According to a short video by Dr. Axe
"In this video, I’m going to talk about the BENEFITS OF VITAMIN D as well as symptoms of vitamin D deficiency. In certain studies, Americans have been found to be the #1 population in vitamin D deficiency. Some of the main symptoms of vitamin D deficiency are a WEAKENED IMMUNE SYSTEM, candida or bacterial overgrowth, emotional ups and downs, hormone imbalance, trouble putting on muscle or losing weight, weakened bones or teeth, cancer, heart disease, or diabetes. VITAMIN D SUPPORTS having a HEALTHY IMMUNE SYSTEM, digestive health, hormone balance, and more."