In 1918, in the midst of the influenza pandemic, nurses around the world cared for entire cities – often using simple methods, hygiene, and nutrition. One of them was the British nurse and early public health advocate Florence Nightingale, who had already demonstrated how systematic care and clean food can curb infections. Today, research focuses on a new lever: beneficial microorganisms in foods and supplements. The idea is ancient – fermented foods have existed for thousands of years – but it is only modern microbiome science that shows how probiotics could specifically modulate our immune response. For high performers, this is an invitation: do not leave immune protection to chance, but shape it with science.

Probiotics are probioticsliving microorganisms that provide health benefits when consumed in adequate amounts, often strains from the groups Lactobacilluslactic acid bacteria that ferment sugars into lactic acid and Bifidobacteriumgut inhabitants that break down fibers into useful metabolites. Prebiotics are prebioticsindigestible fibers that selectively feed beneficial gut bacteria. Combined, they are referred to as synbioticsa mixture of probiotics and prebiotics with a synergistic effect. Why the immune system can benefit from this: a large part of our immune cells is located in the gut. Microbial metabolites such as short-chain fatty acids (SCFA)e.g., butyrate; fuel for gut cells, anti-inflammatory stabilize the gut barrier, influence signaling pathways of the innate and adaptive defenses, and promote a balanced response to pathogens rather than chronic inflammation. Important: Effects are strain-specific – not every “probiotic” works the same ^[1].

Regularly fermented foods such as yogurt, kefir, or kimchi provide microbes and bioactive metabolites that review articles indicate strengthen the epithelial barrier, dampen inflammation signals, and are associated with fewer infections and better metabolic health ^{[2] [3]}. In studies, defined probiotic vaccinations of the gut show measurable immune effects: more active natural killer cells, improved function of macrophages, and a stronger T- and B-cell response – all building blocks for a more efficient defense without overreaction ^{[4] [1]}. It becomes clinically relevant in respiratory infections: In a randomized, placebo-controlled study, children with recurrent respiratory infections experienced fewer and shorter episodes under certain Bifidobacterium and Lactobacillus strains; simultaneously, their gut microbiota normalized – an indication of the gut-lung axis ^[5]. Synbiotics partially enhance these effects by optimizing barrier, microbiota, and SCFA production simultaneously ^[6].

A recent review classifies probiotics as immune-modulating tools: Lactic bacteria and yeasts such as Saccharomyces boulardii interact with immune cells in the lamina propria through microbial metabolites and can harmonize both innate and adaptive responses. The authors emphasize: efficacy is strain- and dose-dependent; documented benefits range from infection prophylaxis to the reduction of gastrointestinal inflammation ^[1]. It becomes more precise in a mouse model and cell studies on Bifidobacterium bifidum BGN4: This strain enhanced NK cell cytotoxicity, activated macrophages (among others via MAPK/NF-κB), and prevented the decline of important immune parameters under immunosuppression – a mechanistic proof of immune-boosting potential, supporting the selection of defined strains ^[4]. Clinical relevance is shown by data from a double-blind study in children with recurring respiratory infections: Daily administration of Bifidobacterium animalis subsp. lactis XLTG11 and Lactobacillus plantarum CCFM8661 reduced the number and duration of new episodes, modified the gut flora towards beneficial taxa, and stabilized humoral markers – without safety concerns. This supports a strain-specific, everyday prevention strategy ^[5]. Additionally, a synbiotics study indicates that the combination of selected prebiotics and Lacticaseibacillus rhamnosus not only reduces inflammatory mediators but also enhances barrier and SCFA production, thereby effectively utilizing the “gut-metabolite-immune system” axis ^[6].

- Incorporate probiotic-rich foods daily: natural yogurt, kefir, fermented vegetables (e.g., kimchi, sauerkraut). Start with one serving per day and prefer products with active cultures and low sugar. This will strengthen barrier function and microbiome diversity ^{[2] [3]}.
- Use a probiotic supplement with clearly declared strains (e.g., Lactobacillus and Bifidobacterium species) and sufficient CFU count. Take it daily for at least 8–12 weeks to give the immune system time to adjust ^{[1] [4]}.
- Consider synbiotics that combine probiotics with prebiotic fibers. Look for formulations with proven effects on SCFA and barrier health; beneficial in times of high stress, travel, or after antibiotics ^[6].
- Specifically check for strains with evidence for respiratory infections – such as B. animalis subsp. lactis XLTG11 and L. plantarum CCFM8661 – especially during infection seasons or increased exposure. Consult pediatricians and family doctors for use in children ^[5].

Probiotics are not a panacea, but a precise lever: defined strains and fermented foods can measurably enhance your immune resilience. Next step: daily a portion of fermented food, test a transparently labeled probiotic for 8–12 weeks, and – if necessary – switch to an evidence-based synbiotic.