Not All Vitamin D Is Created Equal Vitamin D is crucial for your immune system, bone health, and even mood and cognition. Surprisingly, most Americans are deficient in the total body-health supporter — don’t be one of them.† Vitamin D Benefits Vitamin D is needed at every level for whole-body health. In fact, every single type of tissue in your body has receptors for Vitamin D. Your bones, heart, brain, muscles, immune system, you name it, all require sufficient Vitamin D to function optimally. Vitamin D is also the only vitamin that also functions as a hormone in the body, making it even more important to be sure you are not deficient or insufficient in this all-important micronutrient.