Your intestines are home to many different kinds of bacteria (and some non-bacterial organisms as well). Together they’re called the “gut microbiome.” They come from the food you eat – and whatever else gets into your mouth. Bacteria start colonizing your gut at birth. Your gut microbiome aids in digestion and produces vitamins and other compounds that affect your health. It seems to play a role in many other health-related functions, including metabolism, cardiac health and mood. New evidence shows that the bacteria in our gut also interact with our immune systems, and might even influence the body’s immune reaction to vaccines.
The link between your gut and your immune system
We are still learning how gut bacteria and the immune system interact. Research suggests that the interaction evolved over time to manage the balance between reacting to harmful pathogens and tolerating non-harmful organisms. You want your immune system to react to the pathogens that can make you sick, while letting the beneficial bacteria living in your gut go about their business.
We are still learning what a healthy gut microbiome looks like. Evidence suggests that a balanced and diverse microbiome might contribute to better health overall, and a less diverse or less balanced microbiome can have a negative impact on health.
A review article from 2014 suggests that the overuse of antibiotics, changes in diets and the elimination of beneficial organisms that work with bacteria in high income countries may have resulted in gut microbiomes that lack the resilience and diversity of functions required to establish balanced immune responses.
That matters because having less diverse gut bacteria has been linked to inflammatory bowel diseases and the increase in autoimmune diseases in developed countries. For instance, a 2013 study found that children living in Bangladesh have more diverse gut microbiomes than children from the United States. Researchers suggest that dietary differences – with children in the US eating more animal fats and protein – are a factor.
Unhealthy gut bacteria can reduce the effectiveness of vaccines
Scientists have started examining the interactions between gut bacteria and responses to vaccines. A recent review article concluded that the composition of your gut microbiome can influence whether a vaccine has an effect in your body.
Unhealthy gut microbiome composition (or “dysbiosis”) can lead to inflammation. And that means more bacterial cells pass through the damaged lining of the gut, which stimulates further immune system responses. This is called “leaky gut.” Vaccines may not be as effective because the immune system is already busy dealing with these bacterial cells “leaking” through the gut. On the other hand, having a diverse and “healthy” gut microbiome, and thus no gut inflammation and “leakiness,” might allow a person’s immune system to focus on responding to the vaccine effectively.
Recent research has also found that the effectiveness of the seasonal flu shot could be enhanced by intestinal bacteria. The immune system detects specific proteins from the bacteria, and this detection seems to increase the immune system’s response to the flu vaccine. Then your body has an easier time mounting an immune response if you are exposed to the real flu virus.
Gut bacteria aren’t the only thing influencing your immune system. Science is nowhere near being able to tell you which bacteria will always cause what immune system responses. And keep in mind that your gut bacteria are by no means the only factor affecting your immune system. Nutrition, age, sex, genetics and the kinds of pathogens you’ve been exposed to can all have an effect.
Scientists don’t yet know exactly what a health-beneficial gut microbiome looks like, though recent research points to the fact that the specific biochemical functions that different bacteria can carry out are more important than the particular species present in your gut.
Maintaining a healthy microbiome
Currently, researchers believe the best way to establish and maintain a healthy gut microbiome is to get enough sleep and exercise, eat healthy meals that include lots of fruits and vegetables, avoid chronic and excessive stress and not to drink too much. You can also help maintain healthy gut bacteria by taking antibiotics only when they are necessary.