That's an absurd analogy. Vitamin D is a vitamin that is in large part derived from significant sunlight exposure. Vitamins are essential by definition. Sunlight exposure is highly insufficient by historical standards. This is why supplementation is absolutely necessary in almost everyone who is not a full time outdoor worker.

In contrast, the air contains oxygen which is sufficient for most people with normal lung function.

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gblargg a day ago | parent [-]

If most people have a significant Vitamin D deficiency, then I agree that my comparison was absurd.

	▲	d2kx a day ago \| parent \| next [-]
		Probably heavily depends on the country/region, but here in Germany it is basically the norm to be Vitamin D deficient. Like, half of the population have a deficiency when there is some sun and basically everyone has a deficiency for months during fall/winter/spring. So I have to laugh when I read "taking vitamin D does nothing unless you’re severely deficient". Yeah like, but that's most people in many countries lmao
	▲	OutOfHere a day ago \| parent \| prev [-]
		Without supplementation, yes, most people do have a substantial deficiency. There also exists the sufficiency range which is higher, and the optimality range which is slightly higher still.