According to a study presented in Edinburgh, U.K. noted that taking vitamin D3 can improve exercise performance and lower your risk of heart disease. In addition, there were a number of other benefits.
Adults taking vitamin D had lower blood pressure compared to those given a placebo, as well as having lower levels of the stress hormone cortisol in their urine. This is the hormone associated with stress.
On a personal level, both with self and working with patients, I have noted and seen improvement in terms of overall endurance.