Minerals are substances which occur in nature, in water, rocks or soil. They make their way into plants, then into animals so they're present throughout human diets.
One of the major minerals is calcium; in fact, it's the most plentiful in your body, making up 40% of the body's total mineral content.
99% of the body's calcium is in your bones and teeth and the remaining - very important - 1% is in the blood.
Where can I get it?
Good food sources of calcium are:
- Milk, hard cheese and other dairy products (except butter)
- Geen leafy vegetables, like broccoli and cabbage but not spinach
- Soya bean products, such as tofu and soya milk with added calcium
- Bread (in the UK all flour, except wholemeal flour, has added calcium, and wholemeal flour naturally contains calcium)
- Almonds, Brazil nuts and hazelnuts
- Fortified breakfast cereals
- Fish like sardines and pilchards (because you eat the bones)
How much should I eat?
The amount of calcium you need depends on your age and also your sex.
Children's needs increase as they grow and adolescents need more than adults, particularly boys, because of the rapid growth of the skeleton.
Less than half the calcium you consume is absorbed, so the guidelines take that into account. It's recommended that adults consume 700mg per day.
You don't need to consume more during pregnancy, although an extra 550mg per day is recommended if you're breastfeeding.
What does 700mg look like? Here are some examples...
- 2 slices wholemeal toast: 77mg
- 30g (matchbox-size piece) cheddar: 222mg
- Low fat natural yoghurt (125g): 203mg
- Small handful plain almonds: 24mg
- 100g canned sardines in tomato sauce: 430mg
- 100g steamed tofu: 510mg
- A portion of cooked broccoli: 32mg
It's quite easy to get all the calcium you need by eating a varied and balanced diet. The Food Standards Agency recommends that, if you do take supplements, you shouldn't take more than 1500mg per day. Higher doses can cause stomach pain and diarrhoea.
Consuming high levels of calcium may also make it more difficult for your body to use iron from the diet, and perhaps other minerals, such as zinc.
What does it do?
Some of calcium's main functions are concerned with muscle contractions, including the heartbeat, and helping to make sure blood clots normally. These roles account for just 1% of the calcium in the body but they're so important that your body will break down your bones to get at the calcium it needs.
Calcium is mainly found in bones, which act as a sort of ‘reservoir' for calcium. When your body needs calcium elsewhere, it will be taken from your bones, then replaced it later. This means that bones are usually maintained at a similar level.
However, as we age, there are changes to our hormones which affect the amount of calcium being replaced in bones. This particularly affects women after the menopause and, as the bones become weaker because the calcium isn't replaced, can result in osteoporosis.
Osteoporosis usually affects older women after the menopause because they have less of the protective hormone called oestrogen. The risk of fractures increases because your bone density (bone strength) reduces over time.
Diet and exercise are involved in the development of osteoporosis as well as other factors, like smoking.
It's particularly important that teenage girls and young women eat calcium-rich foods, stay physically active and maintain a healthy weight to reduce their chance of developing osteoporosis later in life.
Weight-bearing exercises such as regular, brisk walking or climbing stairs are excellent ways to help keep your bones healthy. If you haven't exercised for some time, or have had a bone fracture in the past, speak to your GP before you start exercising.