The Bone Builder: Calcium

Calcium pills on a spoon.Calcium Benefits

Calcium is one of the most abundant minerals in the body.  Most of the calcium is stored in bones and teeth. This mineral is tightly regulated, if not enough calcium is available through your diet or supplements, calcium is pulled from the bones or teeth, not what you want to happen.

We need calcium throughout our lifetime and for different reasons.   During childhood and adolescents we need calcium to help build and form bone and start a reservoir for later years, breakdown occurs at a much lesser rate.  As adults the build-up and breakdown of bones is about equal, so we need calcium to help maintain this balance.  When we reach our 40’s the breakdown of bones exceeds the build-up, which can result in osteopenia or osteoporosis.    Therefore, regardless of age it’s important you are getting enough calcium either through your diet or by taking supplements.   Besides bone growth, calcium is needed to help build and maintain teeth, it helps regulate the heartbeat, it helps blood vessels move blood throughout your body, it helps contract muscles, it transmits nerve messages of the brain throughout the body and it helps release hormones and enzymes.

The Institute of Medicine makes the following RDA for calcium:

1-3 yrs old         700 mg/day

4-8 yrs old        1000 mg/day

9-18 yrs old      1,300 mg/day

19-51 yrs old    1,000 mg/day

51yrs                  1,200 mg/day

Good food sources of calcium

Plant-based Sources:

Beans, tofu (made with calcium sulfate), spinach, kale, rhubarb, bok choy, sardines, Black-strap molasses, Almonds, Orange juice (calcium fortified)

Animal-based Sources:

Milk, yogurt, cheese, cottage cheese, ricotta cheese, buttermilk

What to look for when supplementing for calcium

There are two forms of calcium supplements:

  1. Calcium Carbonate
  2. Calcium Citrate

Calcium Carbonate is best absorbed with food, whereas calcium citrate can be taken with or without food. They both vary in the amount of elemental calcium they contain, calcium carbonate has 40% calcium by weight and calcium citrate has 21%.  These amounts will effect how much calcium is absorbed at one time.  The higher the amount of calcium the less calcium is absorbed.  So, in this case more is not better.  Calcium is best absorbed in amounts less or equal to 500 mg.  For example, if you need 1000mg, take one 500mg supplement at breakfast and another 500 mg at lunch or dinner.

The Role of Exercise

Exercise, especially weight bearing exercises, help maintain and retain bone density.  The stress on the bone signals cells in the bones to respond by making the bone denser and stronger. 

Weight bearing exercises include strength training, running, walking, stair climbing and racquet sports. 

Vitamin D

In order to effectively absorb calcium, vitamin D needs to be present.  If you are low in Vitamin D you are most likely deficient in calcium as well.


Estrogen helps absorb calcium, if estrogen levels are low, which is what happens after menopause,  calcium absorption drops as well.

Foods that inhibit calcium absorption:

Oxalic acid also called oxalate, is one of the strongest inhibitors of  calcium absorption, it can be found in spinach, rhubarb, and in lesser amounts in sweet potatoes and dried beans.  Another inhibitor but somewhat less potent is Phytic acid which can be found in fiber containing whole grains, wheat bean, beans,seeds, nuts, and soy isolaes, the yeast used in baked goods contains phytase which helps break down the phytic acid.

Calcium also decreases iron absorption from non-heme sources such as plant foods and supplement and should be taken 2 hours apart.

Tannins which can be found in tea can bind with calcium in the intestine and can inhibit its absorption.


Long-term use of corticosteroids and anti-convulsants can affect bone health. 




Linus Pauling Institute Micronutrient Research for Optimum Health.

Office of Dietary Supplements:  National Institute of Health.

Harvard School of Public Health.  Then Nutrition Source: Calcium and Milk:  What’s the Best for Your Bones and Health.  Accessed April 29, 2011.



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