Nutrients absorbed by the body for regular biogenic activity are sugars, proteins, fats, minerals, and vitamins. The “vita” in “vitamins” refers to vital substances. While vitamins by themselves are neither an energy source or a part of the body, they are essential for life and act as a lubricant for other nutrients to work well. Vitamin deficiency causes illness. As almost all vitamins cannot be produced by the body, they need to be ingested through food.