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Comment by aidenn0 | Hacker News Reader

My sister got leukemia while part way through her doctorate. After it went into remission, she was unable to recall new information long enough to read papers and had to put her studies on hold. Eventually a doctor did a blood test that included vitamin d levels, and she was in the single digits (don't remember units but it was supposed to be at least 20). She started supplementing and graduated this spring. Just one data point, but it was pretty clear that remedying a deficiency made a marked improvement in her case.

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The interesting analogy Ross Tucker (https://sportsscientists.com/who-are-we/) uses is adding vitamins and mineral is like adding a wheel to a car. If you onyl have 3, then adding the 4th is really going to make a massive difference. If you already have enough however, it's like adding a 5th wheel, which will essentially do nothing, and could be harmful.

It works well as an explanation, as people do seem to try and reduce complex functions to simple rules, and extrapolate from specific populatiosn to create general rules (not helped by studies that are minimally generalisable)

Also look at Liebig's barrel (https://en.wikipedia.org/wiki/Liebig%27s_law_of_the_minimum#.... It was originally applied to plant growth, but it is a helpful metaphor for vitamin substitution.

Vitamin D is vital for adaptive immune system function too!

When a T-cell encounters a foreign pathogen, it extends a vitamin D receptor. A signaling device allowing it to bind to the active form of vitamin D. Only after this can T-cells perform their intended function. [1]

Which is likely why healthy levels > 40 ng/mL significantly reduce COVID mortality, there's been > 2 dozen obersvational studies and at least one randomized controlled one. [2]

1. von Essen MR, Kongsbak M, Schjerling P, Olgaard K, Odum N, Geisler C (April 2010). "Vitamin D controls T cell antigen receptor signaling and activation of human T cells". Nature Immunology. 11 (4): 344–49. https://doi.org/10.1038/ni.1851

2. Entrenas Castillo, M., Entrenas Costa, L. M., Vaquero Barrios, J. M., Alcalá Díaz, J. F., López Miranda, J., Bouillon, R., & Quesada Gomez, J. M. (2020). "Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study". The Journal of steroid biochemistry and molecular biology, 203, 105751. https://doi.org/10.1016/j.jsbmb.2020.105751

Similar story. My mind was in fragments from diseases. Vit D in low teens. Started high level vit D at start of Covid Brain function is approaching my old levels. Now I take a lot of supplements, so it’s always tricky to pin it down. But so far so goods.

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