This'n for example:
Reading a very little way into the story, I find that it's a vitamin D deficiency that's associated with dementia. Not the vitamin, a paucity thereof.
So, no pressing need to shield my skin further from the ravages of the Yellow Face, nor to discontinue the supplements during the dark season. Quite the opposite, in fact. Staying pale like Gollum could lead to thinking like Gollum.