What This Strain Does
Lactobacillus casei is a versatile and well-researched probiotic strain that naturally inhabits the human gastrointestinal tract and is also commonly found in fermented foods, particularly aged cheeses where it contributes to flavor development. The species has been reclassified to Lacticaseibacillus casei under updated bacterial taxonomy, though it continues to be widely known by its traditional name in consumer products and even most scientific literature.
This bacterium demonstrates remarkable adaptability, thriving across a wide range of temperatures and pH levels. It can survive stomach acid and bile salts effectively, ensuring that viable bacteria reach the intestines where they can exert their beneficial effects. L. casei is closely related to L. rhamnosus and L. paracasei, and these species often work synergistically when combined in probiotic formulations.
L. casei works through multiple mechanisms to support digestive and immune health. It produces lactic acid that lowers intestinal pH, creating an environment that favors beneficial bacteria while inhibiting pathogens. The strain also produces bacteriocins, natural antimicrobial compounds that directly kill harmful microorganisms. Additionally, L. casei can help break down complex carbohydrates and dietary fibers, reducing fermentation that might otherwise cause gas and bloating.
The immune-modulating effects of L. casei are particularly noteworthy. The strain interacts with immune cells in the gut-associated lymphoid tissue, enhancing natural killer cell activity and modulating cytokine production. These effects translate to improved resistance against infections, reduced duration of illness, and potential anti-inflammatory benefits that extend beyond the digestive system.
Research also suggests that L. casei influences bowel regularity, with several studies showing improvements in constipation symptoms. The strain appears to accelerate intestinal transit time and increase stool frequency, making it a relevant choice for those dealing with slow digestion.
Research Highlights
L. casei has been extensively studied across multiple health applications, with particularly strong evidence for immune function and digestive health.
A landmark study published in the European Journal of Clinical Nutrition examined the effects of daily L. casei Shirota consumption on winter infections. Over a four-month period, participants consuming the probiotic experienced significantly shorter duration of upper respiratory infections and reduced severity of symptoms compared to control groups. The immune-enhancing effects were attributed to increased natural killer cell activity.
Research published in the British Journal of Nutrition investigated L. casei DN-114001 for preventing common infectious diseases in elderly nursing home residents. The study found that daily consumption significantly reduced the incidence of respiratory and gastrointestinal infections in this vulnerable population, with particularly notable reductions in pneumonia risk.
For constipation, a randomized controlled trial published in Alimentary Pharmacology and Therapeutics demonstrated that L. casei Shirota significantly increased stool frequency and improved stool consistency in adults with chronic constipation. Participants experienced meaningful improvements in bowel function within two to four weeks of starting supplementation.
A study in the World Journal of Gastroenterology examined L. casei for irritable bowel syndrome symptoms. After eight weeks of supplementation, participants showed significant improvements in abdominal pain, bloating, and overall symptom scores compared to placebo. The benefits were most pronounced for those with constipation-predominant IBS.
Anti-inflammatory research published in Clinical and Experimental Immunology found that L. casei supplementation reduced inflammatory markers including C-reactive protein and certain pro-inflammatory cytokines in adults with metabolic concerns, suggesting systemic anti-inflammatory effects beyond the gut.
Specific Strains to Look For
Several specific L. casei strains have accumulated significant research and are worth seeking out when selecting products.
L. casei Shirota is the most extensively researched strain, originally isolated by Japanese scientist Minoru Shirota in 1930. This strain is the active ingredient in Yakult and has been studied in hundreds of scientific papers. Research supports its use for immune enhancement, digestive regularity, and overall gut health. It’s particularly well-documented for reducing respiratory infection duration and improving constipation.
L. casei DN-114001 (marketed in some products as L. casei Immunitas or Defensis) has been specifically studied for immune function, with research demonstrating reduced infection rates in elderly populations. This strain is found in certain Dannon products and has solid evidence for reducing common infectious diseases.
L. casei CL1285 is frequently combined with L. acidophilus for preventing antibiotic-associated diarrhea and Clostridioides difficile infection. Multiple hospital-based studies have demonstrated the effectiveness of this combination, making it a relevant choice for those taking antibiotics.
L. casei Zhang is a strain that has shown promise in research for cholesterol reduction and general metabolic health, though it’s less commonly available in commercial products outside of Asia.
What to Look For in Products
Quality L. casei supplements share several characteristics that indicate effectiveness and reliability.
Dosage requirements vary by application. For immune support, most studies use between 1 billion and 10 billion CFU daily. For constipation and digestive regularity, doses of 6-20 billion CFU have been used in clinical research. The strain L. casei Shirota is often delivered in smaller CFU counts (billions rather than tens of billions) with demonstrated effectiveness, suggesting that strain selection may matter more than sheer bacterial count.
Strain identification is essential for predictable benefits. Products should specify which L. casei strain they contain rather than simply listing the species. The extensive research behind strains like Shirota doesn’t necessarily apply to unspecified L. casei strains.
Fermented dairy products, particularly certain probiotic yogurts and drinks, can be effective delivery systems for L. casei. The strain has a natural affinity for dairy environments and may maintain good viability in these products. Yakult remains the most well-documented L. casei product, with its effectiveness demonstrated across numerous clinical trials.
Combination products pairing L. casei with complementary strains like L. acidophilus, L. rhamnosus, or Bifidobacterium species may offer synergistic benefits. The L. casei and L. acidophilus combination has particularly good evidence for preventing antibiotic-associated complications.
Look for products with viability guarantees through the expiration date and third-party testing verification from organizations like USP, NSF, or ConsumerLab.
Potential Side Effects
L. casei has demonstrated excellent safety across decades of commercial use and extensive clinical research, including studies in vulnerable populations such as the elderly and hospitalized patients.
Initial use may cause temporary mild gas, bloating, or changes in bowel habits as the gut microbiome adjusts. These symptoms typically resolve within one to two weeks and are less common with gradual dose introduction.
Those who are severely immunocompromised, have central venous catheters, or are critically ill should consult healthcare providers before using L. casei or any probiotic, as rare cases of infection have been reported in these highly vulnerable populations.
People with milk allergies should check product formulations carefully, as many L. casei products are dairy-based or cultured on milk-based media. Dairy-free options are available for those who need to avoid milk proteins.
L. casei is generally considered a moderate histamine producer, which may be relevant for those with histamine intolerance. Individuals sensitive to histamine may want to start with low doses and monitor their response carefully.
How to Take
L. casei can be taken with or without food. Consuming it with a meal, particularly one containing some fat, may enhance survival through stomach acid, though the strain demonstrates good acid tolerance regardless of timing.
For immune support during cold and flu season, daily supplementation starting before the season begins and continuing throughout may provide the best protection. Studies showing immune benefits typically used supplementation periods of three to six months.
For constipation, benefits typically appear within two to four weeks of consistent daily use. Taking L. casei in the morning may align with natural circadian rhythms of gut motility, though evidence for optimal timing is limited.
When using L. casei during antibiotic treatment, particularly in combination with L. acidophilus for preventing diarrhea, separate the probiotic dose from antibiotics by at least two hours. Continue supplementation for one to two weeks after completing the antibiotic course.
Fermented dairy products containing L. casei can be consumed as part of a daily routine, with research typically using one to two servings per day. These products may be particularly appealing for those who prefer food-based probiotic sources.
Key Takeaways
L. casei is a versatile probiotic with strong evidence for enhancing immune function, improving digestive regularity, and reducing inflammation.
The strain L. casei Shirota (found in Yakult) is the most extensively researched and has demonstrated benefits for reducing respiratory infection duration and improving constipation.
Research shows L. casei can reduce the duration and severity of winter infections by enhancing natural killer cell activity and other immune parameters.
For constipation, studies demonstrate improved stool frequency and consistency within two to four weeks of daily supplementation.
The combination of L. casei with L. acidophilus has good evidence for preventing antibiotic-associated diarrhea and C. difficile infection.
Available in both supplement form and fermented dairy products, with probiotic drinks offering a well-researched food-based option.