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?

All is not equal

Minerals

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.

Vitamins

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.

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.

There are times when you might need a little more than the ‘norm’: