There is a lot of research that exists on vitamin D, particularly in relation to depression, autism, seizures, and a host of other neurological manifestations, that supposedly stem from having low vitamin D levels. Referred to as the 'sunshine' vitamin, vitamin D is a fat-soluble (can be stored in the body) and its main function is to promote calcium and magnesium absorption in the gut. I won't go into the specifics, as they can be explained much more thoroughly on this site than I could ever do justice.
I have always maintained a certain level of skepticism with vitamin D, since to me, it really isn't a vitamin at all - it's a steroid, that ultimately can affect hormone levels in the body, which in turn affect the entire equilibrium of the endocrine system. Touting vitamin D as the savior for combating all of these different illnesses raises a number of questions for me and there is certainly an endless amount of literature to address my inquiries. Just search through Pubmed and you will discover enough reading for all of 2017. Vitamin D is implicated, in terms of epilepsy alone, in everything from hypocalcemia to influences on AEDs.
Vitamin A on the other hand is a bit of an anomaly when it comes to the implications on seizures and autism. Vitamin A is also a fat-soluble vitamin, nearly synonymous with, on every single health website imaginable, the word 'vision'. While its importance to the cornea cannot be ignored, the vitamin's influence on other organs should not be understated. Just like vitamin D, vitamin A can also influence hormones.
So what is the potential connection between D + A? I have been asking this same question, as I have gone through a ton of anecdotal stories regards the efficacy of both vitamins, on seizures and autism. Some medical professionals have even gone so far as to develop a high dosage protocol for the treatment of autism in particular, for both vitamin D and vitamin A. There are message boards that have extensive threads on this very subject, most of which reference one single source: The Vitamin D Council, which is less of a populated 'council', as it is the compiled research of one person, Dr. John Cannell, and you should note with full disclosure, he specifically endorses one particular brand of vitamin D, developed by Biotech Pharmacal. I'm not sure exactly why this particular balance of vitamin D3, vitamin K2, magnesium, zinc, and boron are considered an exclusive proprietary blend that they need to be endorsed, with Cannell potentially being compensated for, as there are hundreds of supplements on the market, but I digress. Regardless, Dr. Cannell's commitment to researching the effects of vitamin D should not go unrecognized. His agenda seems very simple - most of the general population is deficient in vitamin D and everyone who is deficient, should be supplementing to some degree. In terms of vitamin A, no such council exists as far as I can tell, thus there is no single unified source of literature to comb through.
There are connections between D + A and they revolve around the mechanism of action. The one that I started focusing on was the idea that both vitamins can influence voltage-gated calcium channels (VGCCs). You've probably heard me mention this in the past, as VGCCs are the supposed mechanism of action of Lyrica (pregabablin) which is a medication that Mira has been on for years. The function and pharmacology of VGCCs are nicely organized in chart here, which as you will read, influence everything from nerve terminals to endocrine cells. VGCCs have been the focus for therapeutic studies for some time - here is an extensive technical paper on the subject. If vitamin D can affect the 'fluidity' (so to speak) of VGCCs, are there antagonists that do the exact opposite? As it turns out, there has already been some research regarding the antagonistic relationship between vitamin A and vitamin D. I also found a great article that highlighted the concerns of excessive or even additional supplementation of vitamin D in relation to autism, from more of a historical perspective.