The global coronavirus pandemic definitely left people wondering how to keep themselves well. You know that social distancing, working from home and staying inside in general is one way to protect yourself -- but are there other measures you can take? Boosting your immune system is one of the best things you can do because it is your body's key defense when it comes to fighting a virus. Even if you are exposed to a virus, the coronavirus or others, if your immune system is strong, you have a better chance of not getting sick. Vitamin C is a popular choice for supporting immunity, but another key nutrient for your immune system is vitamin D. Once thought as the vitamin for strong bones, vitamin D actually does a lot more for your body -- including support your immune system. Studies suggest that vitamin D can help prevent respiratory infections or reduce the severity of them, especially if you have a deficiency. They jury's out on how exactly it can protect you from the coronavirus, but some medical experts recommend taking a vitamin D supplement to help boost your immune system. Below, Jacyln Tolentino, a physician at Parsley Health in Los Angeles, explains how vitamin D works, how to get enough of it, what happens when you have a deficiency and if it can help protect your immune system. Why is vitamin D important? Vitamin D is unique because it's one of only two vitamins that your body can produce on its own (the other is vitamin K), and you can also get it from other sources like food or supplements. It's also technically a hormone that regulates how much calcium is in your blood. Unlike other vitamins, it requires conversion in the liver and kidneys to make it an active hormone. "Vitamin D is a fat-soluble vitamin that our bodies use to absorb and maintain healthy calcium and phosphorus levels, which are necessary to grow and maintain our bones," Tolentino says. You've probably heard that vitamin D is important for your bones, but it supports your body in other ways, too."While we generally associate vitamin D with musculoskeletal health, it actually has several functions in the body, including the role it plays in immune function and reducing inflammation," Tolentino says. Vitamin D and immune health Research shows that vitamin D plays an important role in immune function, and a deficiency in it is shown to increase your susceptibility to infection. "Some studies have shown that vitamin D deficiency is even associated with greater risk of self-reported upper respiratory tract infections," Tolentino says. Further, "low serum levels of calcidiol [a form of vitamin D]  are also associated with higher susceptibility to infections like tuberculosis, influenza, and viral infections of the upper respiratory tract," Tolentino says. One of the main functions of vitamin D is to help activate T cells, aka the "killer cells" in the body. T cells actually detect and destroy foreign pathogens -- like viruses. "That makes vitamin D especially crucial for maintaining a functioning immune system that's capable of fighting back foreign pathogens," Tolentino says. It's important to know that although the coronavirus does affect the respiratory system, researchers and doctors know little about how vitamin D affects your risk of catching COVID-19 at this time. The best ways to reduce your risk of being infected with the coronavirus is to follow CDC and WHO guidelines, what your local officials say and to take care of your health as much as you can overall. Vitamin D is known to help the immune system, which is promising for protecting you from many different types of illness. Why people need a Health Adviser: Change to “The Nutra Seasons cGMP Promise” Every Nutra Seasosns product is manufactured in a state of the art cGMP certified manufacturer. Ingredients are tested both before and after the manufacturer process to ensure complete safety and optimal effectiveness.