Vitamins are required for normal growth, metabolism and good health. Their task is to metabolize other nutrients to provide energy and start reactions in the body. They are found in fruits, vegetables and other food, but may be missing due to a number of reasons. The USDA (United States Department of Agriculture) recommends a bare minimum requirement of vitamin supplements to prevent deficiencies.

There are two kinds of vitamins classified according to their solubility. The fat soluble vitamins are A, E, D and K, and can be stored in the body. They contain carbon, hydrogen and oxygen. The water soluble vitamins contain nitrogen, and sometimes sulfur, in addition to these three. Water soluble vitamins include vitamin C or ascorbic acid and vitamins of the B group: thiamine or vitamin B1, riboflavin or vitamin B2, niacin or vitamin B3, pantothenic acid or vitamin B5, pyridoxine or vitamin B6, biotin or vitamin B7, folate/folic acid or vitamin B9 and vitamin B12. They cannot be stored in the body.

It is important to be aware of the multiple functions of vitamins and effects of deficiencies to understand the role of vitamin supplements. Vitamins allow nutrients to be digested and absorbed and convert carbohydrates and fats into energy. They help to metabolize nutrients, produce antibodies to strengthen immunity and develop resistance to diseases. Vitamins strengthen cells, bind tissues, form bones, blood cells and genetic material, hormones and chemicals of the nervous system and combine with proteins to produce enzymes. Each group of vitamins performs more specific roles.

Vitamin A is essential for immunity, vision, bones, cells, reproductive health, skin and body linings. Vitamins of the B complex group are required for several body functions. Folate/folic acid is essential at every stage of life, as it is responsible for DNA, RNA and protein production. Vitamin C helps to build and maintain tissues, healthy bones, blood vessels and skin and strengthen immunity. Vitamin D controls the calcium levels in the blood and prevents bone loss, osteoporosis and auto immune diseases. It is essential for proper absorption of calcium and regulation of the rate at which it is excreted. Vitamin E performs protective functions; it stops tissue damage by free radicals and protects intracellular membranes. Moreover, it reduces the risk of jaundice and other liver related diseases and neutralizes the ill effects of the long term use of antibiotics. Vitamin K is responsible for metabolism of the bones and clotting of blood.

Deficiency of vitamins has serious consequences. Lack of vitamin A leads to night blindness, retarded growth of the skeleton and problems of the skin and gastrointestinal tract. Vitamin B1 deficiency causes leg cramps, muscular weakness, irritability and digestive problems. Mouth ulcers, inflammation of the tongue, weakness, low blood counts and dandruff are among the symptoms of lack of vitamin B2. Insufficient vitamin B3 causes pellagra, while a deficiency of vitamin B6 leads to skin problems, mental confusion and lowered immunity. Vitamin B5 is an antioxidant required for growth, reproduction and bodily processes, so a lack of it produces heart problems and depression. Inadequate vitamin B12 causes pernicious anemia, while scurvy and rickets are the main symptoms of a lack of vitamins C and D respectively. Vitamin E deficiency affects the nervous system and leads to weakness, vision related problems and loss of muscle mass. Finally, easy bruising and gastrointestinal bleeding are symptoms of vitamin K deficiency.

In view of the above, it is important to identify the circumstances when there can be a deficiency of one or more essential vitamins. Studies have shown that most adults are deficient in vitamins B6, B12, folic acid, vitamins D and E. The diet may not be balanced, and lacking in the required amounts of these vitamins. Those on a macrobiotic diet or weight loss program often lack a balanced diet. Even multivitamins may fail to supply the recommended daily allowance (RDA) of vitamins D and E, so these have to be taken separately. Moreover, nutrient levels are depleted by physically strenuous activities.

Some people are more vulnerable to dietary deficiencies due to a number of factors. This group includes people living alone, pre and post menopausal women and the elderly. The latter usually consume less milk and may also have limited exposure to the sun, both of which are sources of vitamin D. Vegetarians and particularly vegans could be missing vitamins like B12, which are largely found in dairy products and non-vegetarian food. Elderly people, specially vegetarians, often suffer from gastrointestinal disorders due to a restricted diet, and this hinders absorption of vitamin B12. Moreover, some kinds of medication also hinder vitamin B12 absorption from food. Vitamin B6 deficiency occurs among older adults, specially if the diet is of poor quality or restricted over a long period. Alcoholics are at greater risk, as alcohol leads to decreased absorption of the vitamin. Even a normal diet may lack the required amount of 2 mg, so supplements have to be taken. People averse to fruits and vegetables are prone to suffer from vitamin C deficiency, while calcium deficiency is likely if milk products are missing from the diet, due to conditions like lactose intolerance.