Who are study participants?
Study participants, in German often called Probanden, are people who volunteer to take part in a scientific study, usually healthy individuals. If participants have the condition under study, they are typically called patients. "Human study" covers both groups.
Study participants explained simply
Study participants (also called subjects or volunteers) are people who take part in an investigation of their own free will so that researchers can learn something about the body or the effect of a substance. In the narrower sense, subjects are healthy, while patients have the condition being studied. In everyday speech the terms get mixed, and a trial in people is often just called a human study.
Before taking part, people receive information and give written informed consent. Ethics committees review in advance whether the study is justifiable.
Why the distinction matters
Whether a study involved healthy subjects or patients determines what it can show:
- Healthy subjects are well suited to questions about how a substance is absorbed and distributed, such as pharmacokinetics and bioavailability. The groups are uniform, with few confounding factors.
- Patients are needed to test whether the symptoms of a condition change.
A result in twelve healthy subjects cannot simply be transferred to people with a disease. Conversely, a study in patients does not automatically show how much of a substance actually reaches the blood.
From cell to human
How study levels differ in their transferability to humans.
| Level | What is studied | Transferability to humans |
|---|---|---|
| Level In vitro | What is studied Cells in the lab | Transferability to humans Low |
| Level Animal study | What is studied Animals, e.g. mice or rats | Transferability to humans Limited |
| Level Healthy subjects | What is studied Mostly healthy people | Transferability to humans High for absorption and tolerability |
| Level Patients | What is studied People with the condition | Transferability to humans High for symptoms and disease course |
Examples from the curcumin field
The well-known piperine study by Shoba and colleagues (1998) gave subjects 2 grams of curcumin, once without and once with 20 mg of piperine, and measured blood levels. That is a question of absorption, suited to a small number of subjects. Such a study says nothing about joint complaints. Conversely, the osteoarthritis question needs studies in people with osteoarthritis. When reading studies, always check the number of participants, the participant group and the duration.
How does a study with subjects proceed?
First an ethics committee reviews the study concept. Then subjects are selected by defined criteria, such as age, health status and medication use. After being informed they sign a consent form and can withdraw at any time without disadvantage. In absorption studies they receive the test substance and blood samples are taken over several hours. From the measurements researchers calculate, for example, the area under the curve (AUC).
Frequently asked questions
How many subjects does a study need?
That depends on the question. Absorption studies often manage with a small group when each person tests several variants one after another (crossover). For effects on symptoms, considerably more participants are usually needed.
Are subjects paid?
They often receive compensation for their time and effort. It must be designed so that it does not pressure people into taking part.
The number of participants matters: in very small groups, chance fluctuations can mimic large effects. A clear message usually emerges only when several independent studies show the same thing.
