We Fell For The Oldest Lie On The Internet

We Fell For The Oldest Lie On The Internet

The Surprising Truth About the Length of Your Blood Vessels

“Your blood vessels taken together add up to 100,000 kilometers, enough to wrap them around the planet twice.” This fun fact has been repeated countless times across the internet, in books, and in educational materials. But is it actually true?

In this post, we’ll take you on the year-long journey our team at Kurzgesagt went on to uncover the real origins and accuracy of this seemingly impressive statistic. What we found was a tale of outdated science, speculation, and the persistence of misinformation – a cautionary story about the challenges of verifying even the most widely circulated “facts.”

The Search for the Original Source

It all started innocently enough. Like many content creators, we at Kurzgesagt are always on the lookout for interesting and eye-catching facts to include in our videos and other materials. The “100,000 km of blood vessels” claim seemed perfect – a small, digestible piece of information that packs a big wow factor.

We had used this fact multiple times without ever really questioning where it came from. After all, a quick Google search turned up the same number repeated across countless websites, books, and academic sources. It seemed to be a well-established scientific truth.

But one day, someone asked the fateful question: where does this number actually come from? That’s when the research rabbit hole opened up.

Searching for the Source

Our first step was to try to trace the origin of this oft-repeated statistic. Surely there had to be a clear, authoritative source that we could point to, right?

Wrong. As we dug deeper, we quickly realized that not a single one of the many sources citing the “100,000 km” figure actually provided the original reference. Most didn’t cite any source at all, while others simply linked to other websites also quoting the same number.

This was our first red flag. For such a specific and widely circulated “fact,” the lack of a clear original source was highly suspicious.

Making matters worse, we found that the number was being used inconsistently across different sources. Some claimed it represented the total length of capillaries, while others said it was just the combined length of veins and arteries. There was no consensus.

Searching the Scientific Literature

Determined to get to the bottom of this, we decided to take our search to the scientific literature. Surely the original research paper or textbook that first proposed this figure must be out there somewhere.

We started with PubMed, a search engine for biomedical research papers. But our queries turned up nothing – not a single scientific publication that cited the “100,000 km” statistic.

Expanding our search, we did eventually find a handful of biology textbooks and academic papers that referenced the number. But even in these sources, there was no clear citation of the original research.

The authors we contacted told us the same thing: the “100,000 km” figure had been circulating for decades, but they didn’t know where it originated.

Tracing It Back to the 1990s

Frustrated but undeterred, we decided to narrow our search to the more recent past, focusing on the 1990s and early 2000s. Surely we’d be able to find the source if we went back a few decades, right?

And that’s when we struck gold – or at least, we thought we had. We found two books that referenced the “100,000 km” statistic:

1. “Vital Circuits” by Steven Vogel, a biomechanics professor at Duke University
2. “Looking at the Body” by David Suzuki, a renowned Canadian scientist and science communicator

These were promising leads. Vogel’s book in particular seemed to be the closest we’d come to the original source, with a direct statement about the combined length of blood vessels.

Tracking Down the Original Source

With these new leads in hand, we set out to track down the original source of the “100,000 km” claim once and for all. This is where our research journey took an unexpected turn.

Reaching Out to David Suzuki

We started by reaching out to David Suzuki, the author of “Looking at the Body.” As an esteemed scientist with decades of experience, he seemed like the perfect person to potentially shed light on the origins of this persistent factoid.

Unfortunately, Suzuki didn’t have any specific recollection of where he had obtained the “100,000 km” figure. In a letter from his public information coordinator, we were told that since the book was written over 30 years ago, Suzuki no longer had access to the files that could reveal the original source.

Digging into Steven Vogel’s Work

With Suzuki’s dead end, we turned our attention to Steven Vogel’s “Vital Circuits.” In his book, Vogel had referenced the “100,000 km” statistic, but again, without citing a specific source.

Vogel’s book did include a lengthy list of references, so we figured the original source might be buried in there somewhere. But wading through all 93 citations would have been a monumental task.

Just as we were about to give up, we decided to check the references in reverse order. And that’s when we got incredibly lucky.

The very first reference in Vogel’s list pointed us to a 1959 Scientific American article titled “The Microcirculation of the Blood.” This article, in turn, cited the original source of the “100,000 km” claim: a 1922 book by Nobel Prize-winning physiologist August Krogh, called “The Anatomy and Physiology of Capillaries.”

The Surprising Origins of the “100,000 km” Claim

After over a year of research, we had finally tracked down the original source of the “100,000 km” blood vessel statistic. And what we found was both fascinating and a bit disappointing.

August Krogh’s Estimate

In his 1922 book, Krogh – a renowned expert in the field of capillary physiology – provided the following estimate:

“Supposing a man’s muscles to weigh 50 kg and his capillaries to number 2000 per sq. mm., the total length of all these tubes put together must be something like 100,000 kilometers or 2 ½ times round the globe and their total surface 6300 sq. meters.”

So Krogh was indeed the original source of this oft-repeated factoid. But as we dug deeper, it became clear that his estimate was based on some rather shaky assumptions.

Krogh’s Flawed Assumptions

Krogh’s calculation relied on a few key assumptions:

• He used a hypothetical “ideal” human male with 50 kg of pure muscle mass, weighing 143 kg total.
• He estimated the capillary density in human muscle to be around 2,000 per square millimeter.
• He then extrapolated these figures to arrive at the 100,000 km total length.

The problem is that we now know Krogh’s assumptions were quite off the mark. Modern research has shown that the actual capillary density in human muscle is much lower, around 300-400 per square millimeter. And the average human has far less than 50 kg of pure muscle mass.

So while Krogh’s estimate was an impressive feat of scientific speculation for the time, it was ultimately an inaccurate representation of the true length of the human circulatory system.

The Latest Scientific Estimates

As our research progressed, we discovered that more recent scientific studies have provided much more accurate estimates of the total length of the human blood vessel network.

According to the latest research, the total length of all the capillaries in the human body is somewhere between 9,000 and 19,000 kilometers. That’s a far cry from the oft-cited 100,000 km figure.

This new, more accurate estimate comes from a 2020 paper published in the journal Microcirculation. The researchers used advanced imaging techniques to directly measure capillary length in human muscle samples, rather than relying on extrapolations and assumptions like Krogh did nearly a century ago.

More: The Most Insane Weapon You Never Heard About

The Persistence of Misinformation

So how did this inaccurate “100,000 km” statistic become so widely circulated and accepted as fact? Our research uncovered a few key reasons:

1. Lack of Fact-Checking: As we discovered, it’s incredibly time-consuming and difficult to trace the origins of even a seemingly simple factoid. Most scientists, educators, and content creators simply don’t have the resources to thoroughly vet every piece of information they come across.
2. The Allure of a “Beautiful” Fact: There’s no denying that the “100,000 km” figure has a certain aesthetic appeal. It’s a nice, round number that’s easy to remember and conveys a sense of scale. Facts that are visually or emotionally compelling tend to stick in people’s minds, even if they’re not entirely accurate.
3. The Snowball Effect of Misinformation: Once a piece of information starts circulating, it can take on a life of its own. Each time the “100,000 km” statistic was repeated, it gained more credibility and became harder to dislodge, even as newer, more accurate research emerged.

Lessons Learned

Our year-long quest to uncover the truth behind the “100,000 km” blood vessel claim taught us some valuable lessons about the challenges of verifying information in the digital age:

1. Question Everything, Even “Common Knowledge”

Just because a fact is widely repeated doesn’t mean it’s accurate. As our research showed, even seemingly well-established scientific “truths” can turn out to be based on flawed assumptions or outdated information. It’s important to always approach information with a critical eye and be willing to dig deeper.

2. Beware the Allure of the “Beautiful” Fact

Visually or emotionally compelling facts have a way of sticking in our minds and becoming accepted as true, even if they lack a solid evidentiary foundation. As content creators, we need to be vigilant about separating the truly factual from the merely “beautiful.”

3. Invest Time in Thorough Research

Tracing the origins of a piece of information can be a painstaking and time-consuming process. But as our experience shows, it’s often necessary to ensure the accuracy and reliability of the content we produce. Shortcuts and assumptions can lead us astray.

4. Acknowledge and Correct Mistakes

Even the most diligent researchers can sometimes get things wrong. The key is to be transparent about it, acknowledge errors, and work to correct misinformation when it’s discovered. As Kurzgesagt, we’re committed to providing the most accurate and up-to-date information possible, even if that means revisiting and revising our past work.

Conclusion: Pursuing the Truth, No Matter What

Our journey to uncover the truth behind the “100,000 km” blood vessel claim was a long and winding one. But in the end, we’re glad we persisted. By tracing the origins of this persistent factoid, we not only gained a deeper understanding of the challenges of verifying information, but we also uncovered a fascinating story about the evolution of scientific knowledge.

As content creators, our mission is to provide our audience with reliable, well-researched information. That means being willing to go the extra mile, to question assumptions, and to follow the evidence wherever it leads – even if it means admitting that something we once believed to be true was, in fact, an “oldest lie on the internet.”

We hope that by sharing our experience, we can inspire others to approach information with the same level of rigor and skepticism. After all, the pursuit of truth is what drives scientific progress and the advancement of human knowledge. And that’s a journey we’re proud to be a part of.