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L. lactis is a commonly used probiotic whose health benefits we are just beginning to understand. This bacterium boosts the immune system, may combat allergies, hypertension, and IBD, and has beneficial effects on the skin.


Lactococcus lactis is a lactic acid producing Gram-positive bacterium used extensively in the production of buttermilk, cheese, pickled vegetables and other fermented products.

L. lactis is often studied as a genetically modified organism for the treatment of animal (R,R,R,R,R,R) and human disease (R). Its health benefits as a probiotic, however, are less known and researched.

Note that this post is about Lactococcus lactis. For more information about Lactobacillus lactis check out the post about L. delbrueckii.

Health Benefits of L. lactis

1) L. lactis Boosts Immunity


Yogurt fermented with L. lactis activates plasmacytoid dendritic cells (pDC), that are important for both innate and adaptive immune responses (R,R), and lowers the risk of common cold in human subjects (R).

L. lactis activates natural killer (NK) cells and enhances their cytotoxic activity (R).

L. lactis improves resistance against pneumococcal infection by improving pathogen lung clearance, reduces lung injuries and increases survival of infected mice (R,R).

L. lactis-fed mice have drastically improved survival rate, reduced weight loss, and reduced lung damage when infected by murine parainfluenza virus (mPIV1) (R) the influenza  virus (H1N1) (R).

Kefir-isolated L. lactis protect cells from C. difficile toxins (R).

2) L. lactis May Alleviate Allergies


Both live and heat-killed L. lactis ameliorate the allergic response in mice (R,R,R).

L. lactis decreases the Th2 response (R) and induces a Th1-polarizing program in dendritic cells in mice (R).

L. lactis significantly attenuates atopic esophageal and bronchoalveolar eosinophilic inflammation in mice (R).

Ethanol can increase the allergic response. L. lactis was shown to restore oral tolerance in mice, by reducing local and systemic allergic outcomes such as IL-4 and IgE (R).

Oral treatment of newborn pigs with L. lactis significantly reduced the subsequent frequency of allergy, by dampening the Th-2 immune response (R).

3) L. lactis May be Beneficial in IBD

Soy milk fermented with L. lactis exhibits anti-inflammatory effects and prevents IBD in mice (R,R).

Administration of heat-killed L. lactis suppressed IBD symptoms, such as shortening of colon length, damage to the colon mucosa, and spleen enlargement in mice (R).

L. lactis reduced inflammatory cytokine production and nitric oxide expression in mice with colitis (R).

4) L. lactis is Beneficial for the Skin


L. lactis increased sebum content, thereby potentially reinforcing the skin barrier in healthy young women (R).

L. lactis strain maintained skin hydration, and improved subjective skin elasticity in middle-aged Japanese women (R).

5) L. lactis exhibits Antioxidant Properties

Exopolysaccharide (EPS) of L. lactis increased catalase , superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, and decreased malondialdehyde (MDA) levels in mice (R).

6) L. lactis May Lower Blood Pressure

L. lactis reduces blood pressure, LDL cholesterol and triglyceride contents in hypertensive rats (R).

Milk fermented by L. lactis exhibits systolic and diastolic blood pressure- and heart-rate-lowering effect in rats with hypertension (R).

7) L. lactis May be Beneficial in Aging

Long-term oral intake of L. lactis suppressed the reduction of bone density and body weight in senescence-accelerated mice (R).

L. lactis May Prevent Age-Related Hearing Loss

Intake of heat-killed L. lactis altered the intestinal flora, affected plasma metabolite levels, including fatty acid levels, and slowed down age-related hearing loss in mice, by inhibiting the loss of neurons and hair cells in mouse inner ear (R).

8) L. lactis May Combat Cancer

L. lactis inhibits the proliferation of lung cancer cells, colorectal cancer cells, gastric carcinoma cells and breast cancer cells (R).

Cytoplasmic fraction of L. lactis inhibits human stomach cancer cell proliferation and induces cancer cell death (R).


  • L. lactis decreases IL-4 in allergy (R,R,R) and increases IL-4 in infection (R).
  • L. lactis decreases IL-8 (R,R), IL-13 (R), and IL-18 (R).
  • L. lactis can both increase (R,R) and decrease IL-6 (R).
  • L. lactis increases IL-10 (R,R,R) and IL-12 (R).
  • L. lactis decreases IFN-γ (R) in inflammation and increases IFN-γ in allergy and infection (R,R,R).
  • L. lactis decreases  TNF-α in inflammation (R,R)  and increases TNF-α in infection and anti-tumor response (R,R,R).
  • L. lactis can increase CD4+ T Tregs bearing surface TGF-β (R).
  • L. lactis decreases NO (R) and iNOS (R) in inflammation (a study where iNOS was increased: R).
  • L. lactis decreases and MIP-2 (R).
  • L. lactis decreases IgE (R,R) and increases IgA, IgG (R), and IgG2 (R).
  • L. lactis decreases NOD-1, NOD-2, TLR-4 (R), CCL11 (eotaxin-1), CCL17 (TARC) (R) and COX-2 (R).
  • L. lactis inhibits the activity of angiotensin I-converting enzyme (ACE) (R).


L. lactis is mostly nonpathogenic in humans, however, a number of cases of infection with L. lactis have been reported over the years (R).

Some strains of L. lactis increase biogenic amines putrescine and tyramine (R).

Probiotics should be avoided in patients with organ failure, immunocompromised status, and dysfunctional gut barrier mechanisms, where they may cause infections.

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  • Karl

    I think the should mention that this bacteria is transient and does not colonize the gut so you’d have to continuously keep taking this probiotic to get the benefits.

  • Mark Mark

    What if someone has had their appendix removed? Can they use probiotics? How otherwise can they care for the gut?

  • Jack Cameron

    In your introduction you mention “Yogurt fermented with L. lactis.”
    I think it would be clearer to use the term “mesophillic fermented milk” rather than “yogurt”. According to my dictionary, “yogurt” is a dairy product that is fermented at “thermophillic” temperatures.
    The optimum temperature for lactoccus lactis is 77 to 86 degrees F. As temperatures increase above 86 degrees F the growth of lactococcus lactis slows while other bacteria such as lacto bacillus become more dominant. The optimum temperature for thermophillic bacteria is 100 to 122 degrees F at which temperature practically no lactococcus lactis bacteria survive. Yogurt that is produced at thermophillic temperatures contains little, if any, lactococcus lactis and does not produce either K vitamin (long chain menaquionones) or nisin (a potent preservative) and does not break down galactose (as best I can determine).
    Jack Cameron

  • Jack Cameron

    I found your article on lactococcus lactis of great interest. For several years I have been making “clabber”, which is raw milk fermented at room temperature (mesophilic fermentatiion) . Lactococcus lactis in naturally present in raw milk and thrives at low temperature and low pH. Fermented cheese is also fermented with lactococcus lactis. Occasionally I buy lactococcus lactis starter online and use it to boost the lactococcus lactis content of my clabber.

    One aspect of lactococcus lactis that you did not mention is that it synthesizes long chain menaquinones, mainly MK8 and MK9, which are often referred to as vitamin K2. Vitamin K1 comes from green vegetables and is essential for blood coagulation and for activation of vitamin K dependent proteins. The menaquinones from dairy fermentation do the same thing but more potent than K1.

    A study was conducted in Sweden around 2014 of 60,000 women folled for 20 years that found that women who drank the most milk had higher risk if all-cause mortality, CVD mortality, cancer mortality, and hop fracture. In contrast, those who consumed the most fermented milk and cheese had a LOWER risk of cvd mortality, all-cause mortality, cancer mortality and hip fracture. (PMID 25352269)
    It was hypothesized that the increased risk of milk was due to galactose which is produced when lactose is digested to form D-galactose and D-glucose.
    Fermentation by lactococcus lactis breaks down galactose (the thermophilic bacteria in yogurt does not break down galactose) which, it was hypothesized, resulted in reduced risk from fermented dairy products, The article details other factors dairy fermented by lactococcus lactis reduce risk, many of which you have mentioned.

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