What does calcium do for our bodies?

GOOD FOR THE BONES: Ciaran Harper enjoys a glass of milk.
GOOD FOR THE BONES: Ciaran Harper enjoys a glass of milk.

"I would like to know some details about calcium supplements. I know they are useful for bones, but if I don't take supplements I get restless sleep and night frights. I have taken magnesium alone, but that doesn't work so well. Hope you have some answers." Val

Calcium is certainly an essential mineral, primarily important for building strong teeth and bones. However, it does have other roles. It helps blood to clot, nerves to function, muscles to contract and relax, and certain hormones to be released. Every day, one third of the calcium stored in our body leaves our bones and needs to be replenished from the food we eat or we will become deficient. This is especially important in growing children and the elderly.

The long-term risks of not having enough calcium include:

Thinning of your bones, leading to osteoporosis;

Rickets in children, which can affect bone growth and cause bony deformities;

Muscle cramps and spasms, facial twitching or weak muscles;

Irregular heart rhythms and clotting problems.

Regarding your comment about poor sleep and night frights, there is as yet no definitive link between calcium and sleep.

However, it is known that calcium levels fluctuate during the day and night, and they are associated with muscle cramps and spasms, so perhaps that is affecting your sleep patterns. Magnesium that you also mention is more promising in terms of sleep benefits.

A study in 2010 suggested an association between magnesium status and sleep quality, but the authors concluded that further research was needed. Regardless of how well you sleep, it is important to ensure you have enough calcium. But how much is enough?

The recommended daily intake for adults is approximately 1000mg. Children require 200mg to 800mg daily, depending on their age. Interestingly, teenagers actually have higher needs than adults, requiring around 1300mg a day, presumably due to their high growth rates.

It is estimated that many New Zealanders (especially vulnerable teenage girls) are falling short of this recommended daily limit. This is worrying as inadequate calcium consumption during adolescence and early adulthood will lead to compromised bone strength and density in later life. Those most at risk of calcium deficiency in New Zealand include growing children, the elderly, pregnant and breastfeeding women, vegans, and anyone who is severely underweight.

The following foods are the richest dietary sources of calcium:

Milk and other dairy products - skimmed can actually contain more calcium than whole milk, and is obviously a better option in terms of the fat content

Green leafy veges - broccoli, silverbeet, bok choy

Fish - especially canned with bones (salmon, anchovies, sardines, whitebait)


Nuts - almonds, brazil nuts, sesame seeds


Some foods are fortified with calcium, to help people who are unable to achieve their calcium intake any other way (for example, bread, some juices). However, studies have shown that fortified calcium is not as well absorbed as calcium that occurs naturally in foods.

In terms of exactly how much you need to consume to reach your daily target, the following is a rough guide:

1 pot yoghurt (150mg) = 210mg calcium

1 glass of milk (200ml) = 240mg calcium

1 portion tasty/cheddar cheese (40g) = 300mg calcium

Muesli (50g portion) = 50mg calcium

4 apricots = 120mg calcium

Tinned salmon (100g) = 90mg calcium

Portion pasta = 85mg calcium

12 almonds = 60mg calcium.

Calcium absorption is also reduced by excessive amounts of certain foods, including spinach, rhubarb, tea, cocoa and chocolate.

It is possible to have too high a calcium intake, especially if you are taking supplements, so be cautious and talk to your doctor or a dietitian if you are concerned. Excess calcium in your system can lead to kidney stones, abdominal pain and vomiting.

Vitamin D is essential to the absorption of calcium, and vitamin D deficiency can lead to calcium deficiency as well. Some foods are rich in vitamin D, but it is largely obtained from sunlight. Most New Zealanders are likely to benefit from taking vitamin D supplements during the winter months.

Unfortunately, the medical jury is a little out at present regarding the use of calcium supplements, which are consumed by millions of people throughout the world.

A recent study has shown that people (especially those over 70 years old) on calcium supplements are at slightly increased risk of heart attacks. Why this happens is not yet fully understood.

The risk to any individual is actually pretty low, but because so many people around the world are taking calcium supplements the overall increase in heart attacks could be huge. At the moment, medical advice is unclear, but it is sensible to discuss with your doctor about whether you should come off your calcium supplements and try to obtain the calcium your body requires from your diet instead - in all likelihood a safer option, especially in the elderly. This advice does not apply to everyone, so please consult your doctor first.

Bearing this in mind, I would concentrate where possible on getting your daily intake of calcium from your diet rather than a supplement.

Irrespective of whether it may be helping your sleep, calcium will certainly be improving your bone strength, which for women especially is a major concern.

Cathy Stephenson is a general practitioner, medical forensic examiner and mother of three. If you have a question for her, write c/o Features Editor, The Dominion Post, PO Box 3740, Wellington 6140.

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