Lack of D wouldn't be good for the brain. Symptoms of Shortage could be bone pain, muscle weakness, fatigue, cardiovascular disease, asthma etc but those are things you would notice.
(Title: The ongoing torture and medical neglect of Julian Assange)
In a recent story, D3f4ult discussed that this happened to him for a year and he was given 24/7 isolation for one year. [2]
[1]: https://solitarywatch.org/facts/faq/ [2]: https://journalistsresource.org/home/solitary-confinement-re... [3]: https://darknetdiaries.com/transcript/139/
it is completely about barbarian, punitive, punishment. it doesn't work, but it makes many of us feel good, so we continue doing it.
I once had to do a deposition with a warden, so I asked him straight out how they got away with this. His answer was "math". Basically he said "Look, jails are short term facilities, the average stay here is 30 days. Nobody is going to come to harm in 30 days."
The problem with the word "average" is that it is very misleading. When say 50% of those arrested are able to bail out within hours, that brings the average down considerably, compared to the other significant part of the population who have been in there up to 11 years waiting for trial.