Vitamins are organic, non caloric micronutrients that are essential for normal physiologic function. Vitamins must be consumed through food with only THREE exceptions; Vitamin K & biotin can also be produced by normal intestinal flora (bacteria that live in the intestines & are critical for normal gastrointestinal function) & vitamin D which can be self produced with sun exposure.
No “perfect food” contains all the vitamins in just the right amount; rather a variety of nutrient dense foods must be consumed to assure adequate vitamin intakes.
Many foods such as bread and cereals have been fortified with some nutrients to decrease the risk of vitamin deficiency. And some foods contain inactive vitamins – called – PROVITAMINS. Fortunately, the human body contains enzymes to convert these inactive vitamins into active vitamins.
Humans need 13 different vitamins, which are divided into two categories, WATER SOLUBLE VITAMINS and FAT SOLUBLE VITAMINS.
THIAMIN, RIBOFLAVIN, NIACIN, PANTOTHENIC ACID, FOLATE, VITAMIN B6, VITAMIN B12, BIOTIN & VITAMIN C – are all water soluble vitamins. Their solubility in water (which gives them similar absorption and distribution in the body) & their role as COFACTORS of enzymes involved in metabolism (i.e. without them the enzyme will not work) are common traits.
With the exception of vitamins B6 and B12 water soluble vitamins cannot be stored in the body and are readily excreted in the urine. This decreases the risk of toxicity from overconsumption and also makes their regular intake a necessity. Folate (vitamin B9, also known as folic acid in its supplement form) named for its abundance in plant foliage (like green leafy vegetables) – deserves a special mention due to its crucial role during pregnancy. Folate is essential for the production of DEOXYRIBONUCLEIC ACID (DNA), red and white blood cell formation, neurotransmitter formation and amino acid metabolism. Deficiency is relatively common, as folate is easily lost during food preparation and cooking and because most people do not eat enough green leafy vegetables.
Vitamins A, D, E & K are FAT SOLUBLE VITAMINS. Often found in fat containing foods and stored in the liver or adipose tissue until needed, fat soluble vitamins closely associate with fat. If fat absorption is impaired, so is fat soluble vitamin absorption. Unlike water soluble vitamins, fat soluble vitamins can be stored in the body for extended periods of time and eventually are excreted in the faeces. This storage capacity increases the risk of toxicity from overconsumption, but also decreases the risk of deficiency.
Choline, called a quasi-vitamin because it can be produced in the body but also provides additional benefits through consumption from food, is also important since it plays a crucial role in neurotransmitter and platelet function and may help to prevent Alzheimers disease.
A list of vitamins, common food sources, & functions can be found here.