If you’re one of the millions of Americans who want to live a healthy lifestyle, you’ve probably heard about all the lettered vitamins that your body needs on a regular basis. Vitamin A, vitamin B, vitamin C, vitamin D, vitamin E, and more like them can help improve your health in different fashions.

According to a study from 2011: “It is now clear that vitamin D has important roles in addition to its classic effects on calcium and bone homeostasis. As the vitamin D receptor is expressed on immune cells (B cells, T cells, and antigen-presenting cells), and these immunologic cells are all capable of synthesizing the active vitamin D metabolite, vitamin D has the capability of acting in an autocrine manner in a local immunologic milieu.” And perhaps most telling of all: “Vitamin D can modulate the innate and adaptive immune responses.”

But what, exactly, does that mean for you and your health?

Your body is better equipped to fight diseases

A person’s immune system essentially functions like an army that’s trained to sniff out unwelcome intruders, or diseases. Vitamin D provides that army with the cavalry and the weaponry to fight back. A lack of fighting materials- namely, soldiers and ammo- leads to an army that can easily be overtaken, and by the same token, a lack of vitamin D means that your immune system is much less likely to be able to fight off illnesses that may invade the body.

This means your chances of getting sick are reduced

Though nothing is truly guaranteed to provide your body with a foolproof defense mechanism against diseases (after all, nothing is truly guaranteed in life, is it?), vitamin D is definitely one of your best bets to reduce the possibility of catching a virus. Of course, viruses can still attack and enter your body no matter how much vitamin D you have in your system, and you may feel under the weather as a result. But the chances of actually becoming too sick to function in your daily life are drastically diminished. In addition, if you do start feeling sick, the odds are that the vitamin D will activate the T cells in your body so that they ward off the unfamiliar pathogens quickly, which will result in your under-the-weather feeling not lasting nearly as long as it otherwise would.

Vitamin D and T cells are best friends!

The science behind how vitamin D can help improve your immune system focuses on T cells, the components of your body that do the actual fighting against diseases. The presence of a great enough quantity of vitamin D helps stir the T cells to life and dispatches them to fight against foreign pathogens. Though your body can actually produce vitamin D by itself, the amount that your body can produce naturally isn’t always enough to be effective- and that’s where elderberry products come in, supplementing the naturally-made vitamin D with some reinforcements.