According to Gram Research analysis, cold exposure damages heart health by altering gut bacteria composition, which increases an amino acid called leucine that impairs immune cells’ ability to clean up dead cells in blood vessels. A 2026 study found that supplementing with Lactobacillus johnsonii bacteria reversed this process in mice, suggesting that maintaining healthy gut bacteria during winter may help prevent cold-related heart disease.
A groundbreaking 2026 study reveals how cold exposure triggers harmful changes in gut bacteria, leading to increased risk of heart disease. Researchers discovered that cold temperatures cause the gut microbiota to produce more of an amino acid called leucine, which damages the immune system’s ability to clean up dead cells in blood vessels. This buildup causes inflammation and unstable plaques that can lead to heart attacks. The good news: supplementing with a beneficial bacteria called Lactobacillus johnsonii reversed these harmful effects in mice. This research suggests that protecting or restoring healthy gut bacteria during winter months could help prevent cold-related heart disease.
Key Statistics
A 2026 research article in the Journal of Translational Medicine found that cold exposure caused gut microbiota dysbiosis and elevated circulating leucine levels, which suppressed the Zic2-Gas6 signaling pathway in macrophages, leading to impaired clearance of apoptotic cells and increased atherosclerotic plaque instability.
Supplementation with Lactobacillus johnsonii normalized circulating leucine levels, restored Zic2-Gas6 signaling, enhanced macrophage efferocytosis, and attenuated atherosclerotic plaque progression in cold-exposed mice according to the 2026 study.
Direct leucine supplementation in mice recapitulated all the harmful effects of cold exposure on plaque development and instability, demonstrating that the amino acid is the key mechanistic link between environmental stress and atherosclerosis progression.
The Quick Take
- What they studied: How cold weather affects the gut bacteria and whether changes in bacteria contribute to heart disease development
- Who participated: Laboratory mice genetically prone to heart disease, fed a Western-style diet high in fat and processed foods, exposed to cold temperatures
- Key finding: Cold exposure changed the composition of gut bacteria and increased levels of leucine (an amino acid), which impaired the immune system’s ability to clean up damaged cells in blood vessels, leading to larger and more unstable heart plaques
- What it means for you: People living in cold climates may face increased heart disease risk through gut bacteria changes. Consuming foods with beneficial bacteria or specific probiotic strains might help protect heart health during winter, though human studies are needed to confirm this
The Research Details
Researchers used mice that were genetically engineered to develop heart disease, similar to how some humans are predisposed to atherosclerosis. They exposed these mice to cold temperatures while feeding them a Western diet (high in fat and processed foods) to mimic real-world conditions. The team then transferred gut bacteria from cold-exposed mice to other mice to test whether the bacteria alone caused the heart problems. They also gave some mice a beneficial bacteria called Lactobacillus johnsonii to see if it could reverse the damage. Throughout the study, they measured changes in gut bacteria composition, amino acid levels in the blood, immune cell function, and the size and stability of heart plaques.
The researchers used advanced laboratory techniques called multi-omics analysis, which allowed them to simultaneously examine thousands of genes, proteins, and metabolites to understand the complete picture of what was happening. This comprehensive approach revealed not just that bacteria changed, but exactly how those changes led to heart disease through a specific chain of molecular events.
This type of mechanistic study is important because it doesn’t just show that two things are connected—it explains the step-by-step biological pathway linking cold exposure, gut bacteria, and heart disease. This level of detail helps scientists develop targeted treatments.
Understanding the specific mechanism linking cold exposure to heart disease through gut bacteria opens new treatment possibilities. Rather than treating heart disease after it develops, doctors could potentially prevent it by maintaining healthy gut bacteria composition, especially in people living in cold climates. The discovery that a single beneficial bacterium (Lactobacillus johnsonii) could reverse the harmful effects suggests a practical, non-drug intervention.
This study used rigorous scientific methods including controlled laboratory conditions, multiple experimental approaches (bacterial transplants, genetic analysis, cellular assays), and both disease-promoting and disease-preventing interventions to test cause-and-effect relationships. The research was published in a peer-reviewed journal, meaning other experts reviewed it before publication. However, the study was conducted in mice, not humans, so results may not directly apply to people. The specific genetic background of the mice and the artificial cold exposure conditions may not perfectly mirror real-world human scenarios.
What the Results Show
Cold exposure caused significant changes in the composition of gut bacteria in the mice, with certain beneficial bacteria becoming depleted while potentially harmful bacteria increased. Simultaneously, the researchers observed elevated levels of leucine (an amino acid) in the bloodstream of cold-exposed mice. When they transferred bacteria from cold-exposed mice to other mice, those recipient mice also developed elevated leucine levels and heart disease progression, proving the bacteria were responsible for the effect.
The mechanism worked through a specific biological pathway: high leucine levels suppressed a gene called Zic2 in immune cells called macrophages. This suppression reduced production of a protein called Gas6, which normally helps macrophages clean up dead and dying cells in blood vessel walls. Without adequate Gas6, macrophages couldn’t efficiently remove these dead cells, leading to accumulation of cellular debris, increased inflammation, and formation of unstable plaques that are prone to rupture and cause heart attacks.
When researchers gave mice the beneficial bacterium Lactobacillus johnsonii, it reversed all these harmful effects: leucine levels normalized, Zic2-Gas6 signaling was restored, macrophages regained their cleaning ability, and plaque progression slowed. Conversely, when they directly supplemented mice with extra leucine, it recreated all the harmful effects of cold exposure, confirming that leucine was the key culprit.
The study revealed that cold exposure triggered broader immune system dysfunction beyond just the macrophage cleaning problem. Vascular inflammation increased significantly in cold-exposed mice, and the plaques that formed were structurally weaker and more prone to rupture—characteristics that make heart attacks more likely. The research also showed that the gut bacteria changes were not random but followed specific patterns, with cold-loving bacteria increasing while heat-adapted bacteria decreased, suggesting the microbiota was responding directly to temperature changes.
Previous research established that cold exposure increases heart attack risk and that gut bacteria influence cardiovascular health, but the specific connection between these two observations was unknown. This study fills that gap by identifying the exact molecular pathway. The finding that a single amino acid (leucine) could drive the entire disease process is novel and unexpected, as most researchers focused on other bacterial metabolites. The role of Lactobacillus johnsonii in preventing cold-induced heart disease is particularly significant because this bacterium is already recognized as beneficial for digestive health, suggesting it may have multiple protective roles in the body.
The most important limitation is that this research was conducted in mice, not humans. Mice have different body sizes, metabolic rates, and lifespans, so results may not directly translate to people. The mice were genetically engineered to develop heart disease, which may make them more susceptible to the effects than average humans. The cold exposure in the laboratory was controlled and continuous, whereas humans experience variable cold exposure and can use clothing and heating to protect themselves. The study used a Western diet in mice, which may not perfectly match human diets. Finally, the sample size of mice used in each experiment was not specified in the abstract, making it difficult to assess statistical power. Human clinical trials would be necessary to confirm whether Lactobacillus johnsonii supplementation actually prevents cold-induced heart disease in people.
The Bottom Line
Based on this research, people living in cold climates or experiencing seasonal temperature drops may benefit from maintaining healthy gut bacteria through diet and possibly probiotic supplementation. Eating fermented foods (yogurt, sauerkraut, kimchi) and foods high in fiber supports beneficial bacteria growth. While Lactobacillus johnsonii supplementation showed promise in mice, human studies are needed before recommending it as a preventive treatment. People with existing heart disease or family history of heart disease should discuss cold-weather precautions with their doctor. Confidence level: Moderate—the mechanism is well-demonstrated in mice, but human evidence is lacking.
This research is particularly relevant for people living in cold climates, those with family history of heart disease, older adults (who have higher heart disease risk), and people with existing cardiovascular conditions. Anyone taking antibiotics that disrupt gut bacteria should be aware that this may temporarily increase their vulnerability to cold-induced heart disease. People with healthy hearts living in warm climates have lower immediate risk, though maintaining good gut health is beneficial for overall health regardless. Pregnant women and children should consult healthcare providers before taking probiotics.
In the mouse studies, changes in gut bacteria composition and leucine levels occurred within days of cold exposure, while plaque progression took weeks to become significant. In humans, similar changes might take longer due to our larger body size and slower metabolism. Benefits from probiotic supplementation, if they occur, would likely take several weeks to months to become apparent, as it takes time for beneficial bacteria to establish themselves in the gut and influence systemic metabolism.
Frequently Asked Questions
Does cold weather actually increase heart attack risk?
Research shows cold exposure accelerates atherosclerosis and plaque instability through gut bacteria changes that increase an amino acid called leucine. A 2026 study demonstrated this mechanism in mice, suggesting cold climates may increase cardiovascular risk, particularly in people with existing heart disease.
Can probiotics help prevent heart disease in winter?
A 2026 study found that Lactobacillus johnsonii reversed cold-induced heart disease in mice by normalizing leucine levels and restoring immune cell function. While promising, human clinical trials are needed to confirm whether probiotic supplementation prevents heart disease in people living in cold climates.
What foods should I eat to maintain healthy gut bacteria in cold weather?
Fermented foods like yogurt with live cultures, sauerkraut, kimchi, and kefir support beneficial bacteria growth. High-fiber foods (vegetables, whole grains, legumes) also feed good bacteria. Research suggests maintaining diverse gut bacteria may help protect cardiovascular health during cold exposure.
How does gut bacteria affect heart health?
Gut bacteria produce metabolites like leucine that enter the bloodstream and influence immune cell function throughout the body. A 2026 study showed that cold-induced changes in bacteria increase leucine, which impairs macrophages’ ability to clean up dead cells in blood vessels, promoting heart disease.
Is this research applicable to humans or just mice?
The study was conducted in genetically engineered mice, so results haven’t been confirmed in humans yet. The mechanism is well-demonstrated in mice, but human clinical trials are needed to determine whether Lactobacillus johnsonii supplementation actually prevents cold-induced heart disease in people.
Want to Apply This Research?
- Track daily temperature exposure (time spent in cold environments) and correlate with cardiovascular symptoms like chest discomfort, shortness of breath, or unusual fatigue. Users can log outdoor time, heating system usage, and seasonal changes to identify personal patterns.
- Users can set reminders to consume probiotic-rich foods during winter months (fermented foods, yogurt with live cultures) and track intake. The app could suggest seasonal dietary adjustments and provide cold-weather heart health tips like staying warm and maintaining exercise routines indoors.
- Implement long-term tracking of heart health markers (resting heart rate, blood pressure if user has a monitor) alongside seasonal and temperature data. Users could log any cardiovascular symptoms and correlate them with cold exposure patterns and dietary probiotic intake to identify personal relationships between these factors.
This research was conducted in laboratory mice and has not been confirmed in humans. The findings suggest potential mechanisms linking cold exposure to heart disease through gut bacteria, but individual results may vary significantly. This information should not replace professional medical advice. People with existing heart disease, those at high risk for cardiovascular events, or anyone considering probiotic supplementation should consult their healthcare provider before making dietary changes or starting supplements. Cold exposure recommendations should be discussed with a doctor, particularly for individuals with known cardiovascular conditions. Probiotics are not regulated by the FDA in the same way as medications, and quality and effectiveness vary between products.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.