L. paracasei is a beneficial probiotic species of bacteria that may benefit the immune system and gut microbiota and reduce allergic symptoms and skin sensitivity. What other potential health benefits could it have? Read on to find out.
What is Lactobacillus paracasei?
Lactobacillus paracasei is a gram-positive lactic acid bacterium, commonly used in dairy products and probiotics. Both L. paracasei and its fermented products are effective immunomodulators, they alleviate allergies, prevent gastric mucosal lesions and inhibit fat tissue accumulation .
Potential Benefits of L. paracasei
L. paracasei probiotic supplements have not been approved by the FDA for medical use and generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Possibly Effective For
A significant reduction of nasal symptoms and improved quality of life were achieved in patients with Japanese cedar pollinosis, who received L. paracasei when pollen scattering was low. However, the effects were limited during the peak period .
L. paracasei has allergy reducing effects in mice, by balancing the Th1/Th2 responses .
L. paracasei induces Th1 and regulatory responses in mice, suppresses airway inflammation, and down-regulates allergen-specific immune responses [4, 5].
L. paracasei administration to mothers during gestation/lactation protects against airway inflammation in offspring in mice .
At least five clinical studies with L. paracasei demonstrated clinically significant improvements in allergic rhinitis , one did not .
Subjects with a medical history of allergic rhinitis to grass pollen that received L. paracasei -fermented milk had lower nasal congestion and nasal itching .
In children with perennial allergic rhinitis, L. paracasei improved symptoms of sneezing, itchy nose, and swollen eyes .
L. paracasei improves the quality of life of subjects with persistent allergic rhinitis who are being treated with an oral H1-antihistamine. In this study, nasal symptoms had not changed, but ocular symptoms had consistently improved .
Heat-killed L. paracasei can effectively improve the overall quality of life for patients with allergic rhinitis induced by house dust mite in human subjects .
2) Skin Health
Heat-killed L. paracasei improved atopic dermatitis (AD) in adult patients .
According to some researchers, L. paracasei may help reinforce skin barrier function, inhibit water loss, decrease skin sensitivity and modulate the skin immune system leading to the preservation of skin homeostasis .
L. paracasei decreased skin sensitivity and increases barrier function recovery (water retention) in women .
3) Gut Health
L. paracasei increased the number of beneficial Bifidobacteria and Lactobacilli in human subjects [15, 16].
Oral intake of L. paracasei by mice increased intestinal Bifidobacteria and Lactobacilli [17, 18], and decreased the content of Clostridium perfringens .
L. paracasei antagonized Escherichia coli and Clostridium species [19, 16].
L. paracasei further increased acetic acid and butyric acid, while it decreases ammonia .
L. paracasei supplementation prevented bowel symptom onset in patients on long-term proton pump inhibitors .
L. paracasei normalized muscular activity and energy metabolism and elevates lipid breakdown in mice with irritable bowel syndrome (IBS) .
L. paracasei attenuated muscle hypercontractility and Th-2 levels in mice with post-infective irritable bowel syndrome (IBS) .
L. paracasei, in association with a high-fiber diet, reduced abdominal bloating and prolonged abdominal pain in patients with symptomatic uncomplicated diverticular disease .
L. paracasei resolved acute diarrhea  and ameliorated non-rotavirus-induced diarrhea in children .
L. paracasei-enriched artichokes relieved constipation in 20 patients .
L. paracasei modulated intestinal digestion, absorption of nutrients, energy metabolism, lipid synthesis and intestinal protective functions in mice .
Fermented milk with L. paracasei promoted intestinal epithelial cell growth and intestinal epithelial integrity to strengthen the intestinal barrier against chemical and inflammatory stimuli-induced damage .
L. paracasei synbiotic therapy prevented or repaired colon damage in mice with acute colitis, where this bacterium completely restored epithelial barrier integrity and gut protection [29, 30].
L. paracasei therapy prevents antibiotic induced visceral hypersensitivity and restores normal gut permeability in rats .
L. paracasei prevented intestinal inflammation in mice with colitis .
Oral supplementation of L. paracasei reduced the clinical progression of necrotizing enterocolitis in infants .
Insufficient Evidence For
Researchers are currently investigating whether L. paracasei has other health benefits. The potential benefits in this section have produced positive results in at least one clinical trial, but these studies are small, contradictory, or otherwise limited. Talk to your doctor before supplementing with L. paracasei for any reason.
Dietary supplementation with cow’s milk or rice fermented with L. paracasei prevented common infectious disease (CIDs) in children attending daycare .
L. paracasei enhanced systemic immunity in mice . This bacterium skewed the Th1/Th2 balance toward Th1 through the elevation of Th1 cytokine production [36, 17].
L. paracasei enhances natural killer (NK) cell activity, lymphocyte proliferation and antibody production in mice [37, 18, 38].
L. paracasei strongly induces IL-12, increases the proportion of natural killer (NK) cells in the spleen, and ameliorates the symptoms of influenza virus infection in mice [39, 40].
L. paracasei increases E. coli infection survival in mice .
Both L. paracasei and its supernatant enhance innate immunity through the activation of Toll-like receptor (TLR) signaling .
L. paracasei significantly increases the release of pro-inflammatory cytokines and stimulates the innate immune system in human enterocytes and dendritic cells (DCs) .
L. paracasei decreases pro-inflammatory cytokines and chemokines in human intestinal DCs challenged with Salmonella [41, 43].
5) Dental Health
Oral L. paracasei significantly reduced salivary S. mutans [44, 45, 46], and increased Lactobacilli in adults .
However, L. paracasei was not found efficient in 9-year-old children .
L. paracasei, even if heat-killed, inhibits S. mutans and decreases caries lesions in rats .
6) Fat Metabolism
L. paracasei decreased triacylglycerol in human subjects .
L. paracasei decreased energy/food intake in both human and animal subjects .
Water extract of L. paracasei reduced body weight in obese rats. It decreased the formation of lipid plaques in the aorta, reduced fat cell size and inhibits fat absorption, thereby reducing fat production (lipogenesis) .
In another study, the long-term ingestion of L. paracasei reduced body weight and abdominal fat weight in rats .
L. paracasei decreased body fat in mice .
Animal & Cell Research (Lacking Evidence)
No clinical evidence supports the use of L. paracasei for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
7) Liver Function
L. paracasei lowered liver fat deposition and serum ALT levels in mice with nonalcoholic steatohepatitis (NASH) .
L. paracasei reduced total blood and liver cholesterol in rats and decreased liver damage due to alcohol intake .
L. paracasei restored gut microbiota and attenuated ischemia/reperfusion-related liver injury in rats .
L. paracasei synbiotic (containing arabinogalactan, fructooligosaccharides) lessened NAFLD progression, lowered inflammatory markers, and reduced the severity of liver injury and insulin resistance in rats .
8) Insulin Resistance
L. paracasei synbiotic improved many aspects of insulin resistance, such as fasting response, hormonal homeostasis, and glycemic control in rats .
L. paracasei reduced the adverse effects of Zearalenone (ZEN), an estrogenic toxin produced by numerous Fusarium fungi species in pre- or post-harvest cereals in mice .
10) Urogenital Infections
L. paracasei prevented urogenital infections by inhibiting Staphylococcus aureus in mice .
11) Antibacterial Activity
L. paracasei inhibited common pathogens including Shigella dysenteriae, Staphylococcus aureus, Cronobacter sakazakii, Escherichia coli, and Candida albicans in the laboratory [60, 61].
Fermented milk with L. paracasei significantly improved gut microbiota, increased Lactobacilli, and inhibited the colonization of C. albicans to the intestines of mice .
A bacteriocin produced by L. paracasei inhibited P. gingivalis, a species of bacteria associated with periodontal disease .
Both viable and nonviable L. paracasei exert the same antiproliferative and proapoptotic effects on gastric and colorectal cancer cells in the laboratory .
L. paracasei significantly inhibits colon cancer cell proliferation .
However, L. paracasei has not been investigated in animals, let alone in humans, so these should not be taken as indicative of any clinical effect. Furthermore, people are often immunocompromised during cancer treatment, so it’s especially important to talk to your doctor before taking probiotics if you are being treated for cancer.
Mechanism of Effect
Researchers have conducted a number of cell and animal studies to investigate the effect of L. paracasei on a biochemical level. Here are some of their findings:
- Depending on the experimental setting, L. paracasei had different effects on cytokines.
- It both elevated and suppressed pro-inflammatory cytokines TNF-α [28, 29, 30, 36, 65], decreased [30, 32] or increased IL-1β [36, 65], and inhibited  or elevated IFN-γ [36, 65].
- L. paracasei mostly induced IL-12 [40, 66, 36, 39] [in some studies decreased: 42, 32], and increased the proportion of NK cells , while reducing the Th-2 response [22, 67].
- L. paracasei mostly increased IL-10 [29, 36, 65, 68] [a study where IL-10 is decreased: 42].
- L. paracasei decreased TGF-β1 [42, 22], and increased TGF-β2 .
- L. paracasei increased IL-8 , decreased IL-2, IL-4, IL-5, and IL-13 [36, 4, 8, 54]. and both decreased and increased IL-6 [32, 42].
- L. paracasei increased IgA [65, 68], and decreased IgG4  and IgE .
- L. paracasei stimulated iNOS and NO .
- L. paracasei increased RANTES, IP-10  and ANGPTL4 .
- L. paracasei lowered PPAR-γ [54, 51].
- It decreased MIP-1α , CCL-20 , PTGS2 , COX-2, PGE2 , TLR-4, NOX-4, MCP-1, PPAR-δ , CCAAT/ C/EBPβ, C/EBPα and HR-LPL .
- L. paracasei increased CD4+ T cell and B cell proliferation  and upregulated the CD4+CD25+Foxp3+Treg cell responses .
- It reduced neutrophil infiltration  and attenuated eosinophil influx in the lungs [67, 4, 8].
- L. paracasei increased the expression of almost all TLR signaling genes .
Oral administration of L. paracasei had no adverse effects in mice  and rats .
However, the use of probiotics should be avoided in patients with organ failure, immunocompromised status, and dysfunctional gut barrier mechanisms, where L. paracasei can cause infection .
To avoid adverse effects and unexpected interactions, talk to your doctor before starting any new probiotics.