potentially eligible participants will be identified through the use of a recruitment questionnaire before being invited to a screening visit for full consideration for the study. All participants will provide written informed consent before participating.

A linear mixed model analysis will be used to assess the effect of kefir on outcome parameters.

Study Timeline

• Status Verified: 2025-06
• Study First Submitted: 2025-07-09
• Study First Submitted QC: 2025-07-09
• Last Update Submitted: 2025-07-09
• Study First Posted: 2025-07-17
• Last Update Posted: 2025-07-17
• Study Start: 2025-08-01
• Primary Completion: 2026-03
• Study Completion: 2026-03-01

Recruitment & Eligibility

• Status: RECRUITING
• Sex: All
• Target Recruitment: 40

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

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: CROSSOVER

Primary Outcome Measures

Name	Time	Method
LDL Cholesterol	4-weeks	A blood sample via venepuncture will be taken at baseline and again after 4-weeks of daily consumption of the intervention or control for the assessment of LDL cholesterol. Blood samples will be obtained in a fasted state.
Gut microbiome	4-weeks	A stool sample will be collected from participants at baseline and after 4 weeks daily consumption of the intervention and control drink. The composition of the microbiome in stool will be measured by 16s rRNA sequencing.
Sleep quality and duration	4-weeks	Sleep quality and duration will be measured objectively and subjectively. For subjective measures, the Pittsburg Sleep Quality Index will be used to assess participant's sleep habits. The tool comprises of 7 sub-components and 18 items, including subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication and daytime dysfunction. In addition, the Epworth Sleepiness Scale. The Epworth sleepiness scale results range from 0 to 24.; Participants will also wear a Fitbit Charge 2 watch to track their sleep. Sleep measures will be obtained during the 7-day run in and final week of each study intervention for a total of 4 questionnaires to be completed by each participant and 4 week of objective sleep data.

Secondary Outcome Measures

Name	Time	Method
Blood samples	4-weeks	Serum or plasma samples will be obtained via venepuncture for the measurement of insulin, fasting blood glucose, lipids (LDL, HDL), triglycerides, iCAM, vCAM, CRP, and IL-6. All measurements will be taken in a fasted state at each intervention day.
Saliva IgG	4 week	Participants will be asked to provide a saliva sample after a 10 minute mouth rinse with water. Saliva samples will be analysed for IgA using ELISA.
Cognitive function	4 weeks	A cognitive test battery consisting of 3 cognitive tests will be used to investigate the effect of the intervention or control on cognitive function. Participants mood will also be assessed using the Positive and Negative Affect Schedule (PANAS) questionnaire that asks participants to rate a series of adjectives describing both positive and negative emotions.
Blood pressure	4 week	Blood pressure (systolic blood pressure, diastolic blood pressure and heart rate) will be measured in triplicate using a Vicorder after the paritipcant has rested for 15 minutes upon arrival to the lab. All measurements will be taken in a fasted state.
Pulse Wave Analysis	4 week	Carotid to femoral Pulse Wave Velocity (PWV) and Augmentation Index (Aix) will be measured using a Vicorder.

Trial Locations

Locations (2)

University of Leeds; 🇬🇧 Leeds, West Yorkshire, United Kingdom

College of Health, Wellbeing and Life Sciences; 🇬🇧 Sheffield, United Kingdom