Vitamin D supplements can raise your serum levels well beyond what you can get from sunshine. You really need to get your blood tested to figure out your dose.

> My questioned is motivated by the common knowledge that vitamins tend To be flushed through out of the body during urination.

That's true for Vitamin C but probably not for most vitamins, they are all quite different. Vitamin A for instance can accumulate to hazardous levels and take a long time to go back to normal.