By Andrea Mcbeth
Scurvy, the disease of pirates and sailors, was particularly prevalent during long sea voyages in the 15th to 18th centuries. It is a disease that results from a deficiency in Vitamin C, a nutrient required for the synthesis of collagen in humans. These sea journeys often lasted for months without any fresh produce, leading to a severe lack of Vitamin C in sailors' diets. The primary diet during these voyages consisted of preserved foods like hardtack (a type of dry biscuit) and salted meat, which were devoid of this essential vitamin. The story of its discovery and the subsequent realization of its cause provides an excellent example of how critical a single nutritional component can be for human health.
The symptoms of scurvy are initially nonspecific and include fatigue, malaise, and depression. As the disease progresses, more telling signs like swollen, bleeding gums and reopening of previously healed wounds become apparent. This is due to the degradation of collagen, a vital protein that helps in wound healing, skin health, and maintaining the integrity of blood vessels. In its most severe form, scurvy can lead to death.
The connection between scurvy and Vitamin C deficiency was made by British naval surgeon James Lind in the mid-18th century. Through a controlled experiment on sailors suffering from scurvy, Lind found that those who consumed citrus fruits, a rich source of Vitamin C, showed significant improvement. This led to the British Navy adopting the practice of providing sailors with lemon or lime juice during long voyages, effectively curbing the scurvy epidemic. That's why British sailors came to be known as 'limeys'.
This historical episode underscores the importance of a single nutritional element in human health, which can be a useful analogy when talking about the potentially thousands of critical metabolites produced by a diverse gut microbiota. Just like sailors on a long voyage, modern lifestyles may leave us deficient in these key microbiome derived metabolites, and supplementing them might lead us to the solutions for our current day epidemics.
Our discovery and understanding of the human microbiome has been dramatically reshaped in the past few decades, bringing to light an alarming trend. The diversity of our microbiota, the vast ecosystem of microorganisms within us, is dwindling at an unprecedented rate. This shift, akin to the loss of biodiversity seen in the natural world, is increasingly linked to the rise in chronic diseases.
The modern lifestyle, particularly in urbanized societies, is a key player in this emerging health crisis. We have created a built environment that distances us from the rich array of environmental microbes that shaped our ancestral microbiome. The food and water we consume, processed and sterilized, are stripped of the microbial life that our bodies have co-evolved with over millennia. Moreover, our increasingly sedentary lifestyle further compounds this problem by reducing our exposure to the diverse microbial life present in nature and limiting the physicality we evolved to need for normal metabolic functioning.
The increased use of antibiotics, while lifesaving in many instances, also contributes to the depletion of our microbiome. Broad-spectrum antibiotics can decimate our microbial inhabitants, including the beneficial ones, leading to long-term disruptions in our microbiome.
A central aspect of our modern lifestyle that is affecting our microbiome is our diet. Pre-industrial human societies consumed a varied diet rich in fiber from a wide variety of plants. These fibers, indigestible by our bodies, serve as food for our gut microbes, allowing them to flourish and maintain a healthy diversity. However, in the industrialized world, our diets are increasingly dominated by processed foods low in fiber and high in simple sugars and fats. This shift in dietary habits deprives our gut microbes of the diverse nutrients they need to thrive, leading to a less diverse microbiome.
Urban living, a lack of microbial exposure due to overly sanitized environments, antibiotic use, and low-fiber diets have created a perfect storm for the diminishment of our microbiota. This is especially concerning considering the essential role our microbiome and its metabolism plays in our overall health, including its influence on our immune system, metabolism, and even our brain function.
In a narrative reminiscent of the scurvy tales of the past, we are experiencing an insidious form of 'microbial scurvy' brought about by a deficiency not in Vitamin C, but in the variety of compounds our microbiota derives, extracts, or produces from a fiber-rich diet. Like the sailors of old, replenishing what has been lost - in this case, our ancestral microbiome's diverse metabolism - could be a key strategy in navigating the current chronic disease epidemic. The next step is to investigate potential solutions, including dietary modifications to boost fiber intake and perhaps nutritional supplementation with key microbiome metabolites, to restore and conserve our internal ecosystem.
The mystery of what are these modern day versions of Vitamin C is becoming more intricate as we unearth further the profound interplay between our body and the trillions of microbes that share our personal biological universe. Each new discovery is akin to opening a new chapter in a book we thought we knew, only to find the story is far more complex than we could have ever imagined.
Consider the recent discovery of microbial bile acid metabolites, or MCBAs, a set of compounds that represent a clear dialogue between our gut microbiota and our human cells. For years, we've known that bile acids, produced by our liver, play a critical role in the digestion and absorption of dietary fats. But MCBAs shed a new light on the versatility of these compounds. Altered by gut microbes, these bile acids take on new roles, influencing our body's functions from the digestion of nutrients to regulating inflammation and metabolic processes. In essence, our physiology is part of a larger, interwoven metabolic framework that extends beyond our human cells.
As we delve deeper we uncover the multifaceted roles of short-chain fatty acids (SCFAs). When our gut microbes ferment dietary fibers, they create SCFAs, such as acetate, propionate, and butyrate. We have long known these molecules nourish our gut lining, but recent studies have shown they do so much more. They interact with the cells of our gut lining and can stimulate enteroendocrine cells, which in turn interact with our vagus nerve – a direct line of communication to our brain. It's a chain of whispers, starting with what we eat and ultimately influencing our brain activity, behavior, and overall health.
Further still, gut microbes produce a range of molecules derived from dietary tryptophan, an essential amino acid. Some of these tryptophan derivatives are precursors to important neurostimulatory molecules like serotonin, kynurenine, and indole, which have a major influence on our mood, cognition, and even our sleep patterns. The discovery of these pathways has illuminated our understanding that our microbes might be critical conductors in the orchestra of neurotransmitter production and regulation.
As we bring these new discoveries together we start to see our sophisticated human biology is not entirely our own. Many of our fundamental biological processes likely have their roots in our ancient microbial ancestors. The concept that our mitochondria, the powerhouses of our cells, were once free-living bacteria is a compelling testament to this idea. We've come to understand that these vital components of our cells, which generate the energy that fuels our bodies, are likely the result of an ancient endosymbiotic event - a merger of two organisms to create something new, more complex, and co-dependent.
These revelations, exposing our interconnectedness with our microbial partners, carry us back to the story of scurvy. With a renewed lens, the tale of the sailors appears to be an early, tangible example of the role our microbes play in maintaining our health. The sailors' journey showed us that some key nutritional needs, like Vitamin C, must be acquired from our diet. As we delve deeper into the microbiome, it's becoming clear that the Vitamin C example is not isolated; it could be just the tip of the iceberg.
What we have traditionally classified as 'vitamins' are compounds essential for our health that our human cells can't synthesize. We've identified a few dozen of these to date, but with our newfound understanding of our microbiota, we might need to redefine our concept of vitamins. This isn't to suggest that the nutrients we've been studying for centuries are any less significant. Rather, there may be a plethora of previously unidentified 'microbial vitamins' — compounds our microbes synthesize that are equally essential to our health.
As we continue to explore this microbiome frontier, we may find that our microbial partners supply us with a vast repertoire of these critical nutrients. So perhaps we need not only the Vitamin C in our citrus fruits, but also a thriving, diverse microbiome to keep our health in balance.
Just as the understanding of Vitamin C transformed the health of sailors centuries ago, so might our understanding of these 'microbial vitamins' revolutionize health and medicine in the near future. Like explorers on an unknown sea, we're embarking on a journey of discovery, learning how to navigate and harness the power of our inner microbial world. Our health, it appears, depends as much on these microscopic passengers as it does on our human cells. And so, the story of our health continues to unfold, expanding to include the vast, uncharted microbiome that dwells within us.
References:
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