Did you know that 40% of adults in the United States are vitamin D deficient? Vitamin D, sometimes referred to as the "sunshine vitamin", is an essential nutrient for supporting bone health and the immune system. Symptoms of vitamin D deficiency include fatigue, depression, muscle weakness, and more. The good news is that once detected, vitamin D deficiency is easy to treat with supplementation and/or sunlight exposure. Keep reading to find out more about the "sunshine vitamin" – and the many ways it can impact your health – and learn more about our Vitamin D Test.