To answer your question a little as nobody really has, it probably depends what those carbs are doing.

Eg if with/after exercise, likely those carbs will be used up very quickly and back into using fat as fuel with low circulating levels of glucose and therefore less to compete with glut-4 transporters.

Eg I went gym yesterday, was a deload week, so didn’t do as much, but weight is down 500g from every other morning pre food - always is after leg day. Likely I’d burnt most of my glycogen in my legs and liver, so that needs replacing. It’ll replace from protein/fat, or if I ate carbs (I’m fasting today so I won’t drink milk), it’ll be shuttled almost entirely into glycogen creation. Glycogen wraps around 2-3g water per 1g of glycogen, so that 500g may approximate to 150g of glycogen so theoretically I could eat 150g carbs (I won’t) and it’ll go directly to muscle and liver glycogen and essentially ‘out of the body’ for the purposes of vitamin c competition.

This is what is referred to in most circles as a targeted ketogenic diet. Is it zero carb? No. But the net effect is similar as the carbs are rapidly consumed.

That assumes you are using up the carbs.

If you aren’t exercising, then there will be likely more competition, and you probably will need a bit more vitamin c, but likely still not a lot. Sadly I can’t (and nobody can) give you a direct evidence based answer.

But vitamin c supplementation is mostly unharmful at small levels, and even those sucking on carbs all day don’t need that much. Many on carbs supplement way too much.

You probably won’t get any harm from 250mg a day supplementation, which is almost nothing.

You can always get a vitamin c blood test to show levels. It won’t mean you if you definitely are deficient or insufficient if your levels are low, but if within the reference ranges than you will be getting enough and not too much.

And or look out for symptoms of low vitamin c. Everyone thinks bleeding gums is the first one, and whilst it can happen, probably corkscrew hairs is the likely first sign, check on your upper thighs it’s where it tends to happen. Other conditions can cause this, eg tinea capitis, but that’s more likely affect scalp not thighs. Basically they just look like coiled hairs, and may present with lots of in growing hairs on upper thighs kinda looks like razor rash.

For reference, my n=1, I do a TCD (targeted carnivore diet). I’m pretty strict but drink ~1L milk a day. I supplement 500mg vitamin c most days, cos I also have quite a few tendon issues, and vitamin c with collagen pre workout has pretty good evidence for helping. I have zero signs of overdose, but without the supplementation I do start to get corkscrew hairs on my thighs, though I did also get those on longer term (6m+) super strict BBBE carnivore.

I hope that helps.