Calcium

Last updated 12 April 2016 — Last reviewed 15 December 2013

How important is calcium to our bones? You will also find information on the changes that happen to bones as women age, the recommended daily calcium intake for women at different ages, the calcium content of different foods and types of calcium supplements.

The importance of calcium

Calcium is one of the essential nutrients necessary for healthy bone development. Bones contain most of our body’s calcium, so they act as the body’s 'reservoir' of calcium. Calcium is critical for the function of cells in the body and a certain amount of calcium circulates within the blood, with the body maintaining the levels of calcium within a very tight range. Our bodies cannot make calcium, and if blood calcium levels fall, the body will compensate for this by drawing calcium out of bones and putting it into the blood. Calcium is also excreted by the body daily.

This means it is important to have an adequate daily intake of calcium through your diet, so your bone mineral strength is not compromised.

Woman drinking milk

Recommended daily calcium intake

There are critical times in life when it is vital to ensure that calcium intake through food and/or supplements is adequate and meets the recommended requirements. The following table lists these requirements:

Who Age Recommended daily calcium intake Bone health issues
Children 1-3 500mg During this growth phase the foundations for peak bone mass are laid, so it is essential calcium intake matches the needs of growing bones.
  4-8 700mg
Girls 9-11 1,000mg
  12-18 1,300mg
Women 19-50 1,000mg
  • Between 20-30 years bone gain and loss is quite stable – a healthy lifestyle during these years supports good bone health
  • From the mid-30s onwards, bone loss starts to increase more than bone gain
  50+ 1,300mg
  • When women go through menopause, there is a rapid loss of bone because of  decreased oestrogen and this process may last from 4-8 years after menopause
  • After this period of time the rate of bone loss is reduced and stabilises
  • The gastrointestinal system and kidney become less efficient at absorbing and conserving calcium in the body and this creates a state of potential calcium loss in the blood so the body compensates for this by drawing calcium out of the bones
  • The reduced exposure to sunlight and lower vitamin D levels of many women over 50 can reduce the absorption of calcium for bone strength
Pregnant and lactating women 14-18 1,300mg
  • Pregnant women and breastfeeding women have higher requirements for calcium to be absorbed through the mother’s gastrointestinal system. The calcium is needed to support:
    • skeletal growth of the foetus
    • milk production
  • Normal pregnancy and breastfeeding is associated with a certain amount of bone mineral loss, which generally recovers 6-12 months after birth and/or stopping breast feeding[1]
  19-30 1,000mg
  31-50 1,000mg

Source: National Health and Medical Research Council. (2006) NZ

Calcium content of various foods

While dairy products can provide a good source of calcium, daily calcium requirements need not necessarily come only from dairy products. Two serves of dairy and another serve of calcium-rich foods like broccoli, beans, almonds, tinned salmon and sardines equate to about 1,000mg of calcium.

Food sources of calcium

If you choose alternative calcium sources, note the quantity of calcium found within the particular food source. The following table lists the average calcium content of a variety of foods:

Food Serving Calcium per serve
Regular milk 1 cup (250ml) 285mg
Skim milk 1 cup (250ml) 310mg
Natural yogurt 1 tub (200g) 340mg
Low fat yogurt 1 tub (200g) 420mg
Cheddar cheese 40g cube 310mg
Low fat cottage cheese 100g 80mg
White bread 1 slice 15mg
Cooked spinach 1 cup (340g) 170mg
Cooked broccoli 1 cup (100g) 30mg
Canned salmon (+ bones) ½ cup 230mg
Canned sardines (+ bones) 50g 190mg
Almonds 15 almonds 50mg
Tofu 100g block 0-100mg*

* The calcium content of tofu depends on how the tofu has been processed. If it is processed using calcium chloride or calcium sulphate, tofu may have up to 100mg calcium per 100g block. Otherwise the calcium content of tofu is very low.

Calcium Counter - Reproduced with permission from Dairy Australia (as per Calcium Fact Sheet) – last updated 17/7/2002.

Calcium supplements

Calcium needs are generally best met through diet. However, calcium supplements may be required by those who do not obtain adequate calcium from food products to meet the 1,000-1,300mg per day required for girls and women.

Most calcium supplements in Australia contain:

  • calcium carbonate (sold as caltrate) or
  • calcium citrate (sold as citracal)

Calcium carbonate

Caltrate requires an acidic environment for maximum absorption and should be taken with meals.

Calcium citrate

Calcium citrate does not require an acidic environment and therefore can be taken on an empty stomach (but is better taken with food). It is the preferred calcium product for people who need to take anti-reflux medications.

When to take calcium supplements

It is best to take calcium supplements at night, as this is when bone 'turnover' increases.

It's important not to overdose on calcium supplements, as very high calcium intake (2,400mg/day) has been linked with heart disease.

References

  1. Tran HA, Petrovsky N. Pregnancy-associated osteoporosis with hypercalcaemia. Int Med Journal 2002;32:481-5.

This web page is designed to be informative and educational. It is not intended to provide specific medical advice or replace advice from your health practitioner. The information above is based on current medical knowledge, evidence and practice as at December 2013.

Subscribe To our newsletters