Hey guys! So I was thinking about making a video about the most common causes of death
in Japan, but honestly it was so similar to most other developed countries that I didn't
really see a point.
WITH ONE EXCEPTION that you may have heard of, and no it's not suicide--
It's stomach cancer.
Japan has one of the highest rates of stomach cancer in the world,
surpassed only by a few other Asian countries like South Korea and Mongolia. But why?
Well fortunately for you I did all the research so all you have to do is watch this video.
Stomach cancer was once the most common and deadliest cancer in the world, but rates over
the past 50 years have dropped dramatically in developed countries—upwards of 80%.
Today it's the 4th most common cancer and causes the second most deaths.
But Rachel almost I never hear about stomach cancer—is it really that common?
Well, not in most developed countries anymore.
The exception is in East Asia.
In fact, it's so common in Japan that a routine part of many physicals
once you reach a certain age is Esophagogastroduodenoscopy,
aka EGD, and all that is is a little camera attached to a wire that they stick down your
throat into your stomach.
It might sound strange to us that a procedure like that could be
so routine, but it has actually played a huge role in the early detection of stomach cancer,
and thanks to that survival rates in Japan are a lot higher than they are in Western
countries where that procedure still isn't very standard.
But even with that, the rate of stomach cancer in Japan
is a lot higher than most other countries in the world.
And to understand why you have to know what causes stomach cancer.
And for that explanation I'm going to give you a little bit of a history lesson.
In 1982, two scientists named Barry Marshall and Robin Warren
studying patients with gastric ulcers, or stomach ulcers, noticed
the presence of this bacteria, called Helicobacter pylori.
They believed that this bacteria was living inside the
inhospitable, acidic environments of our stomach.
They're shaped like a little corkscrew, and that shape allows them to dig their way through the mucus lining of our
stomach where they can escape attack by our immune system.
There they can attach themselves to our stomach's epithelial
cells, which are a sheet of cells that line the inside of our stomach.
And so Barry Marshall and Robin Warren developed this CRAZY idea, that this bacteria,
helicobacter pylori, was the cause of stomach ulcers.
So in other words, stomach ulcers were caused by a bacterial infection,
which is something that can be cured with just antibiotics.
Now of course the long standing thought of the time
was that stomach ulcers were caused by stress.
Even today a lot of people still believe that stomach ulcers are caused by stress.
And furthermore, they had no way of testing this on humans because you know ~ethics~
and they couldn't really test it on animals either because helicobacter pylori is so specifically
adapted to living inside humans.
And so Barry Marshall did what any normal person in pursuit
of the scientific truth would do and cultured some helicobacter pylori and DRANK IT HIMSELF.
Needless to say he got a little bit sick.
But thanks to their dedication they got people
used to the idea that chronic conditions could be caused by bacteria and in 2005 they both
won Nobel Peace prizes for their work in discovering helicobacter pylori and its role in causing
gastritis and stomach ulcers.
And as it turns out, helicobacter pylori doesn't just cause gastritis and ulcers—it also
causes stomach cancer.
It is in fact the primary cause of all forms of stomach cancer.
In 1994 the International Agency for Research on
Cancer classified helicobacter pylori as a carcinogen,
or an agent that causes cancer.
To date it is the only bacteria in the world that has been established to cause cancer.
And it is a surprisingly common bacteria.
Approximately half of the world's population
carries helicobacter pylori, although only 1-2% will ever develop stomach cancer.
It's passed through the fecal to oral route, or more commonly in developed countries, the
oral to oral route, and is primarily picked up in childhood.
It has actually evolved with humans, and has been a part of
our digestive flora since before humans originally migrated out of Africa.
But even though it's found worldwide, as you'll remember at the beginning
of the video I said that cancer rates are highest in East Asia.
And in fact Africa has higher infection rates of helicobacter
pylori, but they have lower rates of stomach cancer.
But why?
Well first of all, there are two types of
helicobacter pylori—CagA positive and CagA negative.
CagA stands for cytotoxin-associated gene A.
Cytotoxicity means something is toxic to cells,
like venom from a snake or a spider, for example.
So CagA positive helicobacter pylori bacteria are toxic to cells.
Helicobacter pylori that are CagA positive have a needle-like
structure in them that they use to stick into their host cell and inject CagA protein.
Now, I'm going to get a little bit complicated for just a moment, so bear with me.
Epithelial cells, remember, the cells lining the inside of your stomach, stick together and form a
barrier so that things can't pass through them.
This place where they stick together is called a tight junction.
Now, when they're injected with CagA protein, this tight junction
breaks apart and the cells begin shifting and moving and changing shape by elongating,
a process which is called the "hummingbird phenotype."
Now that's just a name with big words in it, so don't be too scared!
This process is reminiscent of a process called
Epithelial-Mesenchymal transition, or EMT.
When this process is supposed to happen, that's a good thing.
But when it's not supposed to happen, it can be a factor in the metastasization of cancer.
When cancer metastasizes, that means it's spreading to another part of the body.
So you have your barrier of epithelial cells that are breaking apart and moving around,
which means that they can now pass through the hole in the barrier that they created
and enter your body's bloodstream, which is on the other side of your epithelial cells.
Your bloodstream is like a highway for cells, so when bad things enter it that means they
can spread throughout your entire body and be deposited somewhere else.
Now, if that epithelial cell that was injected with
CagA becomes cancerous, then that means there's a
chance that that cell can enter your bloodstream
and form a new tumor somewhere else in your body.
That is one way that cancer can metastasize.
So, we know all of this can happen with epithelial cells that are injected with CagA, and while
we have theories, we don't yet know exactly what causes those cells to turn cancerous
in the first place.
But, back to a less complicated subject!
So that CagA protein is one thing
that contributes to an increased rate of stomach cancer in people who have helicobacter pylori.
And, unfortunately for East Asia, most helicobacter pylori there is CagA positive.
But there's one other thing that makes the rate of stomach cancer in Japan so high, and
that is the fact that helicobacter pylori is divided into different strains depending
on where you are in the world.
There are two primary CagA positive strains—the Western
CagA positive strain and the East Asian CagA strain.
And unfortunately for East Asia, the East Asian CagA strain is much
more virulent and causes cancer a lot more often than the Western one.
And so that's how Africa can have 80-90% infection rates with helicobacter
pylori but still have less cancer than East Asia, which only has approximately 60% infection
rates.
But there's one other interesting thing that you might want to know.
According to one study, the risk of getting stomach
cancer in the Philippines is 6 per 100,000 people.
That's compared to approximately 6 in America and Canada, and 46 in Japan.
Given the historical migration of its people you might expect the Philippines to have the East Asian strain
of helicobacter pylori, but it doesn't.
Despite having primarily CagA positive bacteria, the
Philippines was found to have the Western strain as opposed to the East Asian strain
and thus enjoys a relatively low rate of stomach cancer.
The study suggests that the reason they might have primarily the Western
CagA strain is due to the strong influence of Western colonization.
Now, I would like to take a moment to separate this part of the video.
Everything I have said until now has been me reporting on science.
What I'm going to say from now is non-scientist
me making stupid suggestions so please don't confuse the two.
Considering the fact that helicobacter pylori is primarily transmitted through the oral
to oral route, and considering the fact that the Philippines may have originally had an
East Asian strain of helicobacter pylori that was replaced by a Western strain, then I'm
just wondering if maybe Japanese people could maybe reduce their risk of stomach cancer
if they went out and made out with a couple foreigners?
I dunno, sounds like it couldn't hurt to me.
I think there's probably a bunch of foreign volunteers subscribed to our channel,
so I'm just saying maybe you should make some friends... for science.
I mean, am I the only one who reached this conclusion?
I think it would be interesting if we could see the rates
of stomach cancer for Japanese people who are married to foreigners versus Japanese
married to other Japanese people.
So anyway, non-scientist me is just gonna go ahead and make this claim:
Kiss some Japanese people, save some lives.