Stress, Cortisol and Inflammation Simply Explained

1. What It Is About

Stress is the body's response to demands and threats. It is biologically programmed. The body switches to alarm mode and releases the hormone cortisol. Cortisol helps in the short term because it provides energy. If stress persists for a long time, the cortisol level often remains elevated.

Inflammation is the immune system's response to stimuli. This releases messenger substances that can be measured in the blood, for example CRP. Some of these substances are detectable only briefly, while others remain elevated for longer.

A bidirectional interaction between the two systems is under discussion: persistent stress can intensify inflammatory processes, and inflammation in turn can alter the body's stress response. This connection remains a hypothesis so far.

Stress can be measured in two ways: with questionnaires in which people describe how they feel, or via values in saliva, blood and hair. The cortisol level fluctuates strongly over the course of the day. This makes comparisons between measurements difficult.

2. What Studies Show

Programmes that reduce stress over several weeks are the best studied.

In a 2015 study, 144 employees who felt psychologically burdened took part. One group completed an eight-week mindfulness training. After the eight weeks, these participants felt less burdened and less stressed than the comparison group. The difference remained when the researchers accounted for age and other characteristics. However, the comparison group had no programme of its own, and the observation ended after eight weeks 7.

A 2020 study followed 60 people with a chronic inflammatory bowel disease over six months. In the group with the programme, two inflammation markers decreased, one in stool and one in blood. The cortisol level remained unchanged. The group was small, and there was no second group with another active programme 5.

A 2016 study examined 51 women with breast cancer. One group attended ten weekly group sessions on stress management; the other received only information. In the women with the sessions, inflammation-promoting genes were less strongly activated than in the comparison group. The research group linked this to longer disease-free survival observed after about eleven years. This was an analysis looking at possible associations 2.

A 2022 study tested sodium benzoate against a placebo without active ingredient and against the antidepressant sertraline in 117 people aged 55 and over with late-onset depression over eight weeks. Depression scores improved similarly in all three groups. Perceived stress decreased more strongly in the sodium benzoate group than in the placebo group 6.

A 2023 review summarises that stress management in cancer patients can reduce psychological burden and improve quality of life; individual studies also reported more favourable immune markers 1.

In a 2019 study with 115 healthy adults, all participants received a mild inflammatory stimulus. Those who had previously perceived more stress responded with stronger inflammation values 4.

3. What Remains Unclear

Many findings come from observational studies. Such studies show that two things occur together. They do not, however, indicate what the cause is. Whether persistent stress intensifies inflammation or whether inflammation alters stress perception is therefore often open.

The groups studied are frequently small. They often consist of specific occupational groups or patient groups. What applies to them need not apply to other people.

Studies lasting more than twelve months are still outstanding. Likewise outstanding are studies that jointly record perceived stress, cortisol and the activity of inflammation-relevant genes. Controlled human studies on the question of whether natural plant substances, for example polyphenols, influence stress values or inflammation values are also still outstanding.

A study in Zambia followed cash payments to households. Perceived stress did not decrease as a result. Only concern about food was associated with higher stress values 3.

4. What This Means in Everyday Life

A single cortisol value is difficult to interpret. The value fluctuates strongly over the course of the day and responds to sleep, eating, exercise and excitement. It gains informative value only together with several measurements and with the description of how burdened someone feels.

The studies on stress programmes in humans mentioned here examined mindfulness training, group sessions and group discussions. Such programmes run over weeks to months and are guided. Individual substances were usually not tested in these studies.

Wording helps with classification. Well proven means that several controlled human studies point in the same direction. For stress programmes there are indications, but these are not yet confirmed. For the connection between stress and inflammation the direction remains open.

The next points to clarify are long-term studies over more than one year and investigations that combine psychological and physical measurements.

All details with study numbers and sources: detailed page on Stress, Cortisol and Inflammation. For children: Stress, Cortisol and Inflammation for Children.