Clinical Research - Probiotics
Clinical Research

Probiotics: What the Science Says


The scientific studies described on this website were conducted by independent researchers, and presented for educational purpose only. The views expressed in the studies do not reflect those of the owner of this website. The subject products of the studies may be classified as dietary supplements in the United States. Those dietary supplements are not intended to diagnose, treat, cure or prevent any disease.

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Can probiotics reduce hospital-acquired infection?

As we age, the gut microbiotic community changes. Specifically, levels of Bifidobacterium and Lactobacillus bacteria both decline, which is problematic since they’re known to maintain gut health, immunity and healthy inflammation. Could supplementation restore these levels? Yes, according to research published in Journal of the American College of Nutrition.1

Researchers supplemented older participants, about age 70, with a probiotic mixture (including Lactobacillus gasseri, Bifidobacterium bifidum and Bifidobacterium longum) or placebo twice daily for three weeks. They measured CD4 cells, a marker for immune health, at the beginning and end of the treatment period. What they found was that the supplement group was able to maintain their CD4 levels, while the placebo group’s levels decreased. The supplement group also demonstrated a healthier inflammatory response.

In all, researchers say that supplementation changed the microbial communities of participants to the extent that theirs more closely resembled those of younger people.

1. J Am Coll Nutr. 2015;34(6):459-69.

Can probiotics reduce hospital-acquired infection?

Despite hospitals’ best efforts, people can still get sick while in their care. Researchers wanted to know if probiotics may be able to support a patient’s immune system to avoid hospital-acquired infections and maybe even shorten patients’ hospital stays.

Researchers recruited 50 patients with either blood diseases or cancer, who were also predicted to have hospital stays of at least three days. Participants were supplemented with either probiotics (1.5 billion cells of Lactobacillus acidophilus, Bifidobacterium bifidus and Bifidobacterium longus) or placebo once daily for the duration of their hospital stay. Ultimately, researchers found that supplementing with probiotics did impact the number of hospital-acquired infections in these patients, by reducing the risk of infection by 20%, even if the lengths of their stays were similar.

Despite the lack of difference in the duration of hospital stays, the decrease in occurrence of hospital-acquired infection in the probiotics group implies a better outcome, since patients can proceed to definitive treatment earlier and there is lesser need for antibiotics needed to treat nosocomial infection. Findings were published in PIDSP Journal.2

2. PIDSP J. 2005;9(2):12-18.

Can probiotics help allergy symptoms?

The changing of seasons often brings an unwelcome intruder: allergies. From sneezing and post-nasal drip to congestion and runny noses, sinus troubles abound. Researchers wondered if probiotics could help ease the symptoms of sufferers throughout the allergy season. The short answer is, yes. Their results were published in The American Journal of Clinical Nutrition.3

Researchers at the University of Florida recruited 173 participants with seasonal allergies to receive either a probiotic (Lactobacillus gasseri KS-13, Bifidobacterium bifidum G9-1 and B. longum MM-2) or placebo during eight weeks of the spring allergy season. Though the supplement group self-reported an ease in symptoms, their blood samples didn’t reveal significant changes in allergy markers. So, while the mechanism of action is still unclear, the study concluded that the probiotics did help increase quality of life for allergy sufferers.

3. Am J Clin Nutr. 2017;105(3):758-67.

Can probiotics ease the common cold?

During the course of two winter and spring periods, researchers enrolled over 450 participants to receive either probiotics or placebo for three months in a double-blind, randomized, placebo- controlled trial. If participants caught a cold, they recorded their symptoms daily.

As it turns out, total cold symptoms, cold durations and number of days with a fever were lower in the probiotic-treated group than in the placebo group. In all, probiotics seemed to strengthen immune system function during the common cold season, reported the study published in Clinical Nutrition.4

4. Clin Nutr. 2005;24(4):481-91.