Do not megadose vitamin D.

any amount above the RDA is useless to your body and your kidneys will have to process it. Sometimes this causes a buildup of a chemical that forms hard sharp crystals. These are kidney stones and they are painful AF.

(that said, low doses of vitamin D are great, especially in countries where there isn't a lot of fish oil in the diet. here in the States they add it to milk so most people are covered if they make pudding or have a bowl of cereal now and then.)