What do you mean by "[not] regularly"? Do you eat fortified food instead? If you don’t like the daily intake have you considered the weekly and two-weeks intake ?

Everybody make his own choice so I won’t tell you what to do and as you’re vegan since a long time you already know the danger of B12 deficiency but just in case here’s some documentation. Test for MMA, not B12 (it’s far more reliable).

https://www.vegansociety.com/resources/nutrition-and-health/...

Cool. It's the most well-known concern. The side-effects of deficiency are pretty terrible, including depression and neuropathy. While there were many happy and healthy vegans in my college's dorm many moons ago, there was one vegan guy who was definitely deficient based on mood (severe depression) and appearance.

Glad you're not contributing to (bacterial) antibiotic resistance, (viral) pandemics, climate change, resource inefficiency, air/water/soil pollution, or animal cruelty as much as the rest of us. I'm merely a lazy vegetarian.

Vitamin D is fat soluble, so overdosing is very possible. 4000 IU (100 µg) is the average tolerable upper limit (UL). I'd get checked for kidney stones too, which are possible with Vitamin D, calcium, and Vitamin C overdoses.

At unmitigated baseline, I'd be chronically Vitamin A, iron, and B-12 deprived. I have to take more than the UL of each, but the amounts are periodically recalibrated by blood tests. I have ginormous kidney stones that will eventually need to be removed.

When taking "a lot" of Vitamin D, one should also take an adequate amount of Vitamin K2 and Magnesium. They work synergistically and will prevent leaching of calcium into the bloodstream.