One B vitamin called thiamin does in large doses seem to change a person’s body odor. But there seem to be inconsistent results as to its effectiveness at repelling mosquitoes. The reason it seems to change body odor is that some excess thiamin is excreted through the skin. Most excess thiamin, however, is excreted in the urine. As to its ability to repel mosquitoes, I don’t know.
I would not suggest you take megadoses of thiamin for a bug repellent. A megadose of a nutrient is more than 10 times your Recommended Dietary Allowances (RDA) for that nutrient. Large quantities of one nutrient may cause a deficiency of another nutrient. Copper and zinc are two such nutrients.
Most excess water-soluble vitamins (B and C), are excreted in your urine. We know that high doses of vitamin C (1,000 milligrams or more) acidifies the urine, elevates the amount of oxalate in the urine and may lead to the formation of stones in the kidneys or bladder. We don’t know everything about all vitamins yet. Use caution when popping daily supplements.
Absorption from vitamin and mineral supplements is usually low. Some estimates are 10 to 15 percent from a vitamin pill. The rest goes down the toilet. For what some people spend on vitamin and mineral supplements, that is some pretty expensive urine.