It doesn’t seem like a huge difference to me but even a 1 degree increase of body temp can make you so tired and have fever. Why is that?
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Fever is caused by the immune system(white blood cells) releasing chemicals like interleukin 6 and TNF alpha to raise the body temperature for optimal macrophage and NK cell function- these bad boys are the ones which “eat” the bacteria/virus.
The height of fever is an interplay between how strong the host response is – depends of the immune health of host and the immunogenicity of the virus/bacteria.
Like influenza virus typically causes very strong immune response due to the similarity of the virus proteins to human proteins.
The reason you feel like shit are these
1. If you are 70kgs, raising the body temperature by 2 C is going to take 70×2 = 140 Kcal. Imagine keeping it high for 1 to 2 hours. It’s going to use up close to 400Kcal. Imaging running for 45 minutes. You will feel exhausted. And this cycle repeats 2 to 4 times per day.
2. Glycogen is used as an immediate source of energy to raise body temperature in acute infections. Using glycogen uses a lot of water. So you get dehydrated. Add to that the fact that decreasing body temperature entails sweating causing you to lose salt and water.
So loss of energy, water and salt- enough to wipe you out .
3. Even without the thermodynamics , TNF which is a chemical released to cause inflammation- makes you fatigued and lose appetite. My theory is that, in olden times, it was a protective reflex to prevent you from needing to go out and hunt.
Hope that explains it.
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