This reminds me of the fact that humans used to be able to hibernate (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1117993/) and (https://www.popularmechanics.com/science/a35033907/early-hum...)
"They chose to spend the worst part of the year trying to sleep through it inside of relatively safe caves, and to do that, they sacrificed nutrition and vitamin D from the sun."
Also it does not really matter for your vitamin D levels, if you are outside in winter in the north or in a cave. The sun is too low for the body to produce Vitamin D anyway (only the Inuit for example do not need sun, to produce Vitamin D btw. )
And that they lacked nutrition in winter can also just mean, that there simply was not much food in the winters, which is kind of expected, before humans developed storage and preservation technologies?
As far as I can tell, they need vitamin D just like any other life form and can only synthesise it from the sun, just like all other lifeforms on Earth.
They might have adapted to reduced amounts of available vitamin D though[0], because they don't have much of it available to them in the first place and because there's really no other source than producing your own from the sun, or eating things that have produced it from the sun. So they have a vitamin D deficiency, but it's less severe than for most people.
[0]https://www.erudit.org/en/journals/etudinuit/2016-v40-n2-etu...
Note that numerous of the sources listed here are fortified (that is, have additional vitamin D added), however it does occur naturally in some sources as well:
<https://www.dietaryguidelines.gov/resources/2020-2025-dietar...>
The claim I was responding to was "they [unlike other humans] don't need sun to produce vitamin D". They do, they just don't rely much on this source because it doesn't work in their environment.
We both could have communicated more clearly :-/
Agreed, and what I was trying to say was that sunlight isn't the exclusive route.
That is, either sunlight or dietary supplementation will provide the essential vitamin/hormone D (its biological function is ... interesting).
Which is to say, deprivation of either sunlight or dietary sources of themselves is not sufficient to induce vitamin D deficiency. There's also the fact that as an oil-based vitamin, can be, and is, stored for prolonged periods in body tissues. That's a sharp contrast to the water-soluable vitamin C of which excess is excreted in urine.
This was responding specifically to the prior claim "they need vitamin D just like any other life form and can only synthesise it from the sun" (emphasis added) by seszett here: <https://news.ycombinator.com/item?id=40594479> The apparent claim that sunlight is necessary for acquisition of vitamin D is incorrect.
Periodic hypersupplementation of D can be effectively processed and retained by the body. By contrast, hyperdosing of vitamin C is a waste of resources as the excess is not retained and is flushed out. I've read previously that long-term injections of vitamin D have been effectively used, see:
"Lasting Moderate Increases in Serum 25-Hydroxvitamin D Levels and Shorter-Term Changes in Plasma Calcium " <https://pubmed.ncbi.nlm.nih.gov/28492140/>
"Vitamin D Injections: Benefits, Side Effects, and Who Is a Candidate? " <https://healthnews.com/nutrition/vitamins-and-supplements/vi...>
(Neither of these is the specific item I'd had in mind, though both describe similar procedures and efficacy.)
(Overconsumption of various vitamins and minerals can be harmful in other ways as well, I'm not a doctor (not even of philology) and moreover I'm not your doctor.)
https://www.nature.com/articles/nature12788
Our last common ancestor was ~990k years ago (table 1). That's quite long ago in human development