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Visualizing the Relationship Between Cancer and Lifespan

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Visualizing the Relationship Between Cancer and Lifespan

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A Newfound Link Between Cancer and Aging?

A new study in 2022 reveals a thought-provoking relationship between how long animals live and how quickly their genetic codes mutate.

Cancer is a product of time and mutations, and so researchers investigated its onset and impact within 16 unique mammals. A new perspective on DNA mutation broadens our understanding of aging and cancer development—and how we might be able to control it.

Mutations, Aging, and Cancer: A Primer

Cancer is the uncontrolled growth of cells. It is not a pathogen that infects the body, but a normal body process gone wrong.

Cells divide and multiply in our bodies all the time. Sometimes, during DNA replication, tiny mistakes (called mutations) appear randomly within the genetic code. Our bodies have mechanisms to correct these errors, and for much of our youth we remain strong and healthy as a result of these corrective measures.

However, these protections weaken as we age. Developing cancer becomes more likely as mutations slip past our defenses and continue to multiply. The longer we live, the more mutations we carry, and the likelihood of them manifesting into cancer increases.

A Biological Conundrum

Since mutations can occur randomly, biologists expect larger lifeforms (those with more cells) to have greater chances of developing cancer than smaller lifeforms.

Strangely, no association exists.

It is one of biology’s biggest mysteries as to why massive creatures like whales or elephants rarely seem to experience cancer. This is called Peto’s Paradox. Even stranger: some smaller creatures, like the naked mole rat, are completely resistant to cancer.

This phenomenon motivates researchers to look into the genetics of naked mole rats and whales. And while we’ve discovered that special genetic bonuses (like extra tumor-suppressing genes) benefit these creatures, a pattern for cancer rates across all other species is still poorly understood.

Cancer May Be Closely Associated with Lifespan

Researchers at the Wellcome Sanger Institute report the first study to look at how mutation rates compare with animal lifespans.

Mutation rates are simply the speed at which species beget mutations. Mammals with shorter lifespans have average mutation rates that are very fast. A mouse undergoes nearly 800 mutations in each of its four short years on Earth. Mammals with longer lifespans have average mutation rates that are much slower. In humans (average lifespan of roughly 84 years), it comes to fewer than 50 mutations per year.

The study also compares the number of mutations at time of death with other traits, like body mass and lifespan. For example, a giraffe has roughly 40,000 times more cells than a mouse. Or a human lives 90 times longer than a mouse. What surprised researchers was that the number of mutations at time of death differed only by a factor of three.

Such small differentiation suggests there may be a total number of mutations a species can collect before it dies. Since the mammals reached this number at different speeds, finding ways to control the rate of mutations may help stall cancer development, set back aging, and prolong life.

The Future of Cancer Research

The findings in this study ignite new questions for understanding cancer.

Confirming that mutation rate and lifespan are strongly correlated needs comparison to lifeforms beyond mammals, like fishes, birds, and even plants.

It will also be necessary to understand what factors control mutation rates. The answer to this likely lies within the complexities of DNA. Geneticists and oncologists are continuing to investigate genetic curiosities like tumor-suppressing genes and how they might impact mutation rates.

Aging is likely to be a confluence of many issues, like epigenetic changes or telomere shortening, but if mutations are involved then there may be hopes of slowing genetic damage—or even reversing it.

While just a first step, linking mutation rates to lifespan is a reframing of our understanding of cancer development, and it may open doors to new strategies and therapies for treating cancer or taming the number of health-related concerns that come with aging.

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Healthcare

Visualized: What Lives in Your Gut Microbiome?

The human gut microbiome contains a world of microbes. We look at the the bacteria that deeply affect our health and well-being.

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Visualized: What Lives in Your Gut Microbiome

Inside all of us lies a complex ecosystem of microbes. It includes bacteria, fungi, and even viruses that live in virtually every part of our bodies.

Researchers are continuing to discover how deeply connected our overall gastrointestinal health—gut health—is to these microbes.

Because bacteria outnumber all other microbes, we take a look at which ones live inside of us and what they do.

The Bacteria of the Gut Microbiome

The gut microbiome is composed of six main types of microbes. Each of these types of microbes has a unique function and role within the human body:

  • Firmicutes: Firmicutes break down complex carbohydrates and produce short-chain fatty acids for energy. They help maintain the functioning of the gut barrier, which obstructs bacteria, harmful microorganisms, and toxins from entering the bloodstream through the intestinal tracks. Firmicutes are also linked to obesity and metabolic disorders when imbalanced.
  • Actinomycetota: Actinomycetota break down complex carbs and produce vitamins B12 and K2, which are crucial for calcium absorption and energy generation in the body. They also protect the gut from harmful pathogens.
  • Pseudomonadota: Pseudomonadota lowers the gut’s redox potential, a measure of the balance between oxidants and antioxidants in the gastrointestinal tract. This is important for breaking down, storing, and using energy. They do this by producing short-chain fatty acids and breaking down complex molecules, promoting the growth of other beneficial gut microbes.
  • Fusobacteriota: Fusobacteriota can activate inflammatory responses to fight pathogens. But when imbalanced, they can contribute to inflammation and disease, such as periodontal disease.
  • Bacteroides: Bacteroides break down complex carbohydrates, regulate the immune system, and produce vitamins and metabolites important for overall health in the human gut microbiome.
  • Other: The “other” category includes a diverse range of microbes that contribute to various functions within the gut. These include various types of bacteria including TM7 (oral bacteria), cyanobacteria, acidobacteria, and verrucomicrobiota.

Dynamic Composition of the Microbiome

Interestingly, the proportions of these six microbe populations vary throughout the gastrointestinal tract.

Section of Gut MicrobiomeExponential Microbial Population (CFU/ml)Dominant Microbe
Mouth10⁵Firmicutes
Esophagus10⁷Firmicutes
Stomach10³Actinomycetota
Duodenum (Small Intestine)10³Firmicutes
Jejunum (Small Intestine)10⁵Firmicutes
Ileum (Small Intestine)10⁸Firmicutes
Large Intestine10¹⁰-10¹²Bacteroides

The presence, absence, and dominance of each of these microbes is based on their functionality. For example, in the mouth and esophagus, the microbial populations are relatively low. But the dominant microbe found here, Firmicutes, helps begin the process of breaking down sugars and carbohydrates from ingested food.

Meanwhile, the stomach is a harsh environment, with low pH levels that limit microbial growth. A small population of microbes is still present here.

The microbial population becomes more diverse in the small intestine. Here, Firmicutes and Actinomycetota are the dominant species, but Bacteroides and other microbes begin to make up a more substantial portion of the population.

The microbial population further diversifies in the large intestine, with Bacteroides and other microbes making up the majority of the population.

These proportions of bacteria in the gut microbiome represent the typical ratios for the average human body. But they can be influenced by factors including medical history, diet, age, and even geographical location.

The Gut-Brain Axis

The six microbe populations have effects way outside the gastrointestinal tract too.

The Gut-Brain Axis is a two-way link between the gut and the brain. This connection involves physical pathways and various forms of communication, including hormones, metabolism, and immunity.

Through these connections, the gut sends the brain signals when troubled. A distressed stomach or intestine is linked to anxiety, stress, depression, and other mental health issues. Irritable bowel syndrome (IBS) is another example of a disease influenced by the gut microbiome.

At the same time, the brain also signals the gut when distressed. Scientists believe that emotions like anger, anxiety, sadness, and happiness trigger gut issues.

Towards a Healthy Gut

The gut is known as our body’s “second brain” and more and more people are now paying close attention to their gut health.

Over the last two decades, we’ve gained a better understanding of how the microbiome affects human health. One example of this is the gut-brain axis. Changes in the microbiome have also been connected to various diseases.

Understanding this microbiome has opened up new opportunities in medicine and healthcare, as the knowledge of the role of every microbe could also uncover new treatments for illnesses linked to it.

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