Let’s take a closer look at vitamin D and immune support, though, especially when it comes to T cells. For instance, vitamin D is a powerful immune system supporter and inhibits negative autoimmune responses by modulating T cell responses. When vitamin D is in short supply, Th1 cells can attack the body instead of fighting off unwanted invaders.

That’s great, but what exactly are T cells? T cells are types of white blood cells that are of high importance to the immune system, particularly how the body tailors its immune response to specific invaders such as viruses and bacteria. T cells, in fact, are likened to soldiers that seek out and destroy targeted invaders.

The University of Copenhagen published their findings about T cells and vitamin D in Nature Immunology. The researchers report that it appears vitamin D activates the body’s T cells, which act as the immune system’s first defense against viral and bacterial invaders.

“When a T cell is exposed to a foreign pathogen, it extends a signaling device or ‘antenna’ known as a vitamin D receptor, with which it searches for vitamin D,” Carsten Geisler, the study’s lead author, told Reuters.

The researchers indicated that if someone comes up short on vitamin D—and about 75% of U.S. teens and adults and half the world’s population are deficient in vitamin D—T cells won’t become activated and respond to unwanted invaders. Additionally, the researchers believe that their findings can have all sorts of health implications—“from common viruses to combating global epidemics,” they say.

Dr. Michael Holick, professor of medicine at Boston University and the world’s leading authority on vitamin D, says, “Every tissue and every cell in your body has a receptor for vitamin D. Every tissue and every cell of your body requires vitamin D to function properly. We’re now recognizing that immune cells in the body have vitamin D receptors, which means that they need vitamin D to fully function. And we’re now recognizing that the immune cells that gobble up many immune-threatening elements are controlled in part by vitamin D.”

That’s great news in and of itself, but what’s more is that vitamin D is cost effective.

“The cost of a daily dose of vitamin D3 is less than five cents, which could be balanced against the high human and economic cost of cellular unhealth attributable to insufficiency of vitamin D,” researchers point out.

Dr. Greg Plotnikoff, Medical Director, Penny George Institute for Health and Healing, Abbott Northwestern Hospital in Minneapolis says, “Because vitamin D is so cheap and so clearly reduces all-cause mortality, I can say this with great certainty: Vitamin D represents the single most cost-effective health benefit in the United States.”

Apparently so—and now strong T cell function is just one more reason why we don’t want to come up short on the sunshine vitamin.