Vitamin D Found to Boost Immunity New study discovers that 'sunshine vitamin' activates T-cells By Kevin Spak, Newser Staff Posted Mar 8, 2010 8:07 AM CST 6 comments Comments Milk and sunlight are two of the main ways people acquire vitamin D. (Shutterstock) (Newser) – Taking in some sunshine is vital for your immune system, according to a new study released yesterday. A group of Danish researchers have discovered that infection-killing T cells rely on vitamin D to activate, Reuters explains. “If the T cells cannot find enough vitamin D in the blood, they won’t even begin to mobilize,” says the study’s lead author. Scientists have long known that vitamin D, which the body produces when skin is exposed to sunlight, helped stave off cancer and multiple sclerosis. “What we didn’t realize is how crucial vitamin D is for actually activating the immune system,” the lead researcher explains. Nearly half the world’s population has less-than-optimal vitamin D levels, according to some studies, and that number is growing as people spend more time indoors.