An interventional study of Original flavour kefir and Milk in Sleep, Cardiovascular Diseases and Gut Microbiome, sponsored by Sheffield Hallam University. Recruiting at 2 sites in United Kingdom. Open to participants aged 40 Years to 70 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-07-17.
Sponsored by Sheffield Hallam University · Not applicable, Interventional, and Other
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:
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.
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.
4,904 studies on the registry are indexed under Cardiovascular Diseases; 919 are open to participants now.
This study's planned enrollment of 40 is below the median of 100 across 2,738 interventional studies indexed under Cardiovascular Diseases.
Browse Cardiovascular Diseases studies →Sheffield Hallam University is the lead sponsor of 44 studies on the registry; 10 are open to participants now.
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Exclusion Criteria:
250ml of original kefir
Dietary Supplement: Original flavour kefir
250 ml of milk
Other: Milk
Participants will consume 250ml of original flavour kefir daily for 4 weeks. According to the manufacturer, "packed with billions of live cultures to support Gut health".
Participants will consume 250 ml milk daily for 4 weeks. This milk will not contain any live cultures.
LDL Cholesterol
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.
Time frame: 4-weeks
Gut microbiome
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.
Time frame: 4-weeks
Sleep quality and duration
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.
Time frame: 4-weeks
Blood samples
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.
Time frame: 4-weeks
Cognitive function
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.
Time frame: 4 weeks
Blood pressure
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.
Time frame: 4 week
Pulse Wave Analysis
Carotid to femoral Pulse Wave Velocity (PWV) and Augmentation Index (Aix) will be measured using a Vicorder.
Time frame: 4 week
Saliva IgG
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.
Time frame: 4 week
Small intestine bacteria composition
A subsample of participants will be instructed to ingest SIMBA capsules. Upon retrieval, the capsules will be analysed for the composition of microbiome in capsule fluid by 16s rRNA sequencing and the composition of metabolome in capsule fluid by NMR metabolomics. Capsules will be ingested at baseline and at 4-week time frame in each arm.
Time frame: From ingestion of capsules to their excretion
Dietary Patterns
During the course of the study, participants will be asked to maintain their normal dietary habits. Participants are asked to record their food and drink consumption for 4-days. This food record will be obtained 4-day prior to each intervention arm and 4-day prior to finishing each intervention arm.
Time frame: 4 days
Additional questionnaires
The Gastrointestinal Symptom questionnaire comprises 15 items in 5 sections: abdominal pain, reflux, indigestion, diarrhea and constipation. Questionnaire responses will be collected at baseline and after 4 week of ingestion of each study drink. In addition, a palatability questionnaire (Visual analogue scale) will be given to the participants at the end of each arm.
Time frame: 4-weeks
Body composition
Height and weight will be measured at each study visit for the purpose of BMI calculation. In addition Bioelectrical impedance analysis (BIA) will be used to measure fat-free mass, total body water, percent fat, body cell mass, intracellular water, and extracellular water.
Time frame: 4 week
Plan to share: No
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Sheffield Hallam University