The human body is host to a community of microorganisms, known as the human microbiome. This population includes bacteria, viruses, fungi, and archaea that inhabit nearly every part of our bodies. These microbes are active participants in our biology, and scientific understanding has grown, revealing the connections between them and our overall health.
Our Microbial Inhabitants
The human microbiome is a vast collection of microorganisms, with bacterial cells estimated to be as numerous as human cells in the body, making them the most abundant members. These microbes form distinct communities at different sites on and in the body, each with a unique composition tailored to its specific environment.
The most densely populated microbial habitat is the gastrointestinal tract, where trillions of microbes reside, particularly in the large intestine. Other significant microbial communities are found in the oral cavity on surfaces like the teeth, tongue, and gums. The skin also hosts a variety of microbes, with the composition varying depending on the location’s moisture, temperature, and oil content.
Distinct microbial ecosystems also exist in the respiratory tract, including the nasal passages and lungs, and the urogenital tract. The specific makeup of the microbiome in each of these locations differs significantly. For instance, the microbes thriving in the acidic environment of the stomach are vastly different from those on the neutral-pH environment of the skin.
Essential Functions of Your Microbiome
The microbiome performs many functions beneficial to human health, with a primary role in digestion and metabolism. Gut microbes possess enzymes capable of breaking down complex carbohydrates, such as dietary fiber, that human cells cannot digest. This process extracts additional nutrients from our food and produces beneficial compounds called short-chain fatty acids (SCFAs), which serve as an energy source for intestinal cells.
The microbiome is also involved in the development and regulation of the immune system. From birth, these microbes help “train” our immune cells to differentiate between harmless substances and dangerous pathogens. This education prevents both infections and inappropriate immune responses, such as allergies. A healthy microbial community also acts as a protective barrier, competing with invading pathogens for space and resources and producing antimicrobial substances that inhibit the growth of harmful bacteria.
The synthesis of nutrients is another function of our microbial partners. Gut bacteria produce certain vitamins that our bodies cannot make, most notably vitamin K, which is required for blood clotting, and several B vitamins, including biotin and folate. The microbiome also maintains the integrity of the gut lining, a physical barrier that prevents harmful substances and microbes from entering the bloodstream.
Influences on Your Microbial Ecosystem
The composition of an individual’s microbiome is shaped by many factors throughout life, starting from the moment of birth. The mode of delivery is an early influence; infants born vaginally acquire a microbial community resembling their mother’s vaginal microbiome, while those born via Cesarean section are initially colonized by microbes from the skin and the hospital environment. Infant feeding methods also play a part, with breastfed and formula-fed babies developing different gut microbial patterns.
Diet is a powerful tool for shaping the microbiome in adults. A diet rich in fiber from fruits, vegetables, and whole grains provides fuel for beneficial gut bacteria, promoting their growth. Conversely, diets high in processed foods, sugar, and certain fats can favor the growth of less beneficial microbes. The use of medications, particularly antibiotics, can have a significant impact, as these drugs often eliminate both harmful and beneficial bacteria.
Lifestyle and environmental exposures also contribute to the diversity and composition of our microbiome. Factors such as chronic stress, sleep patterns, and physical activity levels influence microbial balance. A person’s location, exposure to the natural environment, and contact with pets can introduce new microbes and alter existing communities. An individual’s genetics also plays a role, influencing which microbes are more likely to thrive in their body.
When Our Microbiome is Disrupted
An imbalance in the composition and function of the microbial communities in our body is a state known as dysbiosis. This disruption can occur when there is a loss of beneficial microbes, an overgrowth of potentially harmful ones, or a general reduction in microbial diversity.
Dysbiosis is linked to many health conditions, especially in the gastrointestinal tract. For example, alterations in the gut microbiome are observed in individuals with inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). These changes can contribute to chronic inflammation and their symptoms.
A disrupted microbiome’s consequences can extend beyond the gut. Research links dysbiosis and various metabolic conditions, including obesity and type 2 diabetes. Imbalances in gut bacteria can affect how the body stores fat, regulates blood sugar, and responds to hormones involved in hunger. Evidence also points to a connection between the gut microbiome and the brain, linking dysbiosis to conditions like anxiety and depression.