Vitamins, What Are They and What Do They Do?

Decades of aggressive advertising have convinced many Americans that they need to take a daily vitamin pill to remain in good health. Yet, few people can accurately describe the role vitamins play in a healthy diet.

Vitamins are essential biochemicals needed in very tiny quantities to catalyze metabolic reactions. For example, Vitamin K starts the process that allows blood to clot, thus preventing a person from bleeding to death if they are cut or severely injured. Many of the B vitamins are needed to synthesize body proteins and burn calories. Key functions vitamins perform can be divided into three main areas.

Energy metabolism- Vitamins help convert the calories in food into useable energy and store surplus energy as glycogen or fat.

Tissue Synthesis- Vitamins are required to manufacture all the cells in the human body, including immune system, bone, and blood cells.

Antioxidants- Vitamins protect body tissues from oxidative damage by functioning as antioxidants.

The first vitamins identified contained a nitrogen-rich amine group as part of their chemical structure. When scientists recognized the importance of these amine-containing compounds to health, they called these new substances ‘vital amines.’ The word ‘vitamin’ is a contraction of this term.

Eating either too little (deficiency) of too much (excess) of any one vitamin interferes with that vitamin’s key functions and can cause characteristic diseases and symptoms.

Fat- vs. Water-Soluble Vitamins

Scientists and health experts group vitamins into two broad categories based on whether they dissolve in fat/oils or in water. Knowing the solubility of a vitamin provides clues as to which foods are likely to supply it, how vulnerable it is to loss or destruction during cooking, and its toxic potential if consumed in excess.

Fat-Soluble Vitamins: The fat-soluble vitamins are A, D, E, and K. They are stored in body fat and, thus, can reach toxic levels if consumed in excess. Fat-soluble vitamins are more heat resistant and, thus, less likely to be damaged during cooking than water-soluble vitamins

Water-Soluble Vitamins: The water-soluble vitamins are the B complex vitamins (such as niacin, thiamine, folate, B₁₂) and vitamin C. As a general rule, water-soluble vitamins are easily excreted from the body so they are less likely to be toxic. However, in some instances, people who use too many supplements have developed symptoms of vitamin C and B₆ toxicity. Consuming 10 times the recommended amount of vitamins C and as little as four times the recommended amount of B₆ can produce toxicity symptoms.

Toxicity symptoms have also been observed in people consuming large amounts of niacin to lower their blood cholesterol, but in these cases, the people were consuming 100 times or more the normal amount of niacin. Water-soluble vitamins can be lost during cooking due either to destruction by heat or by leaching into cooking water.

Vitamins are released from food during digestion, but because digestive enzymes can’t attack them, the vitamins themselves are not digested. Water-soluble vitamins pass easily through the intestinal lining into the blood stream. They circulate throughout the body in the water-based plasma portion of blood.

Typically, the kidneys remove excess amounts of water-soluble vitamins from the blood stream. Fat-soluble vitamins, on the other hand, must be transported through the body attached to specialized carriers. They tend to accumulate in the body’s adipose (fat) tissues. As a general rule, because fat-soluble vitamins are stored in the body, whereas water-soluble ones can be readily eliminated, fat-soluble vitamins have a much greater potential to reach toxic levels than water soluble vitamins.

Finding Vitamins in Food

With the possible exception of specially fortified breakfast cereals, no one food is a good source of all vitamins.

Every food group indicated on the Food Guide Pyramid contains a different array of essential vitamins. The fruit and vegetable groups are good sources of vitamins A, C, K, and the B complex vitamin folate. Grains provide other B complex vitamins like thiamin, niacin, and vitamin E. Meats and meat substitutes provide additional B complex vitamins, most notably thiamine, niacin, and B₁₂, egg yolk and organ meats like liver also provide vitamins A and D. Milk is the best natural source of the B complex vitamin riboflavin. Fats, oils, nuts, and seeds are good sources of vitamin E.

To prevent common vitamin deficiencies, the United States Department of Agriculture (USDA) requires some foods be enriched or fortified with specific vitamins. For example, white flour is enriched with the B vitamins lost when the bran is removed during processing. Flour is also fortified with the B vitamin folate-occurring naturally in oranges, green leafy veggies, and proteins but not grains-to prevent a common and serious birth defect called spina bifida or neural tube defect. The decision to fortify white flour products with folate was made because most people eat products made with this ingredient. Similarly, milk is fortified with vitamins A and D, which work in concert with the calcium in milk to improve bone health.

Enriched- replacement of vitamins or minerals removed during processing

Fortified- adding more vitamins or minerals than were originally present in the unprocessed version of the food

Vitamins Produced by the Human Body

The human body is capable of making a few of the vitamins it needs each day if it is given the right building blocks. For example, vitamin A can be made from the yellow-orange plant pigment beta carotene, which is present in carrots, cantaloupe, winter squash, dark leafy greens, and broccoli. The B complex vitamin niacin (also known as B₃) can be made from the amino acid tryptophan. Vitamin D can be synthesized when a cholesterol-like compound found in human skin is exposed to sunlight, and bacteria living in our large intestine can produce some of our daily vitamin K requirement.