The process of turning the food that we eat into substances that the body can use is a complex chemical process that occurs throughout the digestive system and in the body itself. A slew of chemical substances help break down or create the carbohydrates, fats and proteins we need to live. The first of these to be discovered, and some of the most vital to our health and well-being are called vitamins.
The University of Maryland Medical Center defines vitamins as "a group of substances that are essential for normal cell function, growth, and development." There are 13 which are considered essential, and they fall into two categories. Some are fat soluble, which means that they can be stored in the body. Other vitamins are water soluble, which means that they must be used right away by the body or they will be excreted in urine.
The four fat soluble, or storable, vitamins are:
Vitamin A. The most common form of this vitamin is retinol, found in meat, especially liver. The vitamin is important for eyesight and for "healthy skin, teeth, skeletal and soft tissue, mucus membranes, and skin." It can be toxic in large amounts. The body can also produce vitamin A from beta-carotene which may be found in vegetables and fruits. Beta-carotene is not believed to be toxic.
Vitamin D. The body produces vitamin D through exposure to sunlight. It is used to help the body absorb calcium, which is important for bone health as well as regulating the heart's electrical system. Few foods contain this vitamin so it is often added, with milk being a noteworthy fortified food. Lack of vitamin D in poor nations and in the past in the United States produced a bone condition called rickets. Too much vitamin D can cause the body to retain toxic levels of calcium.
Vitamin E. This vitamin is an anti-oxident, important to protecting the body's systems from substances called free radicals. It plays a part in strengthening the immune system and also the formation of red blood cells. While at least eight similar compounds are known as vitamin E, only alpha-tocopherol "is recognized to meet human requirements." Often touted as a treatment for heart disease, cancer or other serious medical conditions, the current studies have generally failed to support such claims. The vitamin, in large quantities, may interfere with some medications, including statins.
Vitamin K. In order for blood to clot, the body must have an adequate supply of vitamin K. In the United States, the standard of care for newborn babies is to give them an injection of the vitamin to prevent vitamin K deficiency bleeding. While the condition is rare, studies have shown that newborns are often lacking a sufficient stored supply of the vitamin for up to three months after birth. Patients on blood thinners after a stroke or heart attack are cautioned about taking supplements of this vitamin, since it will interfere with the proper action of the medication.
Vitamin D can be manufactured in sufficient quantity by the body with just three outings in the sun, of 15 minutes each, per week. The National Institutes of Health state that the best source of the other three vitamins is food. A proper diet and a little sunshine will keep the body well supplied with the four fat soluble vitamins.