Food provides energy (as calories) and materials called nutrients needed for growth and renewal of tissues. Protein, carbohydrate, and fat are the three major nutrient components of food. Vitamins and minerals are found only in small amounts in food, but are very important for normal function of the body. Fibre, found only in foods from plants, is needed for the digestive system to work well.
Proteins are vital for tissue growth and repair. The moderate amounts required can be found in meat and dairy products, cereals, and pulses.
Carbohydrates are a major energy source, and are stored as fat when taken in excess. They can be found in cereals, sugar, and vegetables. Starchy foods are preferable to sugar.
Fats are a concentrated energy form needed only in small quantities. They are contained in animal products such as butter and in the oils of plants such as corn and nuts.
Vitamins and minerals are found only in small amounts in food but are very important for the normal functioning of the body.
Fibre (non-starch polysaccharides) is the indigestible part of any fruit, vegetable, or food or product derived from plants. It is needed for a healthy digestive system. Fibre contains no nutrients but adds bulk to faeces.
During digestion, large molecules of food are broken down into smaller molecules, releasing nutrients that are absorbed into the bloodstream. Carbohydrate and fat are then metabolized by body cells to produce energy. They may also be incorporated with protein into the cell structure. Each metabolic process is promoted by a specific enzyme and often requires the presence of a particular vitamin or mineral.
WHY DRUGS ARE USED
Dietary deficiency of essential nutrients can lead to illness. In poorer countries where there is a shortage of food, marasmus (resulting from lack of food energy) and kwashiorkor (from lack of protein) are common. In the developed world, however, excessive food intake leading to obesity is more common. Nutritional deficiencies in developed countries result from poor food choices and usually stem from a lack of a specific vitamin or mineral, such as in iron-deficiency anaemia.
Some nutritional deficiencies may be caused by an inability of the body to absorb nutrients from food (malabsorption) or to utilize them once they have been absorbed. Malabsorption may be caused by lack of an enzyme or an abnormality of the digestive tract. Errors of metabolism are often inborn and are not yet fully understood. They may be caused by failure of the body to produce the chemicals required to process nutrients for use.
WHY SUPPLEMENTS ARE USED
Deficiencies such as kwashiorkor or marasmus are usually treated by dietary improvement and, in some cases, food supplements rather than drugs. Vitamin and mineral deficiencies are usually treated with appropriate supplements. Malabsorption disorders may require changes in diet or long-term use of supplements. Metabolic errors are not easily treated with supplements or drugs, and a special diet may be the main treatment.
The preferred treatment of obesity is reduction of food intake, altered eating patterns, and increased exercise. When these methods are not effective, and the body mass index (BMI) is 30 or more, an anti-obesity drug may be used.
MAJOR DRUG GROUPS
Vitamins are complex chemicals that are essential for a variety of body functions. With the exception of vitamin D, the body cannot manufacture these substances and therefore we need to include them in our diet. There are 13 major vitamins: A, C, D, E, K, and the B complex vitamins – thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), cobalamin (B12), folic acid, and biotin. Most vitamins are required in very small amounts, and each vitamin is present in one or more foods (see Main food sources of vitamins). Vitamin D is also produced in the body when the skin is exposed to sunlight. Vitamins fall into two groups, depending on whether they dissolve in water or fat (see Water-soluble and fat-soluble vitamins).
Water-soluble vitamins Vitamin C and the B vitamins dissolve in water. Most are stored in the body for only a short period and are excreted rapidly by the kidneys if taken in higher amounts than the body needs. Vitamin B12 is the exception; it is stored in the liver, which may hold up to six years’ supply. For these reasons, foods containing water-soluble vitamins need to be eaten daily. These vitamins are easily lost in cooking, so uncooked foods containing them should be eaten regularly. An overdose does not usually cause toxic effects, but adverse reactions to large dosages of vitamin C and pyridoxine (vitamin B6) have been reported.
Fat-soluble vitamins Vitamins A, D, E, and K are absorbed from the intestine into the bloodstream together with fat. Deficiency of these vitamins may result from any disorder that affects fat absorption (for example, coeliac disease). These vitamins are stored in the liver and reserves of some of them may last for several years. Taking an excess of a fat-soluble vitamin for a long period may cause it to build up to a harmful level in the body. Ensuring foods rich in these vitamins are regularly included in the diet usually provides a sufficient supply without risking overdosage.
A number of vitamins (such as vitamins A, C, and E) have now been recognized as having strong antioxidant properties. Antioxidants neutralize the effect of free radicals, substances produced during the body’s normal processes that may be potentially harmful if they are not neutralized.
A balanced, varied diet is likely to contain adequate amounts of all the vitamins. Inadequate intake of any vitamin over an extended period can lead to symptoms of deficiency.
A doctor may recommend vitamin supplements in various circumstances: to prevent vitamin deficiency in people considered at risk, to treat symptoms of deficiency, and in the treatment of certain medical conditions.
WHY THEY ARE USED
Preventing deficiency Most people in the UK obtain sufficient quantities of vitamins in their diet, and it is therefore not usually necessary to take additional vitamins in the form of supplements. People who are unsure if their present diet is adequate are advised to look at the table to check that foods that are rich in vitamins are eaten regularly. Vitamin intake can often be boosted simply by increasing the quantities of fresh foods and raw fruit and vegetables in the diet. Certain groups in the population are, however, at increased risk of vitamin deficiency. These include people who have an increased need for certain vitamins that may not be met from dietary sources – in particular, women who are pregnant or breast-feeding, and infants and young children. The elderly, who may not be eating a varied diet, may also be at risk. Strict vegetarians, vegans, and others on restricted diets may not receive adequate amounts of all vitamins.
In addition, people who suffer from disorders in which absorption of nutrients from the bowel is impaired, or who need to take drugs that reduce the absorption of vitamins (for example, some types of lipid-lowering drugs), are usually given additional vitamins. In these cases, the doctor is likely to advise supplements of one or more vitamins. Although most preparations are available without prescription, it is important to seek specialist advice before starting a course of vitamin supplements to obtain a proper assessment of your individual requirements.
Vitamin supplements should not be used as a general tonic to improve wellbeing (they are not effective for this purpose) nor should they be used as a substitute for a balanced diet.
Treating deficiency It is rare for a diet to completely lack a particular vitamin. But if intake of a particular vitamin is regularly lower than requirements, over time the body’s stores of vitamins may become depleted and symptoms of deficiency may appear. In Britain, vitamin deficiency disorders are most common among homeless people, alcoholics, and those on low incomes who fail to eat an adequate diet. Deficiencies of water-soluble vitamins are more likely since most are not stored in large quantities in the body.
Dosages of vitamins prescribed to treat vitamin deficiency are likely to be larger than those used to prevent deficiency. Medical supervision is required when correcting vitamin deficiency.
Other medical uses of vitamins Various claims have been made for the value of vitamins in the treatment of disorders other than vitamin deficiency. High doses of vitamin C have been said to be effective in preventing and treating the common cold, but such claims are not yet proved; zinc, however, may be helpful for this purpose. Vitamin and mineral supplements do not improve IQ in well-nourished children, but quite small dietary deficiencies can cause poor academic performance.
Certain vitamins have recognized medical uses apart from their nutritional role. Vitamin D has been used to treat bone-wasting disorders. Niacin is sometimes used (in the form of nicotinic acid) as a lipid-lowering drug. Derivatives of vitamin A (retinoids) are part of the treatment for severe acne. Many women who suffer from premenstrual syndrome take pyridoxine (vitamin B6) to relieve symptoms.
MAIN FOOD SOURCES OF VITAMINS
The table here indicates which foods are especially good sources of particular vitamins. Ensuring that you regularly select foods from a variety of categories helps to maintain adequate intake for most people, without the need for supplements. Processed and overcooked foods are likely to contain fewer vitamins than fresh, raw, or lightly cooked foods.
Normal daily vitamin requirements are usually given as recommended daily allowances or intakes (RDAs or RDIs). These are based on how much of a nutrient is enough, or more than enough, for 97 per cent of people. The RDA may vary with age, sex, and whether a woman is pregnant or breast-feeding. Deficiency usually needs much higher doses, which should be determined by your doctor.
Biotin No RDA established; 10–200mcg is considered safe.
Folic acid (as folate) 50mcg (birth–1 year); 70mcg (1–3 years); 100mcg (4–6 years); 150mcg (7–10 years); 200mcg (11 years and over). For a woman planning a pregnancy who is at low risk of having a baby with a neural tube defect, 400mcg per day before conception and during the first 12 weeks of pregnancy. A woman is considered to be at high risk if she or her partner has a personal or family history of neural tube defect; or if the woman has a malabsorption disorder, diabetes, sickle cell disease, or is taking anti-epileptic medication. A woman at high risk should take 5mg per day before conception and during the first 12 weeks of pregnancy; if she has sickle cell disease, she should continue taking 5mg per day throughout pregnancy. Daily requirements increase by 60mcg during breast-feeding.
Niacin 3mg (birth–6 months); 4mg (7–9 months); 5mg (10–12 months); 8mg (1–3 years); 11mg (4–6 years); 12mg (7–10 years and females 11–14 years); 15mg (males 11–14 years); 18mg (males 15–18 years); 14mg (females 15–18 years); 17mg (males 19–50 years); 13mg (females 19–50 years); 16mg (males 51 years and over); 12mg (females 51 years and over); 2mg extra during breast-feeding.
Pantothenic acid No RDA established; adults require 3–7mg daily.
Pyridoxine 0.2mg (birth–6 months); 0.3mg (7–9 months); 0.4mg (10 months–1 year); 0.7mg (1–3 years); 0.9mg (4–6 years); 1mg (7–10 years and females 11–14 years); 1.2mg (males 11–14 years); 1.5mg (males 15–18 years); 1.2mg (females 15 and over); 1.4mg (males 19 and over).
Riboflavin 0.4mg (birth–1 year); 0.6mg (1–3 years); 0.8mg (4–6 years); 1mg (7–10 years); 1.2mg (males 11–14 years); 1.1mg (females 11 and over); 1.3mg (males 15 and over); extra 0.3mg in pregnancy and 0.5mg during breast-feeding.
Thiamine 0.2mg (birth–9 months); 0.3mg (10–12 months); 0.5mg (1–3 years); 0.7mg (4–10 years and females 11–14 years); 0.9mg (males 11–14 years); 1.1mg (males 15–18 years); 0.8mg (females 15 and over); 1mg (males 19–50 years); 0.9mg (males 51 and over). Extra 0.1mg in last three months of pregnancy and 0.2mg during breast-feeding.
Vitamin A 350mcg (up to 1 year); 400mcg (1–6 years); 500mcg (7–10 years); 600mcg (males 11–14 years, females 11 years and over); 700mcg (males 15 and over, and pregnant women); 950mcg (breast-feeding).
Vitamin B12 Only minute quantities required. 0.3mcg (birth–6 months); 0.4 mcg (7–12 months); 0.5mcg (1–3 years); 0.8mcg (4–6 years); 1mcg (7–10 years); 1.2mcg (11–14 years); 1.5mcg (15 years and over); extra 0.5mcg per day during breast-feeding.
Vitamin C 25mg (birth–1 year); 30mg (1–10 years); 35mg (11–14 years); 40mg (15 years and over); 50mg in pregnancy; 70mg during breast-feeding.
Vitamin D 8.5mcg (birth–6 months); 7mcg (7 months–3 years); 10mcg (over 65 years, pregnancy, and breast-feeding). Most people outside these groups do not require supplements.
Vitamin E No official UK RDA. Requirement depends on intake of polyunsaturated fatty acid, which varies widely; (approximate recommended requirement 3–15mg per day.
Vitamin K Newborn infants may be given 1mg by single injection or they may receive the vitamin orally; 2 doses of 2mg are given in the first week and a third dose at 1 month for breast-fed babies (omitted in formula-fed babies). No RDA has been set for other groups.
RISKS AND SPECIAL PRECAUTIONS
Vitamins are essential for health, and supplements can be taken without risk by most people. It is important not to exceed the recommended dosage, particularly for fat-soluble vitamins, which may accumulate in the body. Dosage needs to be carefully calculated, taking into account the degree of deficiency, dietary intake, and duration of treatment. Overdosage has no therapeutic value and may even be harmful. Multivitamin preparations do not usually contain large amounts of each vitamin and are not likely to be harmful unless the dose is greatly exceeded. Single vitamin supplements can be harmful (excess of one vitamin may increase requirements for others) and should be used only on medical advice.
Minerals are chemical elements (the simplest form of substance), many of which are vital in trace amounts for normal body processes. A balanced diet usually contains all the minerals needed; mineral deficiency diseases, except iron-deficiency anaemia, are uncommon.
Dietary supplements are necessary only when a doctor has diagnosed a specific deficiency, or as part of the prevention or treatment of a disorder. Doctors often prescribe minerals for people with intestinal diseases that reduce absorption of minerals from the diet. Iron supplements are often advised for pregnant or breast-feeding women, and iron-rich foods for infants over six months.
Taking mineral supplements unless under medical direction is not advisable. Exceeding the body’s daily requirements is not beneficial, and large doses may be harmful.
As with vitamins, normal daily mineral requirements are usually based on the recommended daily allowance (RDA).
Calcium 525mg (birth–1 year); 350mg (1–3 years); 450mg (4–6 years); 550mg (7–10 years); 1,000mg (males 11–18 years); 800mg (females 11–18 years); 700mg (19 years and older); 550mg extra during breast-feeding.
Chromium Only minute quantities needed. RDA not established; about 25mcg is considered safe for adults.
Copper 0.2mg (birth–3 months); 0.3mg (4 months–1 year); 0.4mg (1–3 years); 0.6mg (4–6 years); 0.7mg (7–10 years); 0.8mg (11–14 years); 1.0mg (15–18 years); 1.2mg (19 years and over); 0.3mg extra during breast-feeding.
Fluoride No RDA established.
Iodine 50mcg (birth–3 months); 60mcg (4–12 months); 70mcg (1–3 years); 100mcg (4–6 years); 110mcg (7–10 years); 130mcg (11–14 years); 140mcg (15 years and over). Slightly increased requirement during breast-feeding: one vitamin tablet with calcium and iodine is recommended.
Iron 1.7mg (birth–3 months); 4.3mg (4–6 months); 7.8mg (7–12 months); 6.9mg (1–3 years); 6.1mg (4–6 years); 8.7mg (7–10 years); 11.3mg (males 11–18 years); 14.8mg (females 11–50 years); 8.7mg (males 19 and over, and females 51 and over). Requirements may be increased during pregnancy and after childbirth.
Magnesium 55mg (birth–3 months); 60mg (4–6 months); 75mg (7–9 months); 80mg (10–12 months); 85mg (1–3 years); 120mg (4–6 years); 200mg (7–10 years); 280mg (11–14 years); 300mg (males 15 and over, and females 15–18 years); 270mg (females 19 and over); 50mg extra during breast-feeding.
Potassium 0.8g (birth–3 months); 0.85g (4–6 months); 0.7g (7–12 months); 0.8g (1–3 years); 1.1g (4–6 years); 2g (7–10 years); 3.1g (11–14 years); 3.5g (15 years and over).
Selenium 10mcg (birth–3 months); 13mcg (4–6 months); 10mcg (7–12 months); 15mcg (1–3 years); 20mcg (4–6 years); 30mcg (7–10 years); 45mcg (11–14 years); 70mcg (males 15–18 years); 60mcg (females 15 and over); 75mcg (males 19 and over); 15mcg extra during breast-feeding.
Sodium 0.21g (birth–3 months); 0.28g (4–6 months); 0.32g (7–9 months); 0.35g (10–12 months); 0.5g (1–3 years); 0.7g (4–6 years); 1.2g (7–10 years); 1.6g (11–18 years); 1.9g (females 19 and over); 2.3g (males 19 and over). (1 teaspoon – 6g – of table salt contains about 2g of sodium.)
Zinc 4mg (birth–6 months); 5mg (7 months–3 years); 6.5mg (4–6 years); 7mg (7–10 years); 9mg (11–14 years); 9.5mg (males 15 years and over); 7mg (females 15 years and over); 13mg during first 4 months of breast-feeding and 9.5mg thereafter.
MAIN FOOD SOURCES OF MINERALS
The table here indicates foods that are especially good sources of particular minerals. A balanced diet usually contains all the minerals required by the body without the need for supplements. Some, known as trace elements, are required only in minute amounts.