Nutrition
Minerals
Did you know?
Iron from chicken and meat is easier for our bodies to use than iron from vegetables.
News in a hurry
- Minerals can affect the absorption of each other – this has implications when taking supplements.
- Minerals are less likely than vitamins to be lost through cooking.
- Many Kiwis are not getting enough iodine in their diets.
- Fortification of stock food in New Zealand and eating imported foods, like Aussie wheat and Brazil nuts, help maintain healthy selenium levels.
- Coffee, tea and bran all decrease iron absorption – so have them between meals.
- For healthy bones, eat calcium rich foods, cut salt and alcohol intake, remain smoke free and exercise regularly.
- Many Kiwis eat more than recommended daily upper limit of sodium, which comes from salt included in many processed foods and some drinks. Read food labels, choose low sodium products, reduce salt in cooking and avoid snacking on salty foods. Try not to add salt at the table.
- The 2003 New Zealand Food and Nutrition Guideline statement refers to the ‘four food groups’: read more about each of them in our pages on fruit and vegetables, breads and cereals, milk and milk products, lean meat and meat alternatives, and how to make them part of a balanced diet.
What are minerals?
Minerals are inorganic compounds essential to all living things. They are found in the soil and hence end up in our food supply. If a country’s soil is poor in a certain mineral, there may be the need to fortify animal feed or certain foods.
Bone minerals
Calcium and phosphate, both are needed in relatively large amounts. Calcium is also needed in large amounts for muscular activity. Fluoride, although not essential, helps prevent tooth decay by forming a compound which stabilizes the mineral matrix in teeth.
Electrolytes
Sodium, chloride, potassium and magnesium, all highly soluble and needed for such things as controlling water balance, muscle contraction and conducting nerve impulses.
Trace elements
Iron, iodine, selenium, chromium, manganese, molybdenum and copper, are essential and needed in very small amounts. Except for chromium, each of these is incorporated into enzymes or hormones required in metabolism.
Trace mineral deficiencies are uncommon in developed countries, with the exception of deficiencies of iron and zinc. However, in New Zealand selenium and iodine soil levels are low, so precautions need to be taken. All trace minerals are toxic at high levels, and some (arsenic, nickel, and chromium) may cause cancer.
Minerals of dietary importance to New Zealanders
| Iron |
| Role |
Important for haemoglobin that carries oxygen in blood, and myoglobin that carries oxygen in muscles. Also present in many enzymes that help to release energy from food. Iron needs are greatest in women of child bearing age, and is especially important for infants during fast brain development. |
| Sources |
Liver, meats, poultry and shellfish like mussels, oysters and canned shrimp. Also egg yolk, whole grains, enriched bread and cereal, dark green vegetables, legumes and nuts – but is less available to the body when obtained from these foods. Foods rich in vitamin C increase iron absorption, while foods that decrease absorption include bran, tea, coffee – these foods should be taken between meals. Most New Zealanders get an adequate amount of iron in their diets. When iron stores are low more will be absorbed from food. |
| Decificiency |
Can cause tiredness, fatigue, feeling run down and susceptibility to infection and can lead to anaemia. In New Zealand, iron deficiency mainly affects females 15-44 years of age, with the highest rates in Maori females; men are not generally iron deficient. The iron status of women in New Zealand appears to be slightly better than that of women in other western countries, despite lower or similar iron intakes. Iron intakes in female vegetarians are slightly higher than that of non-vegetarians.See our dietitian's article about getting enough iron and iron deficiency. |
| Toxicity |
Can damage organs and lead to greater susceptibility to infections. People with an inherited condition called haemochromatosis can retain too much iron, as can those with another inherited disorder, thalassaemia. Special note: Iron supplements should be taken only under medical supervision.
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| RDI/AI/UL |
RDI: Male, 19-70 plus years, 8mg. Females 19-50 years, 18mg; 51 plus years 8mg. |
| Iodine |
| Role |
A component of thyroid hormone, needed for growth and development, as well as mental function. |
| Sources |
Iodised salt, seafood and seaweed products. When you do add salt to your food, make sure it’s iodised, and try to eat seafood regularly.
Special note: Kelp and iodine supplements should only be taken under supervision of a doctor or dietician.
When eaten in very large quantities, veges like cabbage, broccoli and Brussels’ sprouts can interfere with the production of thyroid hormones, and sweet potato and maize can interfere with the uptake of iodine by the thyroid gland. Losses of iodine can occur in cooking.
|
| Deficiency |
Results in a range of conditions collectively called iodine deficiency disorders. In severe deficiency, these include foetal abortion or stillbirth, congenital anomalies, increased peri natal and infant mortality, neurological cretinism or mental deficiency with deaf mutism, spastic diplegia and squint, cretinism and dwarfism and psychomotor effects. This is not seen in New Zealand. More importantly for us, low iodine levels in children may cause learning difficulties, and there is some evidence that this is a problem in New Zealand.
All throughout life, iodine deficiency can lead to goitre or hypothyroidism as well as impaired mental and physical development. With reduced thyroid hormone production, the thyroid gland enlarges to increase its output. The swollen gland in the neck is called a goitre. |
| New Zealand levels are dropping |
The iodine content of most foods is low and can be affected by soil, irrigation and fertilisers. Most soils in New Zealand are low in iodine – with the major food sources coming from the sea. In the 1920s and 30s, New Zealand experienced endemic mild to moderate iodine deficiency – goitre became a common sight. In 1938, iodine was added to a then commonly used food – table salt. This helped to eradicate goitre in the 1950s. Iodophores used by the dairy industry, which resulted in putting iodine into the food supply, were major contributors to iodine intake in Australia and New Zealand in the 1960s. However, this practice was changed in the early 1970s leading to reduced iodine in milk. Nowadays we tend not to use so much salt in our food, we eat out more, consuming non-iodised salt when we do. All this means we are lowering our iodine consumption in both countries, and large studies are showing mild deficiency in adults, breast feeding mothers and children alike. |
| RDI/AI/UL |
RDI: 150µg men and women.
|
| Selenium |
| Role |
The control of thyroid hormone metabolism, reproduction, immunity and it works with vitamin A as an antioxidant. Low selenium levels are evident in smokers. And, although there have been suggestions that low levels are linked to cardiovascular disease and cancer, there is no conclusive evidence that selenium protects against these. |
| Sources |
Fish and seafood, poultry, meat and eggs. What we gain from cereals and plant foods depends on where they were grown, eg, brazil nuts are high in selenium because soil in that part of the world has higher levels of this mineral. By eating homegrown meats and poultry and a range of imported plant foods, like brazil nuts and Australian wheat, the intake of selenium is at or around recommended levels, according to the 1997 National Nutrition Survey and the 1997/98 New Zealand Total Diet Survey.
Special note: Selenium supplements are not recommended unless supervised by a doctor.
|
| Deficiency |
New Zealand soil is deficient in this trace element, and several interventions have been introduced to ensure the food supply has adequate amounts to prevent deficiency, eg, animal feed is supplemented with selenium. |
| RDI/AI/UL |
RDI: Men 70µg. Women 60µg. |
| Zinc |
| Role |
Involved in a number of major processes, including making protein, and is essential for making insulin. It is a component of enzymes, skin and important for wound healing. |
| Sources |
Zinc is widely available from the food supply, but zinc from animal products, crustacean and mollusks is more readily absorbed than zinc from plant foods. Rich sources: oysters, red meat, lamb’s liver and cheese. But cereal grains, legumes and nuts are rich in phytates, which reduce zinc absorption. The best sources for vegetarians are almonds and peanuts, lima beans, unrefined cereals and low–fat milk and milk products. Vegetarians, particularly strict vegetarians whose main foods are grains and legumes, may need as much as 50% more dietary zinc than non-vegetarians. |
| Deficiency |
Is not very common: less than 2% of New Zealanders are at risk, with women in the most deprived areas at highest risk. Symptoms include tiredness, a decreased appetite and ability to taste food, and impaired immunity. Decreased absorption can be due to a high intake of a substance called phytate (found in nuts, cereals and legumes), alcoholism, excessive diarrhoea and vomiting and increased requirements during growth, pregnancy and breast feeding. Eating a lot of calcium-rich foods together with foods rich in phytate, further decrease zinc absorption, putting vegetarians at particular risk. High intakes of iron supplements can also reduce zinc absorption.
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| Toxicity |
Too much zinc results in a metallic taste in the mouth, nausea, fever, lethargy and gastric upsets. This can occur after taking supplements or exposure to zinc in the environment. Very large doses can be fatal. Long term consumption of moderately high amounts of zinc, changes the concentration of fats, which can increase the risk of coronary heart disease. |
| RDI/AI/UL |
RDI: Men 14mg. Women 8mg. |
| Calcium |
| Role |
Essential for bone formation throughout life, for and muscle and nerve activity (including healthy heart function). Also plays a role in blood clotting and cell division. For this reason the amount we need is relatively large compared with other minerals. When we don’t get enough calcium in our diet, our bodies take it from our bones, which leads to osteoporosis and results in broken bones.
Many things affect the balance of calcium: it’s lost through the gut, urine and skin, and this activity is increased by foods that contain sodium, protein and caffeine; we need vitamin D to absorb calcium, but some nutrients, like fibre and phytates, tend to decrease absorption; and while regular physical activity is good for the deposit of calcium in our bones, excessive activity combined with an inadequate diet, is not. |
| Sources |
Best sources are dairy foods: milk, cheese, yoghurt, but also get it from fortified soy drinks and breakfast cereals, nuts, canned fish with bones, leafy vegetables, broccoli, peas, beans and lentils, dried fruits and whole meal bread. Lacto-ovo-vegetarians appear to have similar calcium intakes to omnivores.
Special note: Care is needed taking supplements, as too much calcium over time can be harmful to your kidneys and heart*
|
| Deficiency |
Quite common in New Zealand, with 1 in 5 not getting enough. A greater number of women are deficient than men, while low levels are more common among Maori than non-Maori. We maintain our blood levels of calcium by taking it from our bones. A deficiency in children will stunt growth and result in poor quality teeth and bones and an increased risk of fractures. Adults will experience aches and pains, lose height and develop brittle bones.
Bone mass increases by about 7 fold from birth to puberty, a further 3 fold during
adolescence, then remains stable until about age 50 in men and until the menopause
in women. Peak bone mass is, therefore, achieved in teenage years, so it is especially important at this time to get the recommended daily intake of calcium.
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| * Women and calcium |
At menopause women will experience a decline in calcium absorption and/or an increase in calcium excretion – putting them at increased risk of osteoporosis and bone fracture. The Nutritional Reference Values for Australia and New Zealand 1997 says in post menopausal women, a high calcium intake will slow the rate of bone loss and may reduce the risk of fracture.
However, it is not proven that getting your calcium from supplements will have this effect, and recent studies have begun to show there may be an upward trend in heart attacks and other cardiovascular problems in postmenopausal women taking calcium supplements. We need calcium for healthy bones and teeth, but it may be safest to get yours from what you eat and drink, rather than from taking a supplement. New Zealand osteoporosis researcher Professor Ian Reid advises against calcium supplementation in people over the age of 70 years and in those known to have coronary heart disease. In younger people who may be wishing to avoid osteoporosis, he says it may be sensible to aim for a smaller dose, say 500mg/day. |
| RDI/AI/UL |
RDI: Male and female: 1000mg for 9 to 11-year-olds and 1300mg for 12 to 18-year-olds. |
| Sodium |
| Role |
An electrolyte needed both inside and outside of cells for fluid balance, energy transfer and the uptake of nutrients. Very small amounts of sodium are needed and most people eat far too much of it. |
| Source |
In soil, sodium is bound to other chemicals, and is most commonly found in many of our foods. It's present as sodium chloride (90% of our sodium intake), sodium bicarbonate and monosodium glutamate in processed foods. It’s also present in other food additives such as sodium phosphate, sodium carbonate and sodium benzoate. |
| Deficiency |
Sodium levels can fall after excessive exercise or sweating and lead to muscle cramps. Sodium can also be reduced through prolonged bouts of vomiting and diarrhea – an electrolyte replacement drink may help correct this.
|
| Toxicity |
Deficiency is not as much a problem as sodium excess. High intakes of sodium are linked to high blood pressure, a risk factor for developing kidney and cardiovascular disease, especially stroke. Reducing salt is an important goal and is now thought to be more important in its effects on reducing the risk of heart attacks and strokes than stopping smoking (but you should do both!). If you are older, overweight or have high blood pressure, diabetes or chronic kidney disease you are more likely to be sensitive to the blood pressure raising effects of salt. If others in your family have raised blood pressure in response to higher levels of sodium chloride, you may be more likely to as well. Diets high in potassium can help counteract this. This is best achieved by eating more fruits and vegetables. In people who do not have raised blood pressure, reduced sodium intake can decrease the risk of developing hypertension. A 2007 World Cancer Research Fund study found both salt and foods preserved with salt are probably associated with an increased risk of stomach cancer.
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| RDI/AI/YL |
AI: 20-40 mmol/day
UL: 100 mmol/day
Not enough is known about estimated average requirements for sodium, so an RDI cannot be calculated.
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| How much do we consume? |
Estimated intakes in New Zealand are about 150 mmol/day – more than we need and above the recommended upper limit. The amount the body needs each day is far less than what we are eating! You may think you are regulating your salt intake by reducing its inclusion in cooking and at the table, but many foods contain ‘hidden’ salt. Up to 85% of our sodium comes from eating processed or manufactured foods. For this reason, we are eating more salt than we perhaps realize and putting our health at risk. A WASH study has found many New Zealand take-aways and processed foods, like burgers, fish and chips and even cornflakes, have more salt in them that their Australian and UK equivalents.
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Reduce sodium intake, reduce blood pressure
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To achieve the level of sodium intake required to have an impact on blood pressure (<100mmol/day), you need to do much more than just avoiding adding salt to your food. It requires other measures such as:
- Cooking from scratch and don’t add sachets.
- Look for foods that contain <150mg sodium per serve. (Write this down and pop it in your wallet to retrieve when you are grocery shopping).
- Using herbs and low sodium spices to flavour food.
- Increase potassium by eating fruit and vegetables.
- Reduce intake by avoiding salty foods, reading food labels and choosing low sodium products and preparing meals with minimal salt – remember to make it iodised!
- To be labeled ‘low sodium’, foods need to be,120mg/100g.
- Limit intake of sausages and salamis.
- Reduce intake of dehydrated foods, such as seasoning mixes and soups.
- Choose fish canned in spring water.
- Make bread at home in a bread machine.
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| Know your food labels |
Salt is listed in the ingredients list, sodium in the nutrition panel.
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Read RDIs explained