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Do You Feel Sad, Stressed Out and Can't Sleep? Maybe it's Time to Try Probiotics

We've all heard of how good probiotics are for our gut biome. But what if I told you these little bacteria could help you achieve both a happy gut AND a happy brain? Recent studies suggest that some bacteria can do more than help our digestion and benefit our mood and sleep.

Photo from Myriams-Fotos on Pixabay

The gut biome (sometimes called the "microbiome") is the assortment of microorganisms living in our digestive tract. The variety and abundance of microorganisms in our gut are pretty amazing. For example:

  • Over 1,000 different species of bacteria live in our gut

  • In addition to bacteria, our gut also contains fungi, protists, and viruses

  • Trillions of microorganisms like bacteria live in the gut of a single person

While numerous bacterial species exist, some species have been found to be especially beneficial for our mood and quality of sleep. A strain of probiotics found in the Yakult probiotic drink (Lacticaseibacillus strain Shirota (LcS)) has been observed to produce these benefits. Researchers at the National Center of Neurology and Psychiatry in Tokyo, Japan, demonstrated that a daily dosage of two yogurt drinks amounting to a total of 80 billion colony forming units (CFU) of LcS was associated with decreased depressive symptoms and better sleep (Otaka, 2021). They performed a 12-week trial with 18 patients (4 males, 14 females, mean age of 40.6 years) who had a major depressive disorder or bipolar disorder. Improvements in mood and sleep were measured through the State-Trait Anxiety Index, Pittsburgh Sleep Quality Index, and Hamilton Depression Rating Scale, 21-item version. Gut microbiota analysis demonstrated that an increased concentration of probiotics (specifically Bifidobacterium and Atopobium) in the gut biome due to LcS supplementation was moderately correlated with better sleep quality and decreased anxiety and depressive symptoms.

Two important benefits of LcS from these studies were:

  • LcS resulted in a 38% decrease in Hamilton Depression Rating Scale

  • LcS decreased the Pittsburgh Sleep Quality Index by 18.8% (lower index indicates better quality sleep)

The effects of LcS on sleep are further supported by a study from Tokushima University, Japan, which examined a group of 124 4th year medical students (55 males, 39 females, mean age of 22.7 years) (Takada, 2017). 100mL of fermented milk containing LcS (1.0×109 CFU/mL) was administered daily to the experimental group for eight weeks before and three weeks after a national standardized examination, for a total duration of 11 weeks. Sleep quality was measured through the Pittsburgh Sleep Quality Index, single-channel sleep electroencephalogram, and Oguri-Shirakawa-Azumi sleep inventory scores. The experimental group displayed a substantial increase in delta wave intensity and maintenance of stage 3 sleep, which are involved with deep sleep and a subjective increase in sleep quality. These results were statistically significantly different when compared to the control group. It is important for students to obtain 7-8 hours of quality sleep before important examinations, and the current research suggests that certain probiotics, specifically LcS, may be useful in promoting this.

Are the benefits in mood and sleep only observed when LcS is ingested? Studies utilizing a different probiotic strain, Lactobacillus gasseri CP2305 (L. gasseri), reported similar effects (Nishida, 2019). A trial using Lactobacillus gasseri CP2305 was conducted on 60 Japanese medical students (41 males, 19 females) preparing for the national examination for medical practitioners. The intake of a daily dosage of 10 billion CFU in tablet form for 24 weeks was associated with a significant reduction in anxiety and sleep irregularity. Stress and anxiety levels were recorded through several tests, including State-Trait Anxiety Index, 28-item General Health Questionnaire, Hospital Anxiety and Depression Scale, and salivary cortisol levels. The Pittsburgh Sleep Quality Index and single-channel sleep electroencephalogram were used to assess sleep quality. Salivary cortisol levels, State-Trait Anxiety Index-trait anxiety, and Hospital Anxiety and Depression Scale scores were significantly reduced in the experimental group compared to the control, indicating lower stress levels and reduced depressive symptoms. Delta wave power was observed to increase by 10% in the probiotic group than in control during stage 3 of sleep, indicating improved quality of deep sleep. Just like LcS, L. gasseri also can provide similar benefits for anxiety and sleep. Nishida's study also showed the following benefits:

  • Wake time after sleep onset decreased by 18.5% in the probiotic group compared to 4% in the control group after 24 weeks.

  • Time from fully awake to sleeping decreased by 25% in the probiotic group, while it increased by 18.3% in the control group after 24 weeks.

Why do we need to alter our gut biome to see benefits?

For some of us, we don't. We may already be eating sufficient advantageous probiotics on a regular basis that provides the benefits discussed. However, for a large proportion of the population, especially for high school and college students, who don't prioritize proper nutrition, it is common to have an imbalance in the beneficial bacteria in their gut.

What Causes an Imbalance in the Gut Bacteria?

Many factors affect the composition and number of gut bacteria present in individuals. Some of the major factors that affect our gut bacteria:

  • Use of antibiotics

  • Use of steroids

  • Exposure to heavy metals and other toxins

  • Lack of breast-feeding as a baby

  • Food poisoning

  • Food allergies

Overall, the current evidence strongly supports the beneficial effects of probiotics on our mood and sleep. What is the possible mechanism(s) that allows these bacteria to do this? While having regular bowel movements can certainly contribute to better overall wellbeing, there seems to be more to it. Other bacteria have been shown to inhibit the growth of pathogenic microorganisms in the gut, reduce the pH in the colon, and aid in the production of bioactive metabolites (such as vitamin B1, folate, levans, and butyric acid) (Hill, 2014). Concerning mood-enhancing probiotics, some researchers speculate that the proliferation of these probiotic strains can stimulate the gut-brain axis in ways that may modulate stress levels and anxiety. The brain and the gut are directly connected through the vagus nerve that runs from the intestines to the brainstem. Hence, some scientists refer to the gut as the "second brain." However, more research is needed to understand the gut-brain axis (Nishida, 2019).

There are also limitations to the studies presented that should be noted. As most of these studies investigate the effects of specific strains, it is difficult to generalize the results to the typical cocktails of probiotics found naturally in food and supplements. The studies were mainly conducted on young adults of Japanese ethnicity, and it's possible that these results may not be generalized to those of different ethnicity and age. Nonetheless, while more research is needed to better understand the mechanisms in which these probiotics act to improve our mood and sleep, current research supports the mood and sleep enhancing benefits of a daily dosage of approximately 1 × 1010 CFU of probiotic strains such as Lacticaseibacillus paracasei and Lactobacillus gasseri.

Not sure how to increase your probiotic gut content? Try one or more of these natural sources for probiotics.

  • Yogurt

  • Kimchi

  • Kefir

  • Natto

  • Miso

  • Some types of cheese (cottage cheese, gouda, cheddar, mozzarella)

  • Kombucha

  • Saltwater brined green olives

  • Sauerkraut

  • Tempeh

You can also take probiotic supplements. However, don't expect results after one day, as the studies discussed were all done over weeks. So next time you're feeling down or unable to sleep, consider adding regular probiotic drinks or food to your menu.

Written by Irene Park and edited by Aldrin V. Gomes, PhD, FCVS, FAHA


Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, et al. (2014) The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 11:506-14

Nishida, K, Sawada, D, Kuwano, Y, Tanaka, H., Rokutan, K. (2019) Health Benefits of Lactobacillus gasseri CP2305 Tablets in Young Adults Exposed to Chronic Stress: A Randomized, Double-Blind, Placebo-Controlled Study. Nutrients vol. 11, 8:1859

Otaka, M, Kikuchi-Hayakawa, H, Ogura, J, Ishikawa, H, Yomogida, Y, et al. (2021) Effect of Lacticaseibacillus paracasei Strain Shirota on Improvement in Depressive Symptoms, and Its Association with Abundance of Actinobacteria in Gut Microbiota. Microorganisms vol. 9, 5:1026

Takada, M., Nishida, K, Gondo, Y, Kikuchi-Hayakawa, H, Ishikawa, H, Suda, K et al. (2017) Beneficial Effects of Lactobacillus Casei Strain Shirota on Academic Stress-Induced Sleep Disturbance in Healthy Adults: A Double-Blind, Randomised, Placebo-Controlled Trial. Beneficial Microbes, vol. 8, 2:153–62

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