Stevia and Lyme Disease: What a 2015 Lab Study Found About Borrelia burgdorferi

Background: Why Lyme Disease Is Difficult to Treat. Lyme disease is caused by Borrelia burgdorferi, a spiral-shaped bacterium (spirochaete) transmitted through the bite of infected blacklegged ticks. Standard treatment with antibiotics such as doxycycline, amoxicillin, or cefuroxime is effective when the infection is caught early. However, a significant proportion of patients continue to experience symptoms after completing antibiotic treatment — a condition sometimes called Post-Treatment Lyme Disease Syndrome (PTLDS). One proposed explanation for treatment resistance involves the ability of Borrelia to exist in multiple morphological forms: the free-swimming spirochaete form (the standard form targeted by antibiotics), round body forms (also called cysts or persister cells, which are metabolically dormant and antibiotic-tolerant), and biofilm forms (aggregates of bacteria encased in a protective matrix that are highly resistant to both antibiotics and the immune system). Standard antibiotics are effective against spirochaetes but have limited activity against round bodies and biofilms. This has driven interest in natural compounds that might target all three forms simultaneously.

The 2015 University of New Haven Study. The study was conducted by Eva Sapi and colleagues at the University of New Haven and published in the European Journal of Microbiology and Immunology in 2015 (Theophilus et al., 2015). The researchers tested a commercially available whole-leaf stevia extract (not purified stevioside or rebaudioside A, the isolated sweetener compounds) against Borrelia burgdorferi in laboratory cell cultures. They compared the stevia extract to three antibiotics commonly used for Lyme disease: doxycycline, cefoperazone, and daptomycin, as well as combinations of these antibiotics. The stevia extract was tested against all three morphological forms of Borrelia: the spirochaete form, round body forms, and biofilm forms. The key finding was that the whole-leaf stevia extract significantly reduced the viability of Borrelia in all three forms. Against biofilms — the most treatment-resistant form — the stevia extract outperformed all three individual antibiotics and performed comparably to or better than antibiotic combinations. Against round body forms, the stevia extract again outperformed individual antibiotics. Against spirochaetes, the stevia extract was effective, though doxycycline was also effective in this form.

What Made the Whole-Leaf Extract Different. A critical detail in the study is that the researchers used a whole-leaf stevia extract, not the purified stevioside or rebaudioside A compounds used as sweeteners. When they tested purified stevioside alone, it showed significantly less antimicrobial activity than the whole-leaf extract. This suggests that the antimicrobial effect is not attributable to the well-known sweet glycosides alone, but to other compounds present in the whole leaf — potentially including polyphenols, flavonoids, and other phytochemicals that are removed during the purification process used to produce commercial stevia sweeteners. This distinction matters practically: stevia sweetener products (packets, drops, tablets) are not the same as the whole-leaf extract used in the study and would not be expected to produce the same effects.

Evidence Tier and Significant Limitations. This study is rated Tier D (preliminary/exploratory) on the Coeheal evidence hierarchy. The reasons are important to understand. It is a single in vitro (cell culture) study. In vitro studies test compounds in laboratory conditions that do not replicate the complexity of a living organism. Many compounds that kill bacteria in a petri dish fail to do so in the human body, because they may be poorly absorbed, rapidly metabolised, unable to reach the site of infection at effective concentrations, or toxic at the doses required. There has been no human clinical trial of stevia extract for Lyme disease. There has been no animal study. The study has not been independently replicated. The dose used in the study has not been established as safe or effective in humans. The researchers themselves noted that the findings were preliminary and that further research — including in vivo (animal) and clinical studies — would be needed before any clinical conclusions could be drawn. The study should be understood as hypothesis-generating: it identifies a potentially interesting compound worthy of further investigation, not as evidence that stevia treats Lyme disease in humans.

What This Means Practically. For people with Lyme disease or PTLDS, this study does not provide a basis for replacing or discontinuing prescribed antibiotic treatment. Lyme disease is a serious bacterial infection, and the consequences of undertreated infection — including neurological, cardiac, and joint complications — are well-documented. The study does provide a rationale for further research into whole-leaf stevia extract as a potential adjunct or alternative therapy, and it adds to a growing body of interest in plant-derived compounds with activity against Borrelia. If you are interested in incorporating stevia into your diet for its general health properties (it is a zero-calorie natural sweetener with a reasonable safety profile at culinary doses), that is a separate question from its potential antimicrobial use. Therapeutic use of concentrated whole-leaf stevia extract for Lyme disease is not currently supported by clinical evidence and should only be considered under the supervision of a qualified healthcare provider experienced in Lyme disease management.