Amanda Clark, MA, RN.
Deputy Editor, Professional Nurse....
Vitamins are complex chemical substances that are not manufactured by the body itself and must therefore be taken by dietary methods (BMA, 1997). This is the case with all vitamins except vitamin D, which is produced in the body when the skin is exposed to sunlight. Their role within the body is not fully understood, but the majority of vitamins have been found to act on one or more of its systems or functions. A deficiency of any one of these essential chemicals can lead to an illness or disease specific to the vitamin concerned (Trounce and Gould, 1997). Vitamins are either fat- or water-soluble. Table 1 discusses vitamin sources, uses and deficiency problems.
Fat-soluble vitamins are absorbed, together with fat from the intestine, into the circulation. Any disease or disorder that affects the absorption of fat, such as coeliac disease, could lead to a deficiency of these vitamins. Once absorbed into the circulation these vitamins are carried to the liver where they are stored. Fat-soluble vitamins include A, D and K.
Water-soluble vitamins, such as Vitamin C and the B vitamins are stored in the body for only a brief period of time and are then excreted by the kidneys. The one exception to this is vitamin B12, which is stored in the liver (Trounce and Gould, 1997). Water-soluble vitamins need to be taken daily.
The recommended daily requirements for men, women and pregnant or breastfeeding women are shown in Table 2. These requirements should be easily met if a balanced diet is adhered to; however, there are groups that may be at greater risk of developing vitamin deficiencies than others. These include those on restricted diets, patients who have digestive disorders that affect the absorption of fat, patients on lipid-lowering medication and those whose dietary choices are affected by financial or for conscientious reasons (Trounce and Gould, 1997). For these groups there may be advantages in taking a general or specific vitamin supplement following advice from a GP or nutritionist. However, for those on a balanced diet there is little to be gained from taking additional vitamins (NHS Direct Online, 2003).
British Medical Association. (1997)The British Medical Association New Guide to Medicines and Drugs. London: Dorling Kindersley.
NHS Direct Online. (2003)Nutrients. Available at: www.nhsdirect.nhs.uk
Trounce, J., Gould, D. (1997)Clinical Pharmacology for Nurses. London: Churchill Livingstone.