Not a fan or even their user but kudos to Google for admitting the failure. Amazon (at least AWS) customers would have probably been shown a green dashboard and told to review their code.
While there are studies on 25-OH-D metabolism impacting melatonin production, I can only find studies done with Multiple Sclerosis patients [1]. There are also studies showing that LOW levels of 25-OH-D may have negative impact on sleep [2][3][4]. While I am unable to present scentific evidence, I would like to state that for me - personally - taking vitamin D3 in the afternoon has similar effects to ingesting caffeine. I have no reason to believe that I might be suffering from Multiple Sclerosis. Without evidence you are free to ignore it as a placebo/nocebo effect. YMMV based on age, ethnicity, sunlight etc.
The "take with meal" instruction is common with substances requiring fat for absorption/bioavailability. Dietary fat increases vitamin D3 absorption [5].
[3] https://pubmed.ncbi.nlm.nih.gov/28652922/ The relationship between serum vitamin D levels and sleep quality in fixed day indoor field workers in the electronics manufacturing industry in Korea
Friendly reminder: vitamin D3 can affect sleep if taken later in a day. I tend to skip if I forget to take it before noon. Also, D3 without additional K2 may lead to calcium excess.
Putting aside a potential common benefit coming from doing so, I'm having trouble morally justifying testing someone's blood for other purposes than it was explicitly given for.
Apart from security implications I can see multiple privacy issues here. Apple's services may attempt connections to non-Apple resources as well as Apple's.
My understanding is that trustd (Trust Daemon) will be allowed to report/validate (OCSP? CT?) certificates anywhere issuer points it to, and that nsurlsessiond (NSURLSession Daemon) will be allowed to attempt any connections other Apple processes will tell it to. From what I observed, opening a single podcast in Podcasts.app sometimes results in nsurlsessiond connecting to resources under multiple different domains.
My pessimistic view of today's techworld tells me to follow the money on this and that I might not be able to block in-system ads in some future.