Alice explains that Vitamin D is critical for immunity, cardiac health, and cognitive health, and a deficiency can lead to various health issues including cancer, Alzheimer's, and autism. Despite being known as the sunshine vitamin, Alice states that simply being in the sun is not enough to maintain adequate Vitamin D levels, as many people are unable to effectively convert sunlight into Vitamin D. She also debunks the myth that taking a supplement or consuming Vitamin D-rich foods is sufficient, as most nutraceuticals are not bioavailable and only small amounts of Vitamin D are found in food and emphasizes the need for bioavailable sources of Vitamin D.