What’s your line of reasoning here, I’m being dim
They do eat liver, so they’re getting vit A. D is interesting because Inuit type people (whatever the politically correct term these days is, I’ve been told off for saying Eskimo and Inuit, when I mean no disrespect at all, I just want to refer to those circumpolar native type tribes) actually have different vitamin D metabolism. So its hard to draw conclusions on vitamin D from them because deficiency doesn’t seem to work in them like it does Caucasians
I was mostly going in on lactose intolerance angle.
Cheese, eggs, liver, and oily fish—such as salmon, sardines, trout, herring or mackerel—are all sources of it, however I imagine dairy is the easiest source. Halibut is popular in Greenland though, with Halibut oil being a source of vitamin A too. Fish-heavy cuisines would probably see it in much refused numbers if food was the sole factor. Fortified foods such as cereals and white grain usually provide 100% of your daily dose of Vit B. If you ate no dairy, fish, eggs, fortified grains, or liver, you'd probably be at risk of getting no Vit A, same for D.
This is less a risk for adults, but if you're an infant and you went through the aforementioned sensory overload as an infant, experience some damage, and then received zero of the vitamins or silence necessary for neurogenesis, your brain might show no overt damage but subtler forms of damage—such as unformed neurones or incomplete connections—will stick.
This seems like an insane pivot but it relates (assuming the child's food/drink consumption matters more than the mother's): breastmilk.
Surprisingly breastmilk can provide an infant with Vitamin A and B but not D. If you went down that rabbit hole you can find a correlation between breastfeeding and autism where the correlation is surprisingly negative. i.e. nations where children are breastfed for longer correlate with higher rates of autism.
Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect
Note: this correlation/causation doesn't account for Australia, Canada—this is why I don't put it solely on diet.
So contextually: get overstimulated (from noise, or extreme physical sensation (pain)), brain gets damaged, receive not enough necessary vitamin D, brain repairs all wrong and to slow.
In this context you could mitigate autism if you exposed your child to sunlight, but in certain environments--such as loud, urban environments--you'd just be exposing them to further stimulation and thus more damage. A mother in Cairo or Tokyo bringing their infant outside exposes them to traffic, chatter, foot traffic, etc. The same sort of stimulation I think contributes to it.
That said, you could fix a vitamin D deficiency by sticking your infant's cot next to a window.
But at the same time, you might live somewhere with sunlight abundance, which would, funnily too, explain Canada and Greenland.
So: vitamin deficiency in infancy + overstimulation in infancy.
Highest sunlight areas = ample sources of natural Vitamin D
However, not so much vitamin diversity (A or B) due to lack of development or dietary restrictions. (India, Somalia, etc)
Low sunlight areas = non-ample sources of natural Vitamin D
But has vitamin diversity. (Fortified grains and processed foods provide A and B)
I'll avoid going all the board autistic on this but you can draw all sorts of correlations.
TLDR: Vitamin deficiency in infants,
possible diet of the mother, and exposure to harsh or extreme forms of stimulus can all intersect and increase likelihood of autism.
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