Vitamin D supplements may improve exercise performance and lower the risk of heart disease. Researchers say that vitamin D can block the action of an enzyme called 11-ßHSD1, which assists in making the stress hormone cortisol. Elevated levels of this hormone can increase blood pressure by restricting the arteries, narrowing blood vessels, and encouraging the kidneys to retain water. Thus, researchers theorize vitamin D could improve exercise performance and lower risk factors for cardiovascular issues by reducing cortisol levels.
Society for Endocrinology Annual Conference, November 2015