When I was younger, the vitamins that parents used to give to their children is in the form of liquid. Nowadays, they do have it in the form of candies or gummy bears which makes taking vitamin more fun and enjoyable. People with low immune system should consider taking liquid vitamin D3. It's more beneficial to them rather than taking pill vitamins. According to Wikipedia, Vitamin D3 or cholecalciferol which is also known as toxiferol, is structurally similar to steroids such as testosterone, cholesterol, and cortisol. You c an read more about Vitamin D3 by visiting the link I have provided.