f chronic stress or illness. When HPA-axis dysfunction occurs, the production and rhythmic timing of cortisol and other stress-related hormones becomes disrupted. This is believed to play a central role in causing mood disorders and cognitive problems.
A third way psychobiotics are hypothesized to act on the brain is through their anti-inflammatory actions. Chronically elevated levels of inflammation throughout the body and brain are now known to be one of the major underlying causes of depression and other mood and cognitive disorders. This inflammation can stem from the gut, and some psychobiotics may have their effects in the brain by lowering inflammation.
Which Probiotics Are Psychobiotics?
Research is beginning to identify which probiotics have mild-altering effects and what those effects are. In studies in healthy people, different psychobiotics have been shown to boost mood and cognitive function and decrease stress and anxiety-like symptoms.
Certain psychobiotics have also been shown to treat depression, anxiety, and other mental health and cognitive issues in patients with psychological disorders and/or other medical conditions.
Psychobiotics for Depression and Anxiety
A clinical trial randomly assigned patients with major depressive disorder to receive either probiotic supplements or placebo for eight weeks. The probiotic pills consisted of Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum (2 billion CFUs each).
After eight weeks, patients who received the probiotic had significantly decreased total scores on the Beck Depression Inventory, a widely used test to measure the severity of depression, compared with placebo. In addition, they had significant decreases in systemic inflammation as measured by hs-CRP, significantly lower insulin levels, reduced insulin resistance, and a significant rise in glutathione, the body’s master antioxidant.
Other psychobiotics have beneficial consequences on mood and anxiety-like symptoms in people without depressive or anxiety disorders.
In a study to investigate the possible effects on anxiety, depression, stress, and coping strategies in healthy human volunteers, a probiotic containing Lactobacillus helveticus R0052 and Bifidobacterium longum R0175 (Probio’Stick®) alleviated psychological distress, particularly depression, anger-hostility, and anxiety, and improved problem solving when taken for 30 days. The researchers concluded that L. helveticus R0052 and B. longum R0175 have beneficial psychological effects in healthy humans.
Psychobiotics can also help boost mood and ease anxiety in people suffering from various chronic diseases. The same probiotic studied above (Lactobacillus casei strain Shirota) was used in another double-blind, placebo-controlled trial in patients with chronic fatigue syndrome.
Patients were randomized patients to receive either 24 billion colony forming units of Lactobacillus casei strain Shirota or a placebo daily for two months. The people taking the probiotic had a significant decrease in anxiety symptoms.
Many additional psychobiotics have been shown to treat depression and anxiety in animal studies. Lactobacillus plantarum strain PS128, for example, is known to increase dopamine and serotonin and decrease depression-like behaviors in mice. In depressed mice that have been subjected to early-life stress, this same psychobiotic decreases cortisol, normalizes the stress response system (the HPA axis), and decreases depression.
Both Bifidobacterium longum 1714 and Bifidobacterium breve 1205 reduce anxiety-like behavior and improve performance on cognitive tests in anxious mice.[12,13]
Psychobiotics for Stress
Psychobiotics have also been shown to help people and animals undergoing stress. A fermented milk drink (kefir) that contained Lactobacillus casei strain Shirota prevented stress-related cortisol increases and raised serotonin levels in stressed medical students. Moreover, the probiotic drink decreased stress-related physical symptoms such as abdominal pain and cold symptoms.
The study authors concluded that taking 