Probiotics are beneficial microbes that promote digestive health. This effect, in turn, strengthens a strong connection that many experts believe exists between your gut and your brain, called the gut-brain axis (GBA). The idea is that the microorganisms in your gut have many functions, such as:
- Balancing neurotransmitters that may affect sleep habits, appetite, or mood
- Reducing inflammation that could play a part in depression
- Influencing brain function and your stress response
- Fermenting fiber to generate nutrients for the cells lining the intestines
The GBA enables the conversation between your central nervous system (CNS) – your brain and spine, controlling your thoughts and emotions – and your enteric nervous system (ENS) – all the nerve cells lining the walls of your digestive organs. Experts say there are more neurons in your gut than in your entire spinal cord, and the ENS has even been nicknamed the "second brain".
The GBA is still a new area of research, and we don’t yet understand exactly how probiotics affect mental health. But, while we don't yet know the precise mechanics of how it works, many clinical studies show a positive correlation between certain probiotics and mental health benefits. Keep reading to learn about the potential that balancing your gut microbiome with probiotics may have.
How Does Gut Health Relate to Chronic Physical & Mental Conditions?
We don't fully know what causes anxiety, but some evidence suggests that there is a connection between anxiety and gut health. A survey of studies that explored the relationship between anxiety and fecal microbiota transplantation (FMT) – transplanting a sample of the gut microbiome of someone who doesn't have anxiety into the gut of someone who does – concluded that FMT has highly effective outcomes and only a few possible complications.
Research suggests that certain fungal overgrowths within the body can be a biomarker of asthma risk. Antibiotics that reduce the relative abundance of Lactobacillus bacteria are generally associated with this kind of overgrowth. As a result, researchers have been exploring the usefulness of lactic acid-producing bacteria, as in a recent study of the anti-allergic effects of Lactobacillus plantarum K37. The probiotic seemed to suppress allergic reactions like airway inflammation, a common asthma symptom.
Generalized Anxiety Disorder (GAD)
A study of people with GAD found that they had less microbial diversity in their gut; specifically, lower abundances of Firmicutes and Tenericutes. The presence of certain bacteria also correlated with anxiety severity, while others correlated with reduced anxiety. Balancing these bacteria could help reduce the effect of GAD.
Attention-Deficit Hyperactivity Disorder (ADHD)
A clinical trial of boys around the ages of 12 and 13 found significantly less gut microbial diversity in those with ADHD, along with a negative correlation between hyperactivity and gut diversity.
People who have autoimmune conditions like rheumatoid arthritis often show reduced gut microbial diversity, correlating with longer disease duration. Using probiotics to restore the intestinal barrier and balance the gut microbiome in the period before clinical arthritis might help delay the onset and lessen the severity of rheumatoid arthritis.
Can Probiotics Correct Gut Dysbiosis from Chronic Conditions?
Though many chronic conditions do relate to a high prevalence of gut dysbiosis, it's important to note that finding this trend is just the first step. Much more research is necessary to identify a specific probiotic strain or combination of strains that might correct both the dysbiosis and the co-occurring condition.
For instance, while evidence shows Lactobacillus rhamnosus GG has no effect on Crohn's disease, a study on a different strain may produce better results. As research on the effects of different probiotic strains continues to show positive signs, there will be further exploration into the potential these supplements may have.
Studies of Probiotics for Anxiety & Depression
Depression and anxiety are related to an imbalance of different neurotransmitters, like serotonin, dopamine, and gamma-aminobutyric acid (GABA). A significant amount of these neurotransmitters come from the ENS. As a result, probiotics that modulate the levels of these chemicals may be helpful.
Most people believe probiotics are only useful in supporting healthy digestion. But, as researchers learn more about the gut-brain axis, they continue to learn more about effects of different probiotic strains on anxiety and depression, with some promising results emerging.
A recent review of studies on the relationship between probiotics (containing different Lactobacillus or Bifidobacterium strains) and depression shows they are effective when accompanied by antidepressants, but don't have as large an impact on their own. It's important to remember that if you choose to use probiotics for mental health, they should complement everything else you're doing, not replace it.
Can Probiotics Help with Stress, Anxiety & Mood?
Recent research on university students suggests that a daily dose of a probiotic mixture containing Lactobacillus fermentum, L. rhamnosus, L. plantarum, and Bifidobacterium longum can noticeably improve mood. Following a six-week study, participants who took the probiotic had a higher sleep quality and a significant reduction in depressive mood state, anger, and fatigue than did those who took a placebo.
These results suggest that probiotics could play a role in reducing sensitivity to negative situations, though more research is necessary to draw definite conclusions.
Lactobacillus rhamnosus & Depression
Evidence suggests that Lactobacillus bacteria may be a component of the best probiotic for depression. One species of this bacteria, L. rhamnosus, is a common probiotic species that you may use if you have gastrointestinal infections or diarrhea. Because of its popularity, it naturally became a strain used in many studies exploring the relationship between probiotics and mental health.
For instance, a randomized double-blind study supplemented a probiotic containing L. rhamnosus into women's diets from pregnancy until six months after delivery. The women who received the supplement reported significantly lower depression and anxiety scores in their postpartum period than the control group.
Bacillus coagulans & Anxiety
Bacillus coagulans produces lactic acid, like the Lactobacillus genus, but it also forms spores. This lets the dormant bacterial spores to survive in harsh conditions that may kill other probiotics. As a result, spore-forming probiotics have a longer shelf life and don't need refrigeration, which has made them popular in commercial products.
In a recent study of 40 people with IBS and major depression, participants who received the strain of Bacillus coagulans MTCC 5856 reported a significant decrease in their symptoms of clinical depression. It also had beneficial effects on sleeplessness. More research is still necessary to understand the underlying mechanism that causes these effects, however.
Lactobacillus plantarum & Depression
L. plantarum has many beneficial associations that could make it a component in probiotic products that target depression. Evidence suggests that different strains may have different impacts. For example, L. plantarum GKM3 may benefit memory, L. plantarum TWK10 may improve athletic ability, and other strains may play a role in combating health issues like:
- Anxiety using L. plantarum DR7
- High blood pressure
- Irritable bowel syndrome (IBS) using Lactobacillus plantarum 299v
- Diabetes using L. plantarum SS18-5
Now, research also indicates that L. plantarum 299v may improve cognitive function in people who have major depressive disorder.
L. plantarum PS128 & Anxiety
L. plantarum PS128 is a psychobiotic strain that appears to modulate important neurotransmitters and hormones.
In a 14-day trial of dogs that presented with behavioral issues, PS128 appeared to stabilize general emotional status and lessen the severity of their behavioral problems. It seemed to reduce the plasma serotonin depletion in dogs with anxiety, which is a similar mechanism to how some researchers believe selective serotonin reuptake inhibitors (SSRIs) work.
A study of L. plantarum PS128 on 200 patients with anxiety also showed clinical efficacy after taking the supplement twice a day for two months. The participants taking PS128 showed significantly larger improvements according to the Hamilton Anxiety scale than the study's control group, which took citalopram and sulpiride, two common drugs used to treat anxiety and depression.
Depression & the Gut-Brain Axis
The vagus nerve, which leads from the stomach and intestines directly to the brain, is important for signaling between the ENS and CNS. The messages it sends can influence your mood, among other body functions. As a result, an imbalance in neurotransmitters made in the gut puts you at a higher risk for mood imbalances, anxiety, and depression.
Your Microbiome Composition & Mental Health
Your gut microbiome plays a big role in the development and function of the hypothalamic-pituitary-adrenal (HPA) axis. This axis releases the stress hormone cortisol in fight-or-flight situations, giving your muscles the burst of energy they may need. However, to do this, cortisol alters immune system responses and other functions that would be nonessential in such an emergency.
This means that, if you're under stress for an extended time period or your HPA axis is overactive, the constant presence of cortisol weakens your immune system, putting you at risk for health problems like:
- Sleep problems
- Memory impairment
A study exploring the effect of supplementing Lactobacillus paracasei found that fatigue subjects who took it had lower cortisol levels, suggesting that probiotics could play a role in modulating an overactive HPA axis.
Serotonin's Role in the Gut-Brain Axis
Serotonin is the main neurotransmitter responsible for regulating your mood. If you're deficient in it, you may develop depression and possibly anxiety. This is why many antidepressants prevent reuptake of serotonin so that more remains present in the synapse between neurons where it can provide its signaling function.
Serotonin's other main functions include:
- Supporting digestion
- Helping maintain a healthy sleep cycle
- Promoting bone health
Most of your serotonin production happens in your gut. As a result, though the serotonin that your brain produces is vital for CNS neurons to function, chronic digestive issues like IBS or leaky gut can impair your serotonin production, harming your mental health.
But that does also imply that you can increase the amount of serotonin in your body by balancing the microbiome in your gut. Though you can't directly get serotonin from food, you can take other actions that promote serotonin production. For instance, you can:
- Eat more tryptophan-rich foods, like milk, bananas, turkey, and fish, because your cells use the amino acid tryptophan to make serotonin
- Get more exercise, because it has been shown to help modulate and naturally diversify the gut microbiome, which may support the increased presence of bacteria strains that produce serotonin, like L. plantarum
Do Probiotics Increase GABA?
GABA relaxes a neuron so that it receives, produces, and sends fewer messages. It produces a calming effect, which is why experts believe it plays a major role in controlling anxiety, stress, and fear. Conversely, low GABA activity can contribute to mood and brain function disorders like schizophrenia, depression, and anxiety.
GABA is present in some fermented foods, like kimchi, miso, and tempeh, and it can also be produced by certain species of probiotic bacteria. While GABA is not thought to cross the blood-brain barrier, it’s possible that GABA in the gut can affect the brain via the vagus nerve, which is part of the gut-brain axis. Initial studies in mice and humans suggest that a Lactobacillus probiotic or oral GABA supplements, respectively, can elicit a mental health benefit, but further research is needed.
Vitamin Deficiencies that Cause Depression & Anxiety
Probiotics aren't the only supplements that can potentially help with depression and anxiety. Eating a more balanced and colorful diet or taking a multivitamin can help improve any vitamin or mineral deficiency that might contribute to an issue.
Many vitamins support the body's biochemical reactions and promote healthy brain cell functions along with efficient neurotransmitter pathways. Being deficient in any of these vitamins can contribute to mental health disorders like depression or anxiety.
Many B vitamins can help influence your mood, fight fatigue, improve your memory, and give you more clarity. According to a review of many studies on B vitamins' effects on mental health, supplementing vitamin B in your diet can help reduce your stress, though the reviewer noted that it was difficult to compare the studies, since each had a different supplement concentration and design.
The major functions of the B vitamins are to help regulate the metabolism, convert nutrients into energy, create neurotransmitters, promote cell growth, and produce hormones and cholesterol.
People with a vitamin C deficiency often experience depressive symptoms and chronic fatigue. A recent study found that introducing vitamin C supplements to test subjects' diets increased their motivation to work and ability to focus on a task, leading to them performing better on cognitive tasks where they needed prolonged focus.
Vitamin D activates neurons' receptors, stimulates the release of neurotrophin, and helps keep the brain safe by strengthening antioxidant and anti-inflammatory defenses. It also strengthens metabolic and cardiovascular functions. The active vitamin D hormone, calcitriol, affects many neurotransmitters and neurotrophic factors that can influence mental disorders.
In fact, a study found that a deficiency disorder, hypovitaminosis D, is common among older adults and has a strong association with basic and executive cognitive functions, along with mental disorders like:
- Bipolar disorder
Other studies suggest that schizophrenia and autism could be more prevalent if babies have a prenatal vitamin D deficiency.
How Long Do Probiotics Take to Help with Stress & Anxiety?
Probiotics need time to harmonize with the gut environment. You also must take them regularly to see results. But, as long as you're doing everything right, most studies showed changes within four to eight weeks.
Taking a larger amount wouldn't speed up the process and could even cause you some discomfort. Some common side effects include:
This reaction shouldn't make you stop taking and benefiting from probiotics. The benefits of probiotics will come once your body has adapted. However, if these symptoms remain for more than a couple of weeks, you should check with your health care provider to determine if you should switch to a different probiotic.
The Future of Gut-Brain Medical Probiotics
It's hard to pin down exactly how probiotics affect someone's gut microbiome because so many other factors contribute to it, such as their diet and sleep quality. But many people have had positive results from using probiotics to help with their mental health, prompting further research. As more studies use the same strains, we'll be able to draw more conclusive trends on the best probiotics for different mental health-related goals.
Neuralli is the first neurologically active medical probiotic, with an active ingredient, L. plantarum PS128, clinically shown to benefit neurological health. It appears to affect dopamine and serotonin levels, likely via the gut-brain axis. If you want to try a gut-brain probiotic for yourself, Neuralli is a great place to start.