The repeated reminder to keep getting sun (if your able) (like 1hour a day if possible (more if darker skin tone)) and takeing vitamin D suppliments.
If you cannot, or have darker skin (so it takes much longer to make vitamin D), you should be on a suppliment for your own safety.
John Campbell:
https://www.youtube.com/watch?v=qyMFsLFAE5o
98.9% of covid19 patients defined as vitamin D deficient (below 20ng/ml) died.
While only 4,1% of patients with high enough levels died.
Thats from Indonesia, where they looked at ~800 patients history at a hospital that had Covid19.
(ei. you got a bad case of covid and were hospitalised)
Basically you get hit hard with covid19, and you have a deficiency in Vitamin D, chances of you dieing are so much higher its unreal.
In the UK they did studies about Vitamin D levels (Annualised mean levels):
So the yearly avg was:
White ~45,8 nmol/L (john campbell says this is too low as well) (he basically sees the entire UK as being deficient in general)
Asian ~20,5 nmol/L
Black ~27,7 nmol/L
So your thinking, why would asians have lower levels than blacks? Well bacause the black people in the UK arnt afraid of sun bathing abit or being outsides in the sun. Asians in general have this thing about light fair skin, not wanting to tan, and also because "asians" here means muslims (in the uk), and the women are typically always covered up (ei. if only your face can get sun light, and not arms/legs ect, you make less Vitamin D).
This is (a large part of) why asian & black people make up a disproportional amount of infections for covid19,
and have higher deaths than whites in the UK.