Alice Branton explains that Vitamin D is critical for overall health, not just for strong bones as commonly believed. It is needed for all other vitamins to work properly and is compared to the electricity that powers a home. A deficiency in Vitamin D can lead to various health issues including cancer, inflammation, stress, hormonal imbalance, and immune disorders. She also debunks the myth that Vitamin D is only needed for bone health and growth, stating that it is needed for every cell in the body. She says that most supplements are not bioavailable and that Vitamin D is present in very small amounts in food. Drinking milk alone is not sufficient to meet the body's Vitamin D needs.