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.
What is L. lactis?
Lactococcus lactis is a lactic acid-producing Gram-positive species of bacteria 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 [1, 2, 3, 4, 5, 6] and human diseases . Its health benefits as a probiotic, however, are not as well-known or researched.
Note that this post is about Lactococcus lactis. For more information about the bacterium formerly known as Lactobacillus lactis, check out this post on L. delbrueckii.
Exopolysaccharide (EPS) of L. lactis increased catalase, superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activity, and decreased malondialdehyde (MDA) levels in mice .
Potential Benefits of L. lactis
L. lactis 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.
Insufficient Evidence For
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of L. lactis for any of the below-listed uses. Remember to speak with a doctor before taking L. lactis probiotic supplements, and never use them in place of something your doctor recommends or prescribes.
1) Skin Health
Ingestion of milk fermented with L. lactis increased sebum production, thereby potentially reinforcing the skin barrier in 23 healthy young women .
Ingestion of heat-killed L. lactis also maintained skin hydration and improved subjective skin elasticity in 30 middle-aged Japanese women .
Animal & Cell Research (Lacking Evidence)
No clinical evidence supports the use of L. lactis 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.
Yogurt fermented with L. lactis activated plasmacytoid dendritic cells (pDC), that are important for both innate and adaptive immune responses [11, 12], and susceptibility to infection .
It activated natural killer (NK) cells and enhanced their cytotoxic activity .
It improved resistance against pneumococcal infection, possibly by improving pathogen lung clearance, reduces lung injuries and increases the survival of infected mice [14, 15].
L. lactis-fed mice have drastically improved survival rate, reduced weight loss, and reduced lung damage when infected by murine parainfluenza virus (mPIV1)  or the H1N1 influenza virus .
Kefir-isolated L. lactis protect cells from C. difficile toxins .
Both live and heat-killed L. lactis reduced the severity of allergic response in mice [18, 19, 20].
It decreased the Th2 response  and induces a Th1-polarizing program in dendritic cells in mice .
It significantly attenuates atopic esophageal and bronchoalveolar eosinophilic inflammation in mice .
Ethanol can increase allergic responses. L. lactis was shown to restore oral tolerance in mice, by reducing local and systemic allergic outcomes such as IL-4 and IgE .
Oral treatment of newborn pigs with L. lactis significantly reduced the subsequent frequency of allergy, by dampening the Th-2 immune response .
Soy milk fermented with L. lactis exhibited anti-inflammatory effects and prevents IBD in mice [24, 25].
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 .
It reduced inflammatory cytokine production and nitric oxide expression in mice with colitis .
5) Heart Health
L. lactis reduced blood pressure, LDL cholesterol, and triglyceride contents in hypertensive rats .
Milk fermented by L. lactis exhibited systolic and diastolic blood pressure- and heart-rate-lowering effect in rats with hypertension .
Long-term oral intake of L. lactis suppressed the reduction of bone density and body weight in senescence-accelerated mice, a model of aging .
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 .
L. lactis inhibited the proliferation of lung cancer cells, colorectal cancer cells, gastric carcinoma cells and breast cancer cells .
The cytoplasmic fraction of L. lactis inhibited human stomach cancer cell proliferation and induces cancer cell death .
These cell studies may not be relevant at all for cancer treatment in animals or humans.
In cells and animals, researchers have observed that L. lactis:
- Decreased IL-4 in allergy [18, 34, 22] and increases IL-4 in infection .
- Decreased IL-8 [25, 27], IL-13 , and IL-18 .
- Increased [25, 35] and decreased IL-6 .
- Increased IL-10 [25, 14, 35] and IL-12 .
- Decreased IFN-γ  in inflammation and increased IFN-γ in allergy and infection [18, 35, 11].
- Decreased TNF-α in inflammation [27, 32] and increased TNF-α in infection and anti-tumor response [36, 14, 35].
- Increased Tregs bearing surface TGF-β .
- Decreased NO  and iNOS  in inflammation [a study where iNOS was increased: 36].
- Decreased MIP-2 .
- Decreased IgE [18, 22] and increased IgA, IgG , and IgG2 .
- Decreased NOD-1, NOD-2, TLR-4 , CCL11 (eotaxin-1), CCL17 (TARC)  and COX-2 .
- Inhibited the activity of angiotensin I-converting enzyme (ACE) .
L. lactis is mostly nonpathogenic in humans; however, a number of cases of infection with L. lactis have been reported over the years .
Some strains of L. lactis produce the biogenic amines putrescine and tyramine .
Probiotics should be avoided in patients with organ failure, immunocompromised status, and dysfunctional gut barrier mechanisms, where they may cause infections. To avoid adverse effects, talk to your doctor before starting any new probiotics.