Kefir-derived bacteria may slow aging in mice, study suggests

A laboratory study in Japan suggests that a heat-inactivated strain of lactic acid bacteria isolated from kefir may help slow aging-related changes in the immune system, at least in mice. Researchers at Shinshu University fed elderly mice a specific LAB strain, Lentilactobacillus kefiri YRC2606, over eight weeks and then evaluated immune function and organ condition. The study found that mice receiving YRC2606 exhibited fewer age-related alterations in key organs, including the thymus and liver, and showed lower levels of inflammatory markers. In addition, the treatment correlated with reduced expression of proteins that typically halt cell division, a process linked to tissue aging. The work represents a first-of-its-kind look at kefir-derived bacteria’s potential to modulate aging processes, at least in an animal model.

Lead author Hiroka Sasahara summarized the finding, saying the LAB strain could be useful for addressing age-associated diseases, for example, as an ingredient in functional foods or dietary supplements designed to maintain immune function in older adults. “YRC2606 will be useful for the treatment of age-associated diseases, for example, as an ingredient in functional foods or dietary supplements designed to maintain immune function in older adults,” she said in a statement. The researchers noted that preserving immune function is integral to maintaining physical performance and independence as people age, potentially reducing susceptibility to infections and other health declines.

Kefir is a tangy, fermented dairy drink long praised for gut health and immune support. It contains live cultures of lactic acid bacteria and yeasts, along with nutrients that vary by producer but commonly include protein, calcium, phosphorus, magnesium, and several B vitamins. Probiotics in kefir—such as Lactobacillus kefiri—are believed to help combat harmful bacteria, support digestion, and potentially influence metabolic and inflammatory processes. While the study focused on a single LAB strain isolated from kefir, experts say probiotic foods have demonstrated a range of health effects in humans, from digestion and weight management to heart health and mental well-being through gut microbiome balance.

In humans, aging is associated with a gradual decline in immune competence, known as immunosenescence, and a chronic, low-level inflammatory state that can contribute to a host of age-related diseases. The Shinshu University study fed older mice the heat-inactivated YRC2606 strain, meaning the bacteria were not alive to proliferate in the gut. The researchers observed reduced inflammation and a slowdown in the cellular aging process within the thymus and liver, both of which are critical for immune function and metabolic regulation. The team also noted lower activity of cell-cycle inhibitors—proteins that stop cells from dividing—which, when persistent, are linked to tissue aging and functional decline. The combination of these effects points to a potentially broader role for kefir-associated bacteria in supporting immune resilience in aging organisms.

The study’s findings, while promising, are limited to an animal model and do not yet translate to human aging or disease prevention. Sasahara emphasized that further research is needed to determine whether similar effects would occur in people, and whether a heat-inactivated, kefir-derived bacterial component could be developed into safe, effective foods or supplements for older adults. “If future work confirms these results in humans, YRC2606 could become an ingredient in products designed to preserve immune function and to maintain physical capabilities in aging populations,” she noted.

The aging demographic context adds urgency to such work. The United States and many other countries are experiencing growing numbers of older adults as birth rates decline and life expectancy rises. Analysts have warned that the coming decade could see older Americans outnumbering children for the first time in U.S. history, a shift that places increasing importance on interventions that support healthy aging, independence, and quality of life. While kefir’s benefits for digestion and immune health are widely discussed, the new study introduces the possibility that kefir-derived bacteria could also influence aging processes at the cellular level, at least in animal models.

Beyond potential aging implications, kefir remains a nutrient-dense beverage. One cup typically provides about nine grams of protein and more than a third of an adult’s daily calcium, along with phosphorus, magnesium, and vitamins B12, B2, D, and K2. The probiotic content—comprising various Lactobacillus strains and yeasts—has been associated with improved gut microbiota balance and a range of health outcomes, including digestion, weight management, and heart health. In addition, some kefir probiotics have shown the ability to inhibit growth of certain harmful bacteria such as Salmonella and Escherichia coli, though the exact benefits can vary by product and individual.

As with any probiotic or functional food, there are caveats. Some people may experience gas, bloating, or other digestive side effects as their gut microbiome adjusts to new microbes. Individuals taking immunosuppressants or with compromised immune systems should consult a healthcare professional before increasing kefir intake, since live bacteria and yeasts in probiotic foods could carry infection risks in those scenarios. Experts caution that heat-inactivated or non-viable bacterial components may differ in effect from live cultures, and results seen in mice do not guarantee similar outcomes in humans. Researchers say human clinical trials will be essential to determine safety, optimal dosages, and real-world benefits if kefir-derived components are pursued as therapeutic or preventive tools for aging.

In the meantime, kefir can be consumed as part of a balanced diet for those who tolerate dairy products and do not have conditions that contraindicate probiotic beverages. Its potential anti-aging implications remain an active area of inquiry, and scientists stress that any practical application would require rigorous, replicated studies in humans before health claims could be substantiated.