Dr Michelle Fitzmaurice Registered Nutirtionist

Each Nutrition Basics Blog focuses on an aspect of human nutrition from nutrients to how food influences disease and health. In this post, you will learn about what calcium is and how is it used within our body.  You will also learn which food are excellent sources of calcium and which are also easily absorbed by the body. Finally, You can read about what other factors impact our overall calcium balance within our bodies.

 

What is calcium

Calcium is a mineral which accounts for 1 to 2% of an adults total body weight.  The majority of calcium is stored in our bones and teeth, with the remainder being stored in within our tissues, blood and the fluid surrounding our cells.

Why is calcium used for in the body?

As already mentioned calcium is mostly present in our bones, therefore helps us maintain our structure.  For the majority of people, our bodies lay down the majority of bone mass between 19 years of age to 30, so this is a critical time to ensure that we have enough calcium present to lay down that strong bone mass forming dense strong bones.

Because the structure of our bones is somewhat “dynamic”, there is a constant breaking down and forming of our bone structure, with calcium being removed to other areas of the body as required, and being redeposited in the bones for storage when required.

After 30 it is important to have enough calcium to maintain what is already present.   In this later stage in life, there is more breaking down of bone than there is building, so having adequate calcium intake is really important to help maintain strong bones and so limit the impact that falls can have on us as we age.

While there is significantly less calcium present in our bodily fluids, the role of calcium there is no less important.  Calcium is required for the production of thyroid hormones – and so has a role in maintaining our metabolism.  Calcium is also required for our muscles to contract and extend correctly AND is required for our nerves to carry impulses correctly!!

We really couldn’t function well if we didn’t have enough calcium.  In our daily lives, some calcium is lost from the extracellular fluids and our blood via the kidneys, so again it is important to replace these losses.

What are the food sources of calcium?

Calcium is not widely available in foods.  For the most part, good sources of calcium which are readily used by the body are found in milk, and milk products, such as cheeses and yogurts.

While green leafy vegetables provide a good source of calcium, it is currently believed that little is absorbed by the body.  This is due to other compounds naturally present in vegetables, called oxalates, phytates, tannins.  However not all calcium sources from vegetables are poorly absorbed and researchers are investigating whether these vegetables have other compounds which increase calcium absorption.

Vegetables such as  Bok Choy, Chinese cabbage, Chinese mustard, broccoli, and kale are absorbed as well, if not better than dairy products.

In the table below (Adapted from Weaver et al 1999) you can see the comparison of dairy and vegetable sources of calcium.  Shown is the amount of serves of each food which is equivalent to 300 mg of calcium (which is that found in a glass of milk).

It is suggested that across the lifespan 1000 mg of calcium daily,  is adequate to maintain health, increasing to 1200 mg in adults over 5o years of age.

For interest, I have also included the approximate absorption of calcium compared to what is available in the foods.  In this you can see that for some vegetables, such as spinach and rhubarb although they are good sources of calcium, this is not readily available to the body due to poor/ limited absorption.

Food Serving size (g) Calcium content per serve (mg) Estimated absorbable calcium (mg) Servings needed to equal 240 mL milk Percentage absorption %
Milk 240 300 96.3 1 32
Pinto Beans 86 44.7 11.9 8.1 27
Red Beans 172 40.5 9.9 9.7 24
White Beans 110 113 24.7 3.9 22
Bok choy 85 79 42.5 2.3 54
Broccoli 71 35 21.5 4.5 61
Cheddar cheese 42 303 97.2 1 32
Cheese food 42 241 77.4 1.2 32
Chinese cabbage flower leaves 85 239 94.7 1 40
Chinese mustard greens 85 212 85.3 1.1 40
Chinese spinach 85 347 29 3.3 8
Fruit punch with calcium citrate malate 240 300 156 0.62 52
Kale 85 61 30.1 3.2 49
Spinach 85 115 5.9 16.3 5
Sweet potatoes 164 44 9.8 9.8 22
Rhubarb 120 174 10.1 9.5 6
Tofu with calcium 126 258 80 1.2 31
Yogurt 240 300 96.3 1 32

 

 

Are they any other factors which may affect the calcium in my body?

Vitamin D

Calcium uptake in the gut is dependent on vitamin D!  Vitamin D is a vitamin but also acts as a hormone within the body.  I’ll write more about vitamin D soon – but in a nutshell – limited vitamin D, limited calcium taken in by the body.

High salt

It is suggested that additional sodium/salt intake can cause an increase in the loss of calcium from the body.  This is due to the fact that sodium (salt) and calcium are transported in the kidneys by some of the same cell transporters.  So when the kidneys attempt to remove the excess salt from the body, it draws the calcium with it.

Proton pump inhibitors

There is a lot of research investigating the role of proton pump inhibitors and the concern that they may lead to a decrease in calcium absorption which may, in turn, impact skeletal structure.  Proton pump inhibitors are routinely prescribed for acid reflux.  If you are currently taking medication for this and are concerned, please have a chat to your medical team for further advice.