Minerals
Iva Řehová
What are minerals?
• Minerals are nutrients that are needed in the
body in tiny amounts.
• The amount of each mineral we need changes
during our lifetime.
Minerals are inorganic substances required by
the body for a variety of functions including:
They form the architecture of bones,
• they are constituents of body fluids,
• they help enzymes to work,
• they help nerves to send signals.
• Some minerals are needed in larger amounts
than others, e.g. calcium, phosphorus,
magnesium, sodium, potassium and chloride.
• Others are required in smaller quantities and are
sometimes called trace minerals, e.g. iron,
zinc, iodine, fluoride, selenium and copper.
Despite being required in smaller amounts, trace
minerals are no less important than other
minerals.
• Different foods supply different amounts of
minerals.
• Eating a varied diet will help ensure an adequate
supply of most minerals for healthy people.
• In westernized societies, iron and calcium
intakes are gradually decreasing.
• A minority of the population has low intakes of
a number of minerals e.g. potassium,
magnesium and zinc. This is particularly the
case among teenagers, young adults and older
adults.
Calcium
function:
• Calcium is the main constituent of hydroxyapatite, the principal mineral
in bones and teeth.
• Calcium also plays an essential role in intracellular signalling and is
therefore necessary for nerve and muscle function.
• It is also involved in blood clotting.
• The absorption and excretion of calcium are controlled by several
hormones and by vitamin D.
deficiency:
• In children, vitamin D deficiency results in rickets and in adults
osteomalacia, in which bones become weak owing to lack of calcium.
• A significant proportion of young women have average calcium intakes
below RDA (8% of women aged 19-24 years and 6% of women aged
25-34 years.
• An adequate calcium intake is vital for health, particularly in times of
growth, e.g. childhood, adolescence, pregnancy, and also during
lactation (breastfeeding).
• Peak bone mass is reached by the age of about 30
years, with 90-95% reached by 20 years.
• After this age, some loss of calcium from bone is normal
and bone mass slowly decreases.
• However, severe loss causes the bones to become
weak, brittle and to break easily. This condition is known
as osteoporosis.
• Osteoporosis occurs if large amounts of bone (not just
calcium) are lost, or if the bones are not strong before
bone loss begins. It most frequently affects older
women who have gone through the menopause
(oestrogen has a protective effect on bone), although
men can also be affected. Currently, it is believed that 1
in 3 women and 1 in 8 men aged over 50 will suffer
some degree of osteoporosis during their life.
• sources: Foods that are particularly rich in calcium are
milk, cheese and other dairy products (but not butter).
White and brown flour, so bread and other products
made from this are important sources of calcium.
• Calcium is most readily absorbed from milk and
dairy products (particularly from acidified products).
• It is often less available from plant foods where the
calcium may be bound by phytates (found in wholegrain
cereals and pulses) and oxalates (found in spinach and
rhubarb) in foods, which makes the calcium unavailable
for absorption from the intestine into the blood.
• However, absorption from some plant foods is good e.g.
broccoli, although the amount present may be lower than
in milk.
• supplementation: There is some evidence that
calcium supplementation may have a small
benefit in women after the menopause,
although other factors, including weight and
hormonal status are more important.
• In older women, the evidence for benefits of
supplementation with calcium and vitamin D is
stronger, and an adequate intake of calcium
and vitamin D, combined with physical activity,
seems to reduce fracture risk.
• Adequate calcium intake may also be important
in other disease processes - in the prevention
of high blood pressure, obesity and bowel
cancer.
Magnesium
function:
• Magnesium is present in all tissues including bone.
• It is required for normal energy metabolism and electrolyte balance.
• It is also needed for muscle function and for bone and tooth
structure.
sources:
• It is present in all foods but as magnesium is found in chlorophyll, the
green pigment in plants, it is abundant in dark green leafy vegetables,
but much of it is bound and not readily available for absorption.
• Grains and nuts are also rich in magnesium, providing about a quarter
of total intake among adults.
deficiency:
• Although strong deficiency is rare, low intakes have been observed in
some groups, e.g. one in five women aged 19-34 years.
• Teenagers are also at risk of low intakes with just over half of teenage
girls having intakes below the RDA (51% of 11-14 age group and 53%
of 15-18 age group) and more than 20% of boys aged 11-14 years are
at risk of low intakes.
Phosphorus
function:
• It is essential for bone and tooth structure,
• for the structure of cell membranes (in phospholipids)
• and for energy metabolism.
sources:
• Phosphorus is present in all plant and animal cells.
Milk, cheese, meat, fish and eggs are good sources
deficiency:
• It is found in many foods and is unlikely to be in short
supply in diets.
Sodium
function:
• Sodium helps regulate body water content and electrolyte balance,
• and is involved in energy utilisation and nerve function.
• It is also required for the absorption of certain nutrients and water from the
gut.
sources:
• Salt
• The average intake of salt in the UK is 11.0 g/day for adult men and 8.1 g/day
for adult women, compared with the recommendation of 6 g per day in adults
deficiency:
• Fatigue, nausea, cramps. Excess sweating, e.g. due to exercise in a hot
environment, may cause some sodium depletion.
excess intake:
• Too much salt in the diet is associated with an increased risk of raised blood
pressure, which is a risk factor for heart disease and stroke. A low salt diet
may be used in the treatment of hypertension.
Potassium
function:
• Potassium is found in body fluids and is essential for water and
electrolyte balance
• and for the proper functioning of cells, including nerves.
sources:
• It is present in almost all foods but fruit (e.g. dried fruits, bananas, berry
fruits), vegetables and milk are rich sources.
• Processed foods typically contain less than raw foods.
deficiency:
• Weakness, mental confusion and, if extreme, heart failure.
• Low dietary potassium intakes have been observed about 1 in 5 women.
• In the RDA of young people, 10–15% of boys had intakes below the RDA
but among girls, about 1 in 5 11-14 year olds and about 2 in 5 15–18 year
olds had intakes below the RDA.
• Potassium has a beneficial blood pressure-lowering effect in people with
raised blood pressure.
Iron
function:
• Iron is required for the formation of haemoglobin in red blood cells, which transport
oxygen around the body.
• Iron is also required for normal energy metabolism,
• and for metabolism of drugs and foreign substances that need to be removed from the
body.
• The immune system also requires iron for normal function.
sources:
• Iron is found in animal and plant sources.
• Red meat, cereals, bread, and vegetables are rich sources.
• Iron from animal sources (haem iron) is better absorbed than iron from plant sources (nonhaem iron).
• Absorption of non-haem iron is affected by various factors in food. Phytate (in cereals
and pulses), fibre, tannins (in tea) and calcium can all bind non-haem iron in the
intestine, which reduces absorption.
• On the other hand vitamin C, present in fruit and vegetables, aids the absorption of this
kind of iron when eaten at the same time. The same applies to meat, fish and poultry.
deficiency:
• A lack of iron leads to low iron stores in the body and eventually to iron deficiency
anaemia.
• Loss of blood due to injury or large menstrual losses increases iron requirements.
• Women of child bearing age and teenage girls, in particular, need to ensure their diet
supplies enough iron as their requirements are higher than those of men of the same age.
• Average daily iron intakes from foods are below the RDA for women in all age groups,
except for older women (over the age of 54 years).
Trace Elements
Zinc
function:
• antioxidant
• Zinc is present in many enzymes and is essential for cell division and,
therefore, for growth and tissue repair.
• It is also necessary for normal reproductive development.
• Zinc is also required for the functioning of the immune system and in
the structure and function of the skin
• and, therefore, in wound healing.
sources:
• Zinc is present in many foods and is most readily absorbed from
meat,
• Milk, cheese, eggs and fish, wholegrain cereals and pulses are rich
sources.
• For cereals and pulses, zinc’s availability is limited by phytates.
deficiency:
• Dietary deficiency is rare.
Iodine
function:
• Iodine is used to make thyroid hormones. The thyroid hormones control
many metabolic processes and if there is insufficient iodine in the diet, the
result is lethargy and swelling of the thyroid gland in the neck to form a
goitre.
• Iodine is also required for normal neurological development and for
energy metabolism.
• Infants born of severely iodine deficient mothers may be mentally retarded
(cretinism).
sources:
• The amount of iodine in plant foods such as vegetables and cereal grains
is determined by the iodine level of the environment, i.e. the amount in the
soil or water.
• The only rich sources of iodine are sea-foods, but in some countries certain
foods, e.g. salt and bread, are fortified with iodine. In Europe, dairy
products are an important source of iodine.
deficiency:
•
Nowadays iodine deficiency is very rare in Europe.
Fluoride
function:
• It contributes to the maintenance of bone health by
supporting bone mineralisation and it protects teeth
against dental decay (caries).
sources:
• Fluoride is found in few foods (fish, tea) but in varying
quantities in water.
• The addition of fluoride to toothpaste is now very
common and is important in those areas where the water
supply is low in fluoride.
deficiency:
• tooth decay
excess intake:
• mottling of teeth, and changes to the bones - a condition
called fluorosis.
Selenium
function:
• antioxidant
• It is also necessary for the use of iodine in thyroid
hormone production
• and for immune system function.
sources:
• Sources of selenium include cereals, fish, eggs and
brazil nuts.
deficiency:
• Selenium deficiency has been linked with a form of heart
disease (Keshan disease) in parts of China where soil
levels of selenium are very low.
Copper
function:
• Copper is a constituent of many enzyme systems
• and the body needs copper to be able to use iron
properly.
• It is needed for the structure of connective tissue in
bone, the lungs and blood vessels.
sources:
• Good sources of copper include green vegetables, fish,
liver, nuts, cereals and cereal products.
deficiency:
• Dietary deficiency is extremely rare but copper
deficiency may arise because of a genetic defect
(Menke’s syndrome).
Chromium
function:
• It has been suggested that it may be involved in
the action of insulin, the hormone which
controls glucose levels in the blood. However,
there is still no general agreement for the role of
chromium in insulin metabolism.
sources:
• Chromium is found in a variety of foods – meat,
liver, egg yolk, sea foods, cheese, cereals
deficiency:
• impaired glucose tolerance
Manganese
function:
• antioxidant
• Manganese is required for bone formation and for energy metabolism.
sources:
• It is present in plant foods such as vegetables, cereals and nuts. Tea is also
a rich source.
deficiency:
• Dietary deficiency is rare.
Other trace elements
•
•
There are other minerals which are needed in tiny amounts and which
appear to be essential in the diet, e.g. molybdenum, boron.
Others occur in the diet, but whether they are essential is unclear, e.g.
nickel, lithium, antimony, aluminium and lead.
The bioavailability and
absorption of minerals
The bioavailability of a mineral (i.e. how readily it can be
absorbed and used by the body) may be influenced by a
variety of factors:
• Phytate and oxalate, found in some foods, reduce the
absorption of calcium, iron and zinc.
• Iodine absorption may be blocked by nitrates.
• An excess of one mineral may blocked the absorption of
another, e.g. excess iron reduces zinc absorption.
• In contrast, iron absorption may be increased when
vitamin C is consumed during the same meal.
Minerals and diseases
• Iron deficiency anaemia is a common problem, often affecting
women and young children throughout the world.
• Deficiencies of other minerals are rare in the westernized societies
and excess intakes are sometimes a concern (e.g. sodium).
• Research has suggested that selenium, manganese and zinc may
form part of the body's defences against free-radicals (substances
produced naturally by the body or present in cigarette smoke, which
have been linked to various chronic diseases).
• There is some research into the role of these minerals (and also some
vitamins) in helping to protect against common diseases, such as
some types of cancer and heart disease.
• Although inclusion of these nutrients in the diet seems to be
important, a role for supplements has not been clearly
demonstrated.
• Supplements (especially if taken in an unsupervised manner) may
cause mineral imbalances or have other side-effects; some
minerals are toxic when taken in excess.