Unravelling the gut microbiome BAD BUGS and brain health
You may remember the word ‘biome’ from science class – it’s a habitat such as a desert or grassland, based on local climate and plant life. Your body contains its own little worlds, unique habitats of trillions of tiny beasties – viruses, fungi, bacteria and other microorganisms living on you and inside you. In humans, microbes gather in these places on the skin, in the nose and in the gastrointestinal tract (also known as the gut).
With the help of everyday people, researchers have uncovered new facets of these minute worlds within us. In a major project, more than 10,000 people from around the world mailed in their poop samples (yes, that’s right) to scientists in the US. They analysed these specimens to better understand how organisms inside us – our microbiomes – interact with diet, lifestyle and disease. Also, over the past 20 years, experts have been able to ‘fingerprint’ the gut’s cast of microbes through sequencing DNA, says physician-scientist Dr Ami Bhatt, who researches the interplay between these microorganisms and our health.
You’ve had a microbiome since the day you were born and it’s been evolving and growing within you. On your ride through the birth canal, your gut filled with microorganisms passed along by your mum. Then skin-to-skin contact, first foods, infections (and antibiotics) and all those germy toys changed your microbiome. Each new interaction, from childhood on, brings in guest stars, removes old standbys and casts long-term recurring roles – your gut’s world is constantly in flux.
Animal and human research has found the gut microbiome can also be influenced by environmental factors, such as chronic stress, artificial sweeteners, pesticides and ultra-fine particles in polluted air. You can also pick up new gut bacteria from your pet or a bad meal, Dr Bhatt notes. Ultimately, the microbial worlds that inhabit your body are wholly unique to you. Within it, helpful gut microorganisms have processes for breaking down the foods you eat and turning them into ingredients your body uses. They develop your immune system, block pathogens, synthesise vitamins and more.
Sometimes unhelpful critters stage a takeover of the gut. This overpopulation is called gut dysbiosis, an imbalance that seems to influence the brain’s everyday work. For example, gut dysbiosis is associated with depressivelike behaviours. In an animal study, transferring a mood-disordered animal’s gut bacteria into a healthy animal led to depressive symptoms for the formerly well animal, says neurologist and sleep specialist Dr Smita Patel. Other research is investigating the links between the gut microbiome and ADHD, autism spectrum disorders, anxiety and stress.
Bad gut microbes may create irritants to the immune system that travel through the bloodstream and influence the brain’s immune cells. For instance, the guts of many Alzheimer’s disease patients show a lack of diversity compared with those of similar adults and are often overpopulated with a specific microbe. This microbe may impair the body’s ability to clear a plaque built upon the brain’s structures that is related to
Alzheimer’s symptoms.
Sex-based differences come into play as well, says Dr Cox. The gut microbiota can regulate levels of hormones, including oestrogen. When gut dysbiosis sets in, oestrogen levels can change, possibly influencing cognitive decline.
Fascinating research is now being done by the Alzheimer Gut Microbiome Project in collaboration with Alzheimer’s Disease Research Centres in the US and three major diet and lifestyle modification clinical trials. At-home faecal and blood collection kits from more than 3000 racially diverse participants are being analysed to help researchers understand gut microbiome changes across the stages of Alzheimer’s disease. The project is also exploring how lifestyle and diet impacts Alzheimer’s disease–related cognitive outcomes. The findings will provide new evidence on the gut-brain axis of communication.
If researchers can home in on the precise factors that make these connections work, they may be able to slow or prevent the Alzheimer’s processes that begin in people in their 50s or even earlier. The gut houses a world of information, and we’re
learning from it every day.