Almost all of the calcium in your body is found in bones, with only a little freely in the blood. But if the blood has too little calcium, it has to renew its stock and the obvious source is your bones. When this happens, bones weaken. As this process occurs daily it is important to maintain bone mass and prevent bone loss by consuming enough calcium every day. Dairy products are a source of bioavailable calcium, which is easily absorbed by the body in the presence of vitamin D. 

Why Calcium?

• We need calcium for building and maintaining strong bones.
• Dairy products are a source of calcium in the diet.
• Dairy calcium is particularly well absorbed and thus bioavailable.
• To ensure optimal bone mass development, children need to consume enough calcium during the growth phase. Low bone mass is associated with a higher fracture risk – in children as well as in adults – and can lead to osteoporosis later on in life.
• Dietary calcium enhances the effect of physical activity on bone mass during growth
  

Where do you get calcium?

REMEMBER! Strong bones and teeth need calcium.

Dairy products such as milk, cheese, maas and yoghurt are sources of calcium. Other sources of calcium include sardines, salmon, spinach, cabbage, broccoli and beans.

Calcium absorption

• The human body contains about 1.2 kg calcium.
• Your body absorbs only about a third of the calcium in dairy products, depending on your calcium status. It is therefore crucial to consume enough calcium daily and everyone can benefit from increasing their daily calcium intake. Calcium recommendations do, however, take into account natural losses and rates of absorption.

 Dietary factors that enhance calcium absorption

• Stomach acids
  1. An acidic environment in the gastrointestinal tract is required for calcium to be absorbed. Stomach acids help to keep calcium soluble.
• Vitamin D and growth hormones
  1. Adequate vitamin D promotes calcium absorption as it helps make calcium-binding proteins needed for absorption.  Calcium absorption in the blood is regulated by vitamin D and several hormones – calcitonin, parathyroid hormone, 1,25-dihydroxycalcitron and oestrogens. 
• Physiological state
  1. Calcium has to be in a water-soluble form to be absorbed. Approximately one third of calcium in dairy is in a water-soluble form and is therefore particularly well absorbed. The rest of the calcium in milk is bound to casein and is made available by enzymes in the stomach and intestines. 
  2. The phosphopeptides and lactose in milk further facilitate absorption of calcium.

Factors that inhibit calcium absorption

• Too little stomach acid.
• Vitamin D deficiency due to limited exposure to sunlight and low intakes of vitamin D.
• Oxalates. Calcium in plant material, such as spinach and broccoli, is only absorbed to a limited extent as the vegetables contain substances that render calcium insoluble in water. Absorption of calcium is inversely associated with the oxalic acid content in food. The bioavailability of calcium in foods with a high oxalate content such as spinach and rhubarb is low, while vegetables such as cabbage, broccoli and Brussels sprouts, with a low oxalate content have more bioavailable calcium.
• High phosphorus intake.
• Sodium (salt) increases calcium excretion.
• Dietary fibre. When consumed in large amounts, wheat bran can inhibit the absorption of calcium consumed at the same time, although the effect is relatively small.
• Absorption of calcium is inversely associated with oxalic acid content in food
•  Phytates present in beans, seeds, nuts and grains. Three cups (750 ml) of cooked red beans or 2 cups (500 ml) of cooked spinach need to be consumed in order to obtain the same amount of calcium as in one cup (250 ml) of milk

Non-dietary factors affecting calcium metabolism

• Age and oestrogen status:  Calcium absorption efficiency drops by about 20% between the ages of 40 and 60 owing to the combination of increasing age and oestrogen withdrawal.
• Pregnancy and lactation:  During pregnancy, intestinal calcium absorption increases from 27% before pregnancy to 54% during the fifth or sixth month of pregnancy and to 42% at term.  There is a temporary loss of calcium from bone during lactation, independent of calcium intake, but after weaning the efficiency of intestinal calcium absorption and renal retention increases.

Based on the Nutrient Reference Value (NRV), the minimum requirement of calcium for individuals of 4 years and older is 1300 mg per day.

The table below shows how much of certain products you would need to consume to get the same amount of calcium (approximately 300 mg per serving) as from 250 ml milk: