L. acidophilus is a common and popular probiotic bacterium. People use it to lower cholesterol, improve gut health, and suppress allergies, but does it work? And what other benefits might it have? Read on to find out.
What is Lactobacillus acidophilus?
Lactobacillus acidophilus is a gram-positive lactic acid bacterium, that has been traditionally and widely used in the dairy industry, and more recently as a probiotic .
L. acidophilus is added to commercial yogurts and dairy formulations both for its flavor and for probiotic effect and is one of the most commonly selected Lactobacillus species for dietary use .
Potential Benefits of L. acidophilus
L. acidophilus probiotic supplements have not been approved by the FDA for medical use. Supplements 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
1) Iron Status
Iron deficiency was associated with low levels of Lactobacilli in a small study of young women in south India .
190 preschool children supplemented with L. acidophilus exhibited higher red blood cell status  and a significant reduction in the prevalence of anemia .
L. acidophilus increases iron bioavailability in rats .
In multiple clinical studies, daily consumption of L. acidophilus or a fermented product containing L. acidophilus after each dinner contributed to a significant reduction in cholesterol . However, in another study, L. acidophilus did not lower blood cholesterol in men and women with normal to borderline high cholesterol levels .
L. acidophilus reduces cholesterol and LDL-cholesterol in mice fed a high-fat diet .
L. acidophilus lowers total blood cholesterol, LDL-cholesterol, and TAG, and total liver cholesterol and liver TAG in rats [9, 10].
3) Cardiovascular Disease
L. acidophilus consumption led to a 2.4% to 3.2% reduction in blood cholesterol in clinical studies. Since every 1% reduction in serum cholesterol concentration is associated with an estimated 2% to 3% reduction in risk for coronary heart disease, the authors argued, regular intake of L. acidophilus has the potential to reduce the incidence of coronary heart disease by 6 to 10% .
L. acidophilus protected against atherosclerosis through the inhibition of intestinal cholesterol absorption in mice fed a Western diet .
L. acidophilus reduced cholesterol and inhibited the accumulation of lipoprotein in atherosclerotic plaques in mice .
L. acidophilus attenuated the development of atherosclerotic lesions in mice, possibly by reducing oxidative stress and inflammatory response .
4) Gut Health
Healthy volunteers receiving L. acidophilus and cellobiose showed increased levels of Lactobacilli, Bifidobacteria, Collinsella, and Eubacterium, while Dialister was decreased .
L. acidophilus increased the population of Lactobacilli and Bifidobacteria in rats .
L. acidophilus administered in yogurt positively shifted gut microbiota and increased intestinal Bifidobacteria in obese mice .
L. acidophilus increased Lactobacilli and Bifidobacteria populations, increased levels of acetic, butyric, and propionic acids, and lowered ammonium in a human microbiota simulator .
L. acidophilus administered with amoxicillin/clavulanate was associated with a significant decrease in patient complaints of GI side effects and yeast superinfection .
Some trials found no beneficial effect on the prevention of travelers’ diarrhea  or acute diarrhea in children .
Other studies show that heat-killed L. acidophilus markedly improved symptoms in patients with chronic diarrhea , L. acidophilus reduced the duration of diarrhea in hospitalized, but not outpatient, children , and ameliorated both rotavirus-positive diarrhea  and nonrotavirus diarrhea in children .
L. acidophilus attenuates diarrhea in mice .
L. acidophilus reduced abdominal pain and discomfort in patients with irritable bowel syndrome (IBS) [26, 27].
L. acidophilus improves intestinal inflammation caused by H. pylori  and decreases the viability of H. pylori and increases the eradication rate in infected patients .
5) Atopic Dermatitis
L. acidophilus suppressed Th2-dominant inflammation by activating regulatory T cells and Th1 helper T cells in atopic dermatitis .
Long-term oral administration of L. acidophilus significantly restored Th1/Th2 balance and ameliorated the symptoms of atopic dermatitis in children .
Prolonged ingestion of L. acidophilus significantly decreased eczema area and severity index in patients with adult atopic dermatitis [30, 32]. The probiotic also suppressed scratching .
L. acidophilus suppresses ear swelling, scratching behavior and other dermatitis-like symptoms in mice [33, 34].
L. acidophilus alleviated allergic symptoms in patients with Japanese cedar pollinosis [35, 36].
L. acidophilus alleviated the symptoms in patients with perennial allergic rhinitis .
L. acidophilus may also improve lactose digestion and tolerance, though the evidence is conflicting [38, 39].
L. acidophilus suppressed hypersensitivity, attenuates the numbers of inﬂammatory cells and inhibited Th17 and IgE production in mice with allergy .
L. acidophilus increased the number of Treg cells to suppress the progression of allergic contact dermatitis in mice  and suppressed nasal symptoms and IgE in allergic mice [35, 42].
7) Vaginal Infections
Treatment of patients with bacterial vaginosis with L. acidophilus contributed to the restoration of a normal vaginal environment .
L. acidophilus maintained low pH and increased human vaginal epithelial cell viability .
Daily ingestion of yogurt enriched with L. acidophilus appeared to reduce the incidence of bacterial vaginosis .
Insufficient Evidence For
Researchers are currently investigating whether L. acidophilus 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. acidophilus for any reason.
8) Folate and B12 Status
Daily consumption of L. acidophilus significantly improved vitamin B12 and folate levels in children .
L. acidophilus preserved insulin sensitivity in men with type 2 diabetes mellitus .
10) Minimal Hepatic Encephalopathy
L. acidophilus improved blood ammonia and cognitive function in patients with minimal hepatic encephalopathy (MHE). Furthermore, patients who received the probiotic were less likely to develop overt encephalopathy .
L. acidophilus increased Bifidobacteria levels and beneficially changes microbiota in elderly subjects .
Dahi containing L. acidophilus reversed age-related immune function decline in mice .
Dahi containing L. acidophilus reduced oxidative stress and prevented molecular alterations associated with aging in mice .
L. acidophilus reversed immune defects in fatigued athletes . It also decreased chronic fatigue following exercise and attenuated stress in rats .
Animal Research (Insufficient Evidence)
No clinical evidence supports the use of L. acidophilus 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.
L. acidophilus enhanced natural and acquired immunity in healthy mice .
Both live and non-live L. acidophilus protected against influenza virus (H1N1) infection in mice .
L. acidophilus can effectively prevent bacteria-induced colitis by limiting infection and promoting mucosal protective regulatory immune responses in mice .
L. acidophilus suppressed all of the 74 gram-negative and 16 of the gram-positive bacteria found in burn wounds, which can cause burn wound infections .
L. acidophilus may reduce mutant Streptococcus in dental plaque, and may decrease the cariogenic potential of oral streptococci .
L. acidophilus alleviated inflammation in human intestinal epithelial cells , decreased the transcriptional activity of NF-κB, and inhibited proinflammatory cytokines .
L. acidophilus decreased arthritis symptoms and maintained normal histology of reproductive organs in rats .
L. acidophilus showed effects comparable to the drug indomethacin in decreasing organ damage associated with arthritis in rats. This probiotic down-regulated pro-inflammatory and up-regulated anti-inflammatory cytokines .
16) Pain Perception
Oral administration of L. acidophilus induced the expression of mu-opioid and cannabinoid receptors in intestinal epithelial cells and mediated analgesic function in the gut, similar to the effects of morphine .
L. acidophilus promoted gastric ulcer healing in rats .
18) GI Infections
L. acidophilus alleviated E. coli infection in mice .
L. acidophilus inhibited the growth of C. difficile, a pathogenic bacterium that causes antibiotic-associated diarrhea  and inhibited the growth of Salmonella enterica in mice, especially when administered after the infection .
19) GI Inflammation
L. acidophilus counteracted inflammation in intestinal epithelial cells .
Treatment with L. acidophilus significantly increased butyrate uptake in intestinal epithelial cells. Butyrate plays beneficial roles serving as a primary fuel, ameliorating mucosal inflammation, and stimulating salt absorption .
L. acidophilus had a protective effect on the development of necrotizing enterocolitis (NEC) in rats .
L. acidophilus improved inflammatory and functional aspects of intestinal mucositis caused by chemotherapy in mice .
L. acidophilus protected against colitis-induced weight loss and increases beneficial Lactobacilli and Bifidobacteria in the distal colon in mice .
L. acidophilus reduced intestinal inflammation following infection in newborn mice .
Researchers are currently investigating whether L. acidophilus, as part of the gut flora or taken as a probiotic, could play a role in supporting certain cancer therapies or even in preventing the development of cancer. However, all of this research has been in animals or cells thus far, and there is no clinical evidence to recommend L. acidophilus for this purpose.
Daily oral administration of L. acidophilus suppressed colon tumor incidence, tumor multiplicity, and reduced tumor size in mice .
Oral administration of L. acidophilus increased survival , decreased tumor growth and increased lymphocyte proliferation in mice with breast tumors .
L. acidophilus reduced tumor volume growth by 50.3 %, reduced the severity of colonic carcinogenesis, and enhanced cancer cell death in mice .
L. acidophilus decreased carcinogenic changes in the colon in rats .
L. acidophilus alters the cytokine production in tumor-bearing mice into a Th1 protective pattern, favorable to anti-tumor immunity .
L. acidophilus is also being investigated directly against gastric carcinoma, colon carcinoma, and breast cancer cells [78, 79].
Mechanism of Effect
Researchers have conducted a number of cell and animal studies to investigate the effect of L. acidophilus on a biochemical level. Here are some of their findings:
- Enhanced natural killer cell (NK) activity [54, 80].
- Decreased NF-κB [81, 28] and increases IL-8 .
- In influenza, L. acidophilus deotaxin, CSF1, IL-1β, RANTES, and IFN -α in the lung, and increased IL-17 in the intestine .
- Upregulated IL-1α, IL-1β, CCL2, and CCL20, and activated TLR2 in intestinal epithelial cells .
- Increased the secretion of IFNγ from T-cells in fatigued athletes .
- Suppressed Th2-dominant inflammation by activating regulatory T cells and Th1 helper T cells .
- Increased TGF-β [32, 81, 55, 30].
- Decreased NF-κB activity [81, 59].
- Suppressed IL-17 and IL-23 , TNF-α, IL-8, MIR21 [81,59], IL-6, and IL-12 .
- Both increased and decreased IL-12 [55, 30].
- Stimulated IL-10 .
- Induced intestinal IgA .
- Inhibited iNOS and PTGS-2 .
- Suppressee IgE [33, 35], IL-4 [84,85], IL-17A and IL-6 [40,40].
- Increased TGF-β and IgA [84, 40, 40, 41].
- Both increased and decreased IFN-γ [84, 85] and IL-10 [40, 41].
- Increased CD25 and FOXP3  and decreased RORγt .
- Significantly increased CD4(+)CD25(+)Foxp3(+) T cells , decreased the proliferation of CD4(+) T cells stimulated with antigen, and killed antigen-stimulated T cells .
- Improved peritoneal macrophage functions, stimulated NO and IL-6, and inhibited PGE2 .
- Improved lymphocyte functions and stimulated IL-2 .
- Increased catalase (CAT) activity .
- Reversed age-related decline in PPARα, SMP-30, and klotho .
- Altered cytokine production in a tumor into a Th1 protective pattern, favorable to anti-tumor immunity [75, 74].
- Inhibited the expressions of genes involved in tumor angiogenesis and survival, VEGF and HIF-1α .
- Upregulated TIMP-3, HIF-2α, HO-1, and PAI-1 .
- Increased IFN-γ and decreased IL-4 .
L. acidophilus is generally well tolerated. However, the use of probiotics should be avoided in patients with organ failure, immunocompromised status, and dysfunctional gut barrier mechanisms, where it can lead to infections .
To ensure that probiotics are safe for you, and to avoid any adverse effects, talk to your doctor before starting any new probiotic supplements.