A new study from Denmark shows that gut symptoms are widespread – even among people that seem very healthy. The findings challenge the idea that such symptoms always signal disease and may lead to clearer guidelines on when they require attention.
Susanne, 32 years old, lives a healthy and active life. Nevertheless, she struggles with bloating and constipation, which makes her stomach feel heavy and uncomfortable. She has seen doctors several times, had blood tests and stool samples – all normal. Nevertheless, she cannot shake the worry: what if something serious lurks behind her discomfort? A tumour hidden in her intestine? The thought gnaws at her day after day.
Young people like Susanne can probably take it easy. The new study published in BMJ Open Gastroenterology shows that symptoms like hers are widespread – even among people who are completely healthy. The study, based on questionnaires from healthy blood donors, was carried out by researchers at the Department of Clinical Medicine of Aarhus University, Denmark.
Christian Erikstrup and first author Anne Karmisholt Grosen led the study. It is the world’s largest study of its kind and stands out for using blood donors as a reference group – a method that could inspire similar research elsewhere.
“I am surprised by how many healthy people report gut symptoms. Not just a few ones, but often several at once – in a group we normally consider extremely healthy. It shows how wide the normal range really is,” says Anne Karmisholt Grosen.
“This challenges the perception that gut symptoms are always a sign of illness,” adds Christian Erikstrup.
Almost half of women younger than 50 years reported three or more symptoms at the same time – often bloating, pain and changes in bowel habits. This calls for awareness that not all symptoms from the gut are signs of disease – both in medical practice and in research.
What we can learn about the gut from healthy blood donors
The purpose of the study was to determine how common various gastrointestinal symptoms are among healthy adults. To do this as accurately as possible, the researchers used blood donors as their data source. Blood donors are a well-screened, healthy group, regularly monitored with health checks and blood tests over many years.
Donating blood requires meeting several health criteria and declaring yourself free of disease. This makes the group particularly suitable as a benchmark for normality.
Between 2020 and 2023, more than 53,000 blood donors completed questionnaires about 13 gastrointestinal symptoms – from bloating and constipation to diarrhoea and stomach pain. The questionnaire was pilot tested and the answers were grouped into a distinct symptom profile.
When to take stomach problems seriously
The responses were collected over 2.5 years to capture seasonal variation and linked to the blood bank’s existing health data. This gave the researchers unique insight into both short-term variation and long-term patterns in one of the healthiest population groups.
The data collection was carried out as part of the Danish Blood Donor Study – a large, nationwide research platform in which researchers, with the consent of the donor group, can investigate many phenomena including the body’s resistance to infections and mental well-being.
In this case, the data were used to analyse how the symptoms were distributed in a group that is otherwise considered healthy. The researchers developed a scoring system that gave each participant a total symptom score depending on how many symptoms they reported.
“This helps us to understand which symptoms are so common among healthy people that they should not inherently cause concern – and which ones should continue to set off alarm bells,” says Christian Erikstrup.
When gut problems matter – and when they do not
The researchers have not redrawn the line between sick and normal but emphasise that their results should guide that work. The data can thus form a new basis for future guidelines that take greater account of which symptoms are actually common in the healthy part of the population.
This matters, for instance, in faeces transplantation – in which stools from healthy donors are used to restore gut balance among people with severe diarrhoea caused by specific bacteria.
The donor being healthy is crucial for patient safety. The aim is to avoid inadvertently transferring infections or the risk of infection from the donor to the recipient, who may already be weakened. That is why blood donors, already screened for good health, are often asked if they would also donate faeces when they come to donate blood.
Mild discomfort should not be a barrier for donors
This practical principle has previously been described in a 2019 study in which the same research group in Denmark analysed the entire process of faecal donation and the establishment of a faecal bank. It emphasised the importance of safe and thoroughly screened donors – but also that an overly rigid focus on the absence of all conceivable symptoms risks unnecessarily limiting the donor pool. This concern contributed to Christian Erikstrup and his colleagues launching the new study.
“We show that many blood donors have mild gastrointestinal symptoms. And that raises the question of whether excluding them as faeces donors is reasonable,” says Christian Erikstrup. He warns that healthy, eligible donors could be excluded unnecessarily because of mild symptoms.
The current guidelines, published by the European Fecal Microbiota Transplant Group, recommend that faeces donors should be symptom-free. But this is probably too rigid a way of thinking, which, paradoxically, could put recipients at risk, warns Erikstrup, who nevertheless agrees in principle that efforts should be made to protect the recipients.
“The new data enable us to reassess which symptoms are actually relevant to patient safety and which should be accepted as normal,” he says.
Antibiotics can tip the balance in the gut
The researchers are already linking the questionnaire responses to national health registries to find patterns in which symptom profiles, if any symptoms are present, can predict later illness. The goal is to be able to distinguish harmless symptoms from those that could potentially lead to illness.
This builds on previous experience from faeces transplantation, which has shown that the donor’s health status can affect the outcome of the treatment. This applies, for example, to antibiotics, which can disrupt the balance of the gut’s bacterial flora and temporarily weaken the effect of faeces transplantation. Faeces transplants are less effective if the donor has taken antibiotics within the previous year.
It is therefore important to know which factors actually impair the donor’s suitability – and which symptoms or conditions have no bearing on patient safety. This is precisely the knowledge that researchers hope to obtain by combining questionnaire data with registry information. This will help to avoid rejecting healthy donors for no reason and ensure that patients receive optimal treatment.
New knowledge helps both doctors and patients
The new data can also make a difference in medical practice. Christian Lodberg Hvas, Clinical Professor of Gastroenterology at Aarhus University and Senior Physician at Aarhus University Hospital, is part of the research team and is responsible for patient treatment. He emphasises that the results provide a much more nuanced picture of what is normal.
The results can help doctors distinguish between harmless symptoms and those that require further investigation. It could spare patients needless worry – and reduce referrals for unnecessary examinations. The study’s significance therefore extends beyond the world of research. It can be used to refine doctors’ assessments of patients and reduce unnecessary worry.
For Susanne – and thousands of other people – the study brings peace of mind. Even the healthiest people in Denmark rarely have trouble-free stomachs. Discomfort is not always disease – and is sometimes simply part of life.
On a final note, Anne Karmisholt Grosen says that if you are older than 40 years and experience a new change in your bowel habits, you should always consult your doctor for a colonoscopy.
