Most of us have been told to take our vitamins, but few people know why, and despite all the talk about them in modern culture, vitamins remain something of a mystery. Vitamins are organic substances, essential for maintaining life functions and preventing disease among humans and animals and even some plants. They are found in very small quantities in food; certain health specialists recommend taking vitamin supplements to augment the supplies in food, while others insist that a well-balanced diet provides all the vitamins that an ordinary person needs. Some vitamins, such as vitamin C and the B complex, are water-soluble, which means that they are excreted easily and must be ingested every day. Others, such as vitamins A, D, E, and K, are fat-soluble and therefore are retained in the body's fatty tissues. With such vitamins, there may be a danger of taking too much, but in the case of most vitamins, the greatest harm comes from not receiving enough. Vitamin deficiencies can be the cause of rickets, pellagra, and other diseases that have plagued the poor in the Western world and the third world in the past and in the present.