Vitamin D is a fat-soluble vitamin. It’s also known as the sunshine vitamin because we produce most of what we need through exposure to the sun. We also get some vitamin D from our food. Vitamin D controls how your body absorbs calcium and phosphate. It’s vital for keeping your bones, teeth, and muscles healthy, and plays a role in immune function and mental health. If your Vitamin D levels are low, you might feel tired, get sick often, have weak bones, and feel anxious or depressed.