The facts about vitamins and minerals
We all know we need vitamins and minerals in our diets. But why are they so important for good health? How much do we need and can we get enough from food? Fionna Carruthers uncovers the facts.
If we think of fat, protein and carbohydrates as the building blocks of our food, vitamins and minerals are the nuts and bolts. They work together with each other, as well as enhancing the effectiveness of the building blocks. Imagine building a car. Without the nuts and bolts, it would be little more than a pile of metal panels.
‘Vita’ means life, and it has been known since 1500BC that specific nutrients can treat disease. In the 18th century, a Scottish naval surgeon discovered the curative effect of citrus fruit on his sailors’ scurvy. Hence the British being called ‘Limeys’, named after the limes used to treat scurvy at sea. It was not until the early 1900s that this was attributed specifically to vitamin C.
Similarly, vitamin B1 was discovered at this time through the restorative effect of unpolished rice, a rich source of vitamin B1, on sufferers of beriberi, a wasting disease. Vitamin D was then found to cure rickets, a bone deformity disease, and so it went on until the 1930s when all thirteen of today’s vitamins had been identified.
Two types of vitamins
Vitamins are divided into two types: water-soluble and fat-soluble. Neither is more important than the other, but they are very different in terms of what they do and where they are found.
The majority of vitamins are water-soluble, namely all the B vitamins and vitamin C. Because water-soluble vitamins are dissolved in our body fluids, we are unable to store these vitamins, making a regular supply essential to our well-being. In contrast, fat-soluble vitamins A, D, E and K can be stored in the body’s fat deposits, in which they are both transported and stored.
Most vitamins have two names, eg. vitamin C is also known as ascorbic acid. Apart from vitamin D, which we can make from the action of sunlight on our skin, and some of both B vitamin biotin and vitamin K, made by the beneficial bacteria in our gut, the rest must be found in our food.
Water-soluble vitamins and their function
- Vitamin B1 (Thiamin) – Releases energy from carbohydrates.
- Vitamin B2 (Riboflavin) – Releases energy from protein, fat and carbohydrate; promotes healthy skin and eyes.
- Niacin (Vitamin B3) – Releases energy from protein, fat and carbohydrate; involved in cholesterol production.
- Pantothenic Acid (Vitamin B5) – Releases energy from carbohydrate, fat and protein.
- Vitamin B6 (Pyridoxine) – Breaks down protein; helps to make red blood cells.
- Vitamin B12 (Cyanocobalamin) – Helps to make red blood cells, nerve cells and genetic material (DNA); breaks down carbohydrate and fat.
- Folate (Folic acid) – Helps to make red blood cells and enzymes and prevents neural tube defects; breaks down DNA material and reduces levels of homocysteine (high levels are a risk factor for cardiovascular disease).
- Biotin – Breaks down fat and protein Promotes growth and healthy nerve cells.
- Vitamin C (Ascorbic acid) – Forms collagen (an essential component of the skin, blood vessels, bone and teeth); acts as an antioxidant, providing resistance to infections and promoting wound healing; improves non-haem iron absorption.
Fat-soluble vitamins and their function
- Vitamin A* (Retinol) – Maintains healthy skin and eyes, improving vision at night and in dim light; acts as an antioxidant, having a role in cancer prevention.
- Vitamin D (Cholecalciferol) – Promotes strong bones and teeth.
- Vitamin E (Tocopherols) – Maintains healthy cell membranes; acts as an antioxidant.
- Vitamin K (Phylloquinone) – Needed for normal blood clotting.
* Vitamin A also occurs as beta-carotene in our food, being converted into retinol in the body.
Minerals: Little and large
Minerals form the body’s backbone – literally as well as metaphorically. Some, like calcium and fluorine, are structural, whereas others are essential to the many chemical and electrical reactions occurring every second of every day within the body. As a friend once said to me, “I feel like one big chemical experiment, diluted down with a bit of water.” Some minerals are needed in larger quantities than others, hence the term ‘trace minerals’ for those needed in minute amounts. We don’t need much of each trace mineral, but what we do need is essential.
Major minerals and their function
- Calcium – Forms the structure of bones and teeth; assists nerve function, muscle contraction, enzyme activity and blood clotting.
- Iron – Transports oxygen around the body via red blood cells; important part of many enzymes and muscle protein.
- Magnesium – Controls nerve signals and muscle contractions, and is involved in many enzyme systems; forms the structure of bones and teeth.
- Phosphorus – Works with calcium in forming the structure of bones and teeth; releases energy from carbohydrates, fats and protein; important part of many enzymes and DNA.
- Potassium – Maintains water and acid-base balance in the body and nerve impulses by working with sodium; involved with many enzyme systems.
- Sodium – Maintains water and acid-base balance in the body and nerve impulses by working with potassium.
Trace minerals and their function
- Chromium – Regulates blood glucose through its action on insulin.
- Copper – Produces colour pigments in skin, hair and eyes; promotes nervous system function and red blood cell formation.
- Fluoride – Strengthens teeth and bone; reduces tooth decay.
- Iodine – Necessary for thyroid function, needed for normal growth.
- Selenium – Acts as an antioxidant; promotes a healthy immune system and resistance to disease; necessary for adequate thyroid function
- Zinc – Promotes normal growth, wound healing and immune system function, reproduction and sensory abilities, such as taste, smell and sight.
How much is enough?
It is quite easy to visualise the ‘building blocks’ of our food. Fat we can see as a lump of butter; protein as a piece of meat; carbohydrate as a slice of bread. Vitamins and minerals aren’t so obvious because they’re invisible to the naked eye. So how much do we need? And how much is enough?
Earlier this year, the Ministry of Health along with the National Health and Medical Research Council of Australia published a set of tables detailing the amount of 28 vitamins and minerals we need to eat each day, based on the best available scientific evidence. You will see these amounts on food labels as the term %RDI, showing how much of the recommended amount a serving of that particular food provides. RDI stands for ‘recommended dietary intake’. These amounts are set according to age and many of them differ between men and women. They are deemed to be enough for almost all of us; that is 97-98% of healthy New Zealanders.
Nutrient reference values for Australia and New Zealand were published on 3 May 2006 and the full documents are available on the Ministry of Health website.
As well as preventing vitamin and mineral deficiencies, the latest recommendations also aim to combat the major killers in our society today – such as heart disease and cancers. For the first time, ‘suggested dietary targets’ (SDTs) have been included for the antioxidant vitamins, A, C, E and folate. These higher recommendations are based on amounts shown in research to help prevent these chronic diseases.
Amazingly, we still see New Zealanders going short of some vitamins and minerals. The most common is iron, a mineral not easily absorbed by the body. Others include folate, calcium, iodine, vitamin D and selenium. The selenium content of New Zealand soil is particularly low, which is reflected in the lower amounts available in our food. Those in the North Island obtain more selenium from bread made from imported Australian wheat, but ‘Mainlanders’ still rely on other dietary sources, such as seafood, meat and eggs.
Our soil is also low in iodine, so we rely on this important mineral being added to our table salt. This has been done since the 1920s, helping to overcome our previously high rate of goitre. The consumption of iodised salt has decreased in more recent times, as has the use of iodine in the production of dairy products, and the government is, once again, faced with considering mandatory fortification of another food.
Some New Zealanders are also beginning to go short on vitamin D. This may be due, in part, to the increasing awareness of reducing time spent in the sun, so dietary sources are becoming increasingly important.
Times when some people need a little more than the ‘norm’
|Planning a pregnancy||Folate||To prevent neural tube defects occurring in very early pregnancy|
|Pregnancy and breastfeeding||Most vitamins and minerals||To nourish the growing foetus and newborn, in addition to fulfilling mother’s own needs|
|Teenagers||Iron, calcium||Time of rapid growth|
|Endurance athletes||Iron, vitamins B, C and E||Increases losses through physical demands on the body|
|Vegans||Vitamin B12, iron and zinc (calcium)||Vitamin B12 is only found in animal foods; iron and zinc used less easily from plant sources, estimated to need 80% more iron and 50% more zinc|
|Older people||Vitamin D if housebound; vitamins B2, B6, B12, E and folate, zinc, calcium and iron||Less sun exposure, so less ability to make D; less efficient use of nutrients in the body|
|Recovering from illness or surgery||Zinc, vitamin C||For wound-healing or fighting infection|
All is not equal
Minerals are generally fairly reticent about making themselves available to us, especially when combined with certain foods or components of the same food. On average, only about 18% of the iron we eat is actually taken up into the body where it can be used. This is increased to around 25% when iron is eaten in meat and fish, but as low as 5% from spinach or cereals. These plant foods contain other components such as fibre, phytates and oxalates, all of which reduce iron’s availability. The tannins in tea do as well, so avoid drinking tea with your meals. Try fruit juice instead; the vitamin C helps us to absorb more of the iron. The use of zinc is also affected by phytates (found in cereals, legumes and nuts). The new Ministry of Health recommendations reflect these differing rates of availability, suggesting those avoiding meat and fish may need up to 80% more iron and 50% more zinc than meat eaters.
In contrast, vitamins are all too willing to give themselves up. Water-soluble vitamins are particularly sensitive to heat and light. 25% of vitamin C can be lost when boiling potatoes or other vegetables in just a few minutes. In many fruits and vegetables, the highest concentration of this vitamin is found just under the skin, so try to eat them with the skins on. Also cook them for the minimum amount of time. The ideas of chefs and nutritionists don’t always coincide, but the trend for serving vegetables ‘al dente’ is not only fashionable but good for us too! Having fresh fruit and vegetables hanging around for days reduces the vitamin content. Try to eat them within a few days, or consider using frozen or canned varieties. They are frozen or canned fresh and offer a nutritious alternative; especially when access to fresh produce is limited or it’s not in season. In the days when daily milk deliveries in glass bottles were common, a good deal of the vitamin B2 was lost in the morning sun if the recipient was enjoying a lie-in. While we might lament the loss of the milk bottle, cartons do seem to offer a nutritional advantage.
Keep the car running smoothly
You might think eating enough vitamins and minerals from food is complicated. But when we look at the variety that is found in everyday foods, such as cereals, fruit, vegetables, meat and fish, be reassured. If you are eating three meals a day, with a reasonable smattering of these major food types, you have every chance of including all 28 of the nutritional nuts and bolts. Not only that, but also great taste, pleasure and enjoyment, ensuring your engine is running smoothly.
Top sources of vitamins and minerals
- Meat – Vitamin B1 (pork), vitamins B2, B6, B12, niacin, iron, magnesium, sodium (cured meat), chromium, selenium and zinc
- Seafood – Vitamins A and D, calcium (oily fish), vitamins B2, B12, niacin, potassium, copper, iodine, selenium and zinc
- Kiwifruit, citrus fruit and tomatoes – Vitamin C and potassium
- Red and orange vegetables (carrots and capsicum) – Beta-carotene and vitamin C
- Green vegetables – Vitamin B2, B6, C, K, niacin, folate, iron and magnesium
- Dried fruit – Calcium, iron and potassium
- Milk, yoghurt and cheese – Vitamins A, B2, B12, D, K, niacin, calcium, magnesium, potassium, sodium, chromium, iodine and zinc
- Nuts and seeds – Vitamins B1, B2, B6, E, calcium, magnesium, potassium, sodium (salted nuts), copper, selenium and zinc
- Legumes/beans – Vitamin B1, iron and zinc
- Liver and kidney – Vitamins A, B1, B2, B6, B12, K, niacin, folate, iron, chromium and copper
- Wholegrain breads and fortified breakfast cereals – Vitamins B1, B2, B6, K, niacin, folate, calcium, iron, magnesium, chromium, copper, selenium and zinc
- Eggs – Niacin, vitamins A, B12, D, K, iron, chromium, iodine, selenium and zinc
- Yeast extract – Vitamins B1, B2, potassium, sodium and chromium
Vitamins and minerals interact with each other. Some of these relationships are beneficial and essential for optimum health. For example, calcium needs vitamin D; iron works with vitamin B12; vitamins C and E work with selenium as a powerful antioxidant team. These recipes highlight good interaction of vitamins and minerals:
- Beef with orange sauce – Stir-fry 300g lean beef until evenly browned. Add a finely chopped onion with 2 teaspoons of oil. Stir-fry until softened. Stir in a tablespoon of tomato purée and cook for 2 minutes. Add a cup of mixed vegetables and stir-fry for 2 minutes. Pour in 1 cup of orange juice and heat through. Thicken with a little cornflour if desired. (A good source of iron with vitamin B12 to enhance its absorption.)
- Quick salmon pâté – Flake a 210g can of salmon, drained, mix with 120g cottage cheese with garlic and herbs. Add a squeeze of lemon juice and season with salt and pepper. Serve on crackers or bread. (A good source of calcium and vitamin D.)
Shortly after discovering vitamins, scientists started to make them artificially, the first being vitamin C in 1935. Since then, the market for vitamin and mineral supplements has grown steadily into a multi-million dollar market.
Some people use supplements as an insurance policy if they have concerns about their diet. Supplements can have a role but they can’t fully compensate for a poor diet and they won’t give you the long-term health advantages you get from eating well. The best insurance policy is to eat a wide variety of healthy foods.
A role for supplements
There are a few times when we need particularly high amounts of some vitamins and minerals, or when, for other reasons, we struggle to obtain enough from our food. These are a few specific times when a supplement might be needed:
- Folate – As well as eating foods rich in folate, women planning to become pregnant and in the early stages of pregnancy are advised take an 800μg (0.8mg) folic acid tablet for at least 4 weeks before and 12 weeks following conception, to reduce the risk of neural tube defects in the foetus. For women with an increased risk of a pregnancy affected by a neural tube defect, a 5000μg (5mg) tablet is recommended.
- Iron – When there is evidence of low iron stores or iron deficiency anaemia, iron supplementation will be prescribed. Vegetarians, women with high menstrual losses and pregnant women are susceptible to low iron. Side effects of supplementation can be uncomfortable so try to eat an iron-rich diet to avoid the need.
- Calcium – Supplements may be needed by people who are unable to consume enough in their diet, although milk and soy alternatives with extra calcium are now widely available. Older women at high risk of fracture may be advised to use supplements.
- Vitamin B12 – As vitamin B12 is only found in animal products, vegans must consume foods fortified with vitamin B12 or take a supplement. Dairy products are a good source for vegetarians. Older people, as well as people with pernicious anaemia or those who have had gastric surgery do not absorb vitamin B12 efficiently and may become deficient. Medical advice must be taken in these instances as a correct diagnosis is needed; B12 supplementation can mask other problems.
- Vitamin D – Our bodies can make all the vitamin D we need with exposure to the sun: just 10-15 minutes on hands and face each day for fair skinned people and up to 30 minutes if you’ve dark skin. For those with reduced exposure to the sun and older people whose ability to make vitamin D is reduced, supplementation may be advised.
- Multivitamin/mineral – It can be tempting to think of a multivitamin and mineral supplement as an ‘insurance policy’ but when you eat a limited diet it’s not just vitamins and minerals you’re missing out on, so you’d be kidding yourself if you thought a tablet could make up for a poor diet. Some older people with very low intakes of food may need a general multivitamin and mineral supplement. However, it is very important to discuss with a medical professional first as older people are often on medications that can interact with supplements.
Too much of a good thing is a bad thing!
Putting food first by eating a balanced and varied diet ensures you’re unlikely to consume too much of any particular vitamin or mineral.
With some nutrients, an ‘upper level of intake’ (UL) has been set by the Ministry of Health where it is known high intakes can be harmful to health. The UL is the highest average daily nutrient intake level likely to pose no adverse health effects to almost all individuals in the general population.
Some nutrients which we cannot live without can be a risk to health at high intakes on a daily basis; these include vitamin A, vitamin D, iron and selenium. So while we need these nutrients, more is not better!
- Fat-soluble vitamins are stored and too much can cause harm. Excessive amounts of vitamin A can damage your liver or your unborn child; and large amounts of the beta-carotene (found in foods such as carrots) can turn the skin a disconcerting yellow colour.
- If we take in more of the water-soluble vitamins B and C than we need, the excess may be flushed down the loo. Mega-doses of vitamin C (over about 2000mg/day) can cause diarrhoea and stomach cramps.
Supplements can supply controlled amounts of desired nutrients, but:
- not in the most available form
- there is the possibility of taking too much
- they are not in the combinations often needed for vitamins and minerals to work most effectively: and they are rarely required in isolation
- they can’t make up for a poor diet, a lack of sleep, inactivity or an over-stressed lifestyle
- there are literally hundreds of compounds occurring naturally in food, called phytochemicals, that may enhance our health, not just the specific vitamins and minerals that scientists have been able to replicate in tablets.
Always ask for advice
In some circumstances, supplements can be harmful even at normal doses. Inconsistent use of vitamin C can interfere with the oral contraceptive pill. Vitamin K neutralises the effect of warfarin (the blood-thinning drug) as vitamin K is particularly good at clotting blood. These negative effects aren’t limited to supplements though. A recent case of this conflict was seen with the launch of a new fortified milk product containing so much vitamin K, warfarin users have been told to consult their doctor before trying it.
A similar food example is seen with grapefruit juice. Whilst a rich source of vitamin C, grapefruit juice interferes with certain drugs used by those with high blood cholesterol levels as well as sleeping tablets.
If you decide to use supplements, remember the following:
- If you are on medication, check with your pharmacist or GP before taking any supplement.
- Take as directed and never more than suggested.
- ‘Supplement’ means a part which ‘adds to’ or ‘provides further’, so should only be taken in addition to a healthy balanced diet, not in place of eating well.