Effects of Milk-based Drinks on Gut Microbiome, Sleep and Cardiometabolic Markers
This study aims to understand if drinking kefir, a fermented milk drink, can improve sleep quality and duration in adults aged 40 to 70 who experience sleep problems. Researchers also want to see how kefir affects important health markers such as gut bacteria (the 'gut microbiome'), levels of 'bad' cholesterol (LDL), and overall heart health. Additionally, the study will look at changes in mood and thinking skills. Participants will drink either kefir or regular milk daily for four weeks, with a break before switching to the other drink, so we can compare the effects of both.
At a glance
What is this study about?
You know how important a good night's sleep is, and maybe you've heard that what you eat can affect your gut and even your mood. This study is all about exploring the connection between a special fermented milk drink called kefir, your gut health, your sleep, and some important markers for your heart health.
Our bodies are home to trillions of tiny bacteria, often called the 'gut microbiome.' These bacteria play a huge role in many parts of our health, including how well we sleep and even our risk of heart problems. Researchers are increasingly interested in whether certain foods, especially fermented ones like kefir, can help keep these gut bacteria balanced and lead to health benefits.
We're specifically trying to find out if regularly drinking kefir can improve the quality and length of sleep for people who struggle with it. We'll also be looking closely at whether kefir can help reduce 'bad' cholesterol (LDL), affect your mood and thinking skills, and even improve markers related to your heart and immune system. By comparing kefir to regular milk, we hope to get a clear picture of its potential benefits.
Key takeaways
- This study explores the health effects of kefir.
- It focuses on sleep, gut health, and heart health markers.
- Participants will drink either kefir or milk daily for two 4-week periods.
- The study includes adults aged 40-70 with sleep difficulties.
- There are four in-person visits to the lab.
- It aims to understand if kefir can improve health in a simple, dietary way.
Who may be eligible?
This study is looking for volunteers between the ages of 40 and 70 years old. An important part of joining is that you should be someone who experiences problems with sleep, which will be checked using a special questionnaire. We also need people whose weight falls within a certain range (specifically, your BMI should be between 25 and 35 kg/m2).
If you're a woman, you can still take part if you're using contraception or hormone replacement therapy (HRT), as long as your treatment hasn't changed in the last three months. You should also be happy to drink either kefir or milk every day for four weeks during the study periods and attend our lab for visits.
However, you won't be able to join if you're allergic or intolerant to milk products, if you're pregnant or breastfeeding, or if you have any existing gut problems. We also need you to have a good understanding of English to complete the questionnaires and tests, and be able to travel to our lab for appointments.
Could this study suit you?
Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.
- Are you between 40 and 70 years old?
- Do you often have trouble sleeping?
- Are you comfortable drinking milk-based products daily?
- Can you travel to the universities in Sheffield or Leeds for appointments?
- Do you understand English well enough to complete questionnaires?
What does participation involve?
If you decide to take part, you'll first be asked to fill out a questionnaire to see if you meet the study's requirements. If you seem suitable, you'll then come in for a screening visit where we'll explain everything in detail and ask for your consent to participate.
The study involves two main periods of four weeks each. In one period, you'll drink 250ml of original flavour kefir every day. In the other period, you'll drink 250ml of regular milk every day. There will be a four-week break, called a 'washout' period, between these two drinking phases. We'll tell you which drink to start with.
Throughout the study, you'll need to visit our lab on four separate occasions. During these visits, we'll collect various measurements, which might include blood tests, checks of your heart health, and tests for your sleep quality, mood, and thinking skills. The total duration of your involvement, including the washout period, will be around 12 weeks.
Potential risks and benefits
Locations (2)
- University of LeedsVerified postcodeLeeds, United Kingdom· Not yet recruiting
- College of Health, Wellbeing and Life SciencesVerified postcodeSheffield, United Kingdom· Recruiting
Common questions
What is kefir?
Kefir is a fermented milk drink, a bit like a thin yogurt, but made with kefir 'grains' which are a mix of bacteria and yeasts.
Will I know if I'm drinking kefir or milk?
No, this is a 'double-blind' study, meaning neither you nor the researchers will know which drink you are having at any given time until after the study is over.
How much drink will I have to consume daily?
You will need to drink 250ml (about half a pint) of either kefir or milk every day during the study periods.
What kind of sleep problems is the study looking for?
The study is looking for people who generally have poor sleep quality, which will be assessed using a specific questionnaire called the Pittsburgh Sleep Quality Index.
Where will the study visits take place?
The study visits will take place at Sheffield Hallam University or the University of Leeds.
How to find out more
Tony Lynn,, PhD
Always speak to your GP or specialist before deciding to take part in a study.
Interested in taking part?
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