Do probiotics help stress hormones?

In recent years, there has been growing interest in the potential for probiotics to help regulate stress hormones. Probiotics are beneficial bacteria that can be found in certain foods or supplements. Many studies have suggested that probiotics may help improve gut health, immune function, and mental health. With stress being a major factor impacting health, researchers have begun exploring if probiotics can also influence stress hormones and our response to stress.

What are probiotics?

Probiotics are live microorganisms, typically bacteria, that are believed to provide health benefits when consumed. The most common strains found in probiotic supplements and foods include:

  • Lactobacillus
  • Bifidobacterium
  • Saccharomyces
  • Streptococcus
  • Bacillus

Some benefits associated with probiotics include:

  • Supporting gut and microbiome health
  • Boosting immune function
  • Aiding digestion and nutrient absorption
  • Alleviating diarrhea and other GI issues
  • Relieving symptoms of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD)

Probiotics can be found in fermented foods like yogurt, kefir, sauerkraut, and kimchi. They are also available as dietary supplements in capsule, powder, or liquid form. When choosing a probiotic, it’s important to select one that contains live and active strains that are able to survive the journey through the digestive system.

What are stress hormones?

When we encounter a threat or challenge, our body activates a physiological stress response. This involves the release of stress hormones like cortisol, adrenaline (epinephrine), and norepinephrine. These hormones trigger a cascade of effects to prepare the body to deal with the stressor by either fighting, fleeing, or freezing:

  • Increased heart rate, blood pressure, breathing rate
  • Heightened brain activity and alertness
  • Slowed digestion
  • Increased blood sugar for energy
  • Inhibition of growth, reproduction, immunity temporarily

This stress response is extremely adaptive in the short-term for helping us manage immediate threats. However, when stress is chronic and the stress response persists, it can start impacting health. Prolonged high levels of stress hormones have been associated with:

  • Anxiety and depression
  • Headaches and migraines
  • High blood pressure
  • Lowered immunity
  • Insomnia
  • IBS and digestive issues
  • Weight gain

Given the wide-ranging effects of stress hormones, finding ways to manage them and achieve hormonal balance is important for overall health.

How could probiotics help with stress hormones?

Researchers are actively investigating whether probiotic supplementation may modulate levels of stress hormones and our physiological response to stressors. Several mechanisms have been proposed for how probiotics may influence stress hormones and stress responsiveness:

  • Gut-brain axis: There is constant communication between the gut and the brain via the vagus nerve, hormones, and cytokines. Probiotics may improve gut health and microbial balance, which in turn benefits brain function and stress pathways.
  • Anti-inflammatory effects: Probiotics can reduce inflammation, which may lower circulating stress hormones like cortisol.
  • Production of neurotransmitters: Certain probiotic strains may increase production of mood-regulating neurotransmitters like GABA, serotonin, and acetylcholine.
  • Regulating HPA axis: Probiotics may help regulate the HPA axis, the central stress response system involving the hypothalamus, pituitary gland, and adrenal glands.

Animal studies on probiotics and stress

A number of animal studies have provided evidence that probiotic supplementation can influence hormonal responses to stress.

In a study on rats, taking Lactobacillus farciminis for 2 weeks attenuated the stress-induced increase in corticosterone levels compared to controls. Rats receiving a probiotic mix of Lactobacillus helveticus and Bifidobacterium longum had lower cortisol levels following a stressful water maze test.

Another rat study found that supplementation with Bifidobacterium infantis helped regulate tryptophan metabolism by the gut microbiota after a forced swim test. Tryptophan is a precursor of serotonin, an important neurotransmitter involved in mood regulation.

Mice subjected to restraint stress had an exaggerated stress reaction if they lacked gut bacteria compared to mice with normal intestinal flora. When the germ-free mice were given a probiotic strain called B. infantis, their hormonal stress response was reduced.

Overall, these animal studies provide preliminary evidence that probiotic supplementation can attenuate hormonal responses to stressors.

Human studies on probiotics and stress

While animal studies may look promising, do probiotic effects on stress response and hormones translate to humans? Several clinical studies have attempted to investigate this:

In a controlled study of healthy medical students, drinking probiotic yogurt containing Lactobacillus casei strain Shirota 3 times a day resulted in lower cortisol levels in response to examination stress compared to students who drank plain yogurt.

A small study in healthy petrochemical workers showed that taking a probiotic capsule with 8 strains of bacteria for 6 weeks helped buffer the cortisol response to acute stress exposure.

In men with high stress levels, consumption of probiotic yogurt containing L. casei strain Shirota daily for 8 weeks was found to have anti-anxiety and mood-lifting effects compared to placebo yogurt. This was associated with changes in brain activity thought to be related to emotional and stress processing.

However, not all human studies on probiotics have shown benefit. For example, a study in chronically stressed women taking B. longum for 6 weeks failed to find significant differences in cortisol levels compared to placebo.

More high quality, large clinical trials in humans are still needed to clarify the effects of specific probiotic strains on stress hormone levels and stress responsiveness.

Key considerations

When considering the potential stress-relieving effects of probiotics, keep the following key points in mind:

  • Benefits are likely to be strain-specific, with certain probiotic strains being more effective than others for stress.
  • Improvements may be more evident in those experiencing chronic stress or with disrupted gut microbiota.
  • Supplementation for longer durations (minimally 6-8 weeks) may be needed to observe effects.
  • Probiotics are just one component of coping with stress and should be combined with lifestyle approaches like mindfulness, exercise, sleep, and a healthy diet.

Mechanisms of action

Researchers are actively investigating the biological mechanisms behind the stress-regulating effects of probiotics. Some key mechanisms include:

  • Influencing brain regions involved in stress response: Imaging studies in humans have shown that probiotics can impact activity in areas like the hypothalamus, prefrontal cortex, and limbic regions that regulate mood, emotion, stress responses and behavior.
  • Increasing neurotransmitter production: Probiotics may increase plasma levels of neurotransmitters like serotonin, GABA, and acetylcholine that are involved in regulating stress pathways.
  • Altering gut microbiota: Probiotics can favorably influence gut microbiota composition, which in turn benefits gut-brain axis communication and downregulation of inflammatory pathways.
  • Regulating HPA axis: Probiotics may restore balance in the HPA axis, reducing hyperactivity that contributes to high cortisol and dysregulated stress reactivity.

Effects on other biomarkers

In addition to directly lowering stress hormone levels, probiotic supplementation has been associated with beneficial changes in other biomarkers related to the stress response:

  • Inflammatory markers: Probiotics can reduce inflammatory cytokines and increase anti-inflammatory cytokines to improve stress-associated inflammation.
  • Oxidative stress markers: Probiotics can mitigate oxidative damage and increase antioxidant levels that tend to be disrupted by stressors.
  • Serotonin: Probiotics have been shown to increase plasma serotonin levels, which may contribute to the mood-lifting effects.
  • Nitric oxide: Higher nitric oxide levels may be one mechanism behind the anti-anxiety effects of probiotics observed in some studies.
  • Brain-derived neurotrophic factor (BDNF): This protein involved in nerve growth and brain plasticity has been increased with probiotics, leading to positive effects on mood and cognition.

Limitations and future directions

Despite promising findings on probiotics for stress response, there are some limitations to consider:

  • Small sample sizes in human studies
  • Lack of consensus on optimal strains, dosages, and duration
  • Need for larger RCTs with standardized methodology
  • Challenges of variability in microbiome composition between individuals
  • Mechanisms not fully elucidated

Future research is warranted with larger clinical trials, comparison of probiotic strains and combinations, exploration of long-term effects, and more studies clarifying the mechanisms of action.


Preliminary evidence indicates that supplementation with specific probiotic strains may help manage stress hormone levels and reactivity to stressors. This effect is thought to be mediated largely through the gut-brain axis and interactions between gut microbiota and stress response pathways. However, larger scale clinical studies and further mechanistic data in humans are still needed.

Probiotic supplementation appears to be a generally safe and potentially promising option as an adjunct to a healthy lifestyle and stress management. But more rigorous placebo-controlled trials are required to substantiate benefits for stress hormones specifically before any strong conclusions can be made.

The gut microbiome is complex, and responses are likely highly individual. Those experiencing chronic stress, anxiety, depression, and poor digestive health may derive the most pronounced benefits from adding probiotic foods and supplements to support a healthy microbiome-gut-brain axis interaction.

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