00:00:01
Fever feels bad. So we take medication
to suppress it – but is this a good idea?
00:00:08
It turns out fever is one of the oldest defenses
against disease. What exactly is it, how does
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it make your immune defense stronger
and should you take a pill to combat it?
00:00:22
The Heat of Life
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On earth life is able to thrive between
the extremes of -10°C in deep cool
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pools and 120°C in thermal vents. Step outside
this range and die. Every animal or microbe
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has a temperature range that is ideal and one
that is stressful but survivable for a while.
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Your ideal temperature is where your cells
work best, where their internal machinery
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is the most efficient and the animal as
a whole the best adapted to its niche.
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Humans are warm blooded animals and our bodies
expend a lot of energy to keep us around 37°C
00:00:58
or 98.6 °F. Which seems wasteful, but this
may actually be a defensive adaptation – our
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temperature makes us almost entirely immune
to one of the worst killers and parasites:
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Fungi. Most colder animals and their insides
are infected by them - but you are just too hot!
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Which brings us to fever. For any microbe that
wants to infect you, your body is a world they
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want to conquer. Fever is defensive climate change
pushing an invader outside its ideal temperature
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range and making the world horrible. It evolved
at least 600 million years ago and is widespread:
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most animals increase their core
temperature when they are sick.
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Fish swim into warmer waters,
lizards bathe in the sun. Bees
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heat up the air inside their hive.
But you, warm blooded mammal,
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you have way more drastic options. Let's
make you sick and see what happens.
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When Your Blood Turns Into Lava
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You're invaded by bacteria and viruses at
the same time. The invasion is powerful and
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you need to slow it down as fast as possible.
Fever is part of your first line of defense,
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triggered by a diverse group
of chemicals called “pyrogens”,
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“The creators of heat”. They float away from
the battlefield and pass right into your brain,
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where specialized receptors pick them up
and crank up your internal thermostat.
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First you begin to shiver. Your skeletal muscles
contract really quickly, which generates a lot of
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heat in your core. At the same time usually the
blood vessels near your surfaces contract and
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prevent heat from escaping through your skin.
Your skin cools down while your insides burn.
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Fever is a systemic, body wide response and
is a serious energy investment for your body.
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You burn about 10% more calories to stay
alive for every degree centigrade your
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body temperature rises. Fever is also
a strong order to lay down and rest,
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to save energy and give your
immune system time to fight.
00:03:02
Back to the battlefield: When the bacteria entered
your body they tried to be stealthy. But now they
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have switched into high production mode. Their
goal is to multiply as fast as possible, which
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means they need a lot of resources and are highly
stressed. Imagine running a marathon while eating
00:03:18
a succulent chinese meal and giving birth. The
last thing bacteria need right now is more stress.
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So your immune system tries to stress them out
as much as possible by ordering inflammation,
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which floods the battlefield with fluids,
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attack proteins and soldiers. Pretty
stressful! Fever is even more stress!
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For the bacteria a moment ago the
temperature range was pleasant,
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now the world burns! Heat can cause their
organs to break and membranes to rupture,
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damage their DNA and diminish protein production.
They are seriously suffering from the heat.
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Why doesn't this affect your cells? It does!
All of this is stressful for your cells too!
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Virtually every system and organ of your
body works worse during fever – except one:
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Your immune system. Neutrophils are recruited
faster, Macrophages and Dendritic Cells are
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better at devouring enemies, Killer Cells
kill better and so on. And fever animates
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your immune cells to gobble up the critical
resources your enemies need, like iron,
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glucose and glutamine, turning the
battlefield into a food desert.
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The viruses that infected millions of cells are
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doing even worse because they are also
very sensitive to heat. For example,
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The rhinovirus that causes the common
cold can only infect your respiratory
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tract because it is significantly colder than
the rest of your body, even without fever.
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The heat is also really bad for the millions
of cells that are infected by viruses
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at this point. They are working super hard
producing viruses, which is pretty stressful.
00:04:54
As the heat becomes too much to bear, the
super stressed cells panic. As their internal
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machinery is breaking and failing they quickly
produce billions of heat shock proteins,
00:05:04
or HSPs, that start repairs, keeping them alive.
00:05:09
But this is a trap.
00:05:11
Even your healthy cells produce HSPs to deal with
the heat – but if a cell makes too many of them,
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this means it is more stressed than it
should be. And if it is too stressed,
00:05:21
something is wrong and it should be killed. So
your Natural Killer Cells and Killer T Cells are
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activated and attracted by HSPs and start
killing infected cells and all the viruses
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inside them. By trying to protect themselves,
infected cells are calling out to be destroyed.
00:05:40
But if fever is such an effective weapon,
00:05:43
why don’t your enemies adapt to it? How is it
still viable, in so many different animals,
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after hundreds of millions of years? A wild reason
is that fever actually might outsmart evolution.
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If your enemies survive fever long
enough, natural selection changes
00:06:00
them. The individuals that are better suited to
deal with heat reproduce more. After a few days,
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they have adapted. But this becomes
a handicap – because the next step is
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to infect new victims in new bodies, and
now healthy humans are too cold for them!
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Not impossible to infect, just harder. And
the heat resistant microbes now compete
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with their cousins that like it colder
and have an advantage infecting healthy
00:06:27
hosts. This creates an evolutionary
dilemma without a perfect solution.
00:06:33
To circumvent this, serious pathogens like
measles use hit and run tactics. The measles virus
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replicates ultra fast and is the most infectious
right before your fever hits with full force.
00:06:42
It's brutally beaten back once your full immune
response shows up. But by then the damage is done.
00:06:49
Fever is an effective part of
the puzzle of your immune system,
00:06:52
helping to attack and stress your
enemies from as many angles as
00:06:55
possible. But if fever is so great,
why do we stop it when we are sick?
00:07:01
Should you Fight Fever with Medications
00:07:05
We think it is normal to have magic
pills, but relatively harmless,
00:07:08
over the counter pain medication like Aspirin or
Ibuprofen only became cheap and widely available
00:07:14
in the last century or so. Going to a pharmacy to
get something for your headache is extremely new
00:07:19
in human history. Pain feels bad, so we've
gotten used to stopping it when we feel it.
00:07:25
If you are sick, you're supposed to feel a reasonable
amount of pain so you lie down and save energy.
00:07:30
This is not a bug but a feature of your immune
system. But pain and fever are closely connected
00:07:35
and over the counter pain medication like
Ibuprofen and Paracetamol also work against fever.
00:07:41
Especially in children fever is often suppressed
by worried parents or doctors – sometimes because
00:07:47
they think fever itself is the disease or they
are worried that it can do long term harm.
00:07:53
In general it's fair to say that for temperatures
below 40°C or 104 °F, fever is not dangerous
00:08:00
and doesn’t need to be treated.
Of course there are also patients
00:08:03
that should not have fever – like pregnant
women, seniors and seriously weakened
00:08:07
patients. For them the extra stress may be
dangerous. Fever over 40°C is dangerous to
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anybody because it's most likely caused
by your internal heat monitor failing.
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Things get more complicated
in serious disease territory.
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We also have evidence that for
some diseases like influenza
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or chickenpox antifever drugs
do not help you to heal faster.
00:08:30
But we are also running
into ethics problems here
00:08:32
that make clinical trials difficult. In one
study doctors gave strong anti fever treatment to
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critical care patients – but had to stop
after mortality shot up. Overall we have
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strong indications that more people may survive
serious infectious diseases better with a fever.
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And there is very little clinical
evidence that stopping fever leads
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to better health outcomes. But
there are important exceptions,
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like neurological injuries and stroke.
We definitely need a lot more research.
00:09:00
So should you fight fever? Well, speak to
your doctor and don’t listen to internet
00:09:06
videos. But this decision is really about
payoffs. If a fever is not dangerously
00:09:11
high and you can bear it, you are supporting
your defenses and may even get healthy a bit
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faster. But if you feel really bad
and are healthy in general,
00:09:21
taking a pill against pain and fever
will make you feel better quicker,
00:09:25
at the cost of a slightly
less effective immune defense.
00:09:28
However you decide, the next time
you are burning up and feeling bad,
00:09:32
you can rest easy in the knowledge that your
enemies are having a much worse time than you.
00:09:40
It’s thanks to doctors and researchers
that we have these insights – we’re just
00:09:44
doing our part by bringing them to
you. If you are also aiming to make
00:09:48
a positive difference in the
world, where should you start?
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