Dietary Calcium: Balance Loss of Calcium by Increasing Intake of Bioavailable Calcium for Improved Calcium Absorption
Calcium Requirements
A minimum average daily intake of 1200mg dietary calcium is recommended by most health authorities for optimal bone strength in women, and this is especially important in teenage girls, postmenopausal women and women approaching menopause. Currently dairy products offer the best source of calcium, however many people cannot tolerate dairy foods and may not obtain sufficient amounts of calcium as a result. Others may be unknowingly causing loss of calcium from the body through suboptimal food combinations or lack of awareness of the importance of choosing bioavailable calcium. Calcium deficiency often leads to osteoporosis in postmenopausal women as well as other health problems.
Eating Your Greens May Inhibit Absorption of Calcium
Although many people believe that they are consuming the recommended daily allowance of dietary calcium either through dairy consumption or supplements, most people still do not take into account factors that limit the ability of their body to absorb that calcium. Vegetarians and vegans are at particular risk of low calcium absorption because most plant sources of calcium are not usable due to the antagonistic properties of oxalate and phytate which inhibit calcium absorption. However some green vegetables, such as kale, broccoli and bok choy, are very good sources of bioavailable calcium due to their low oxalate content.
Soy Contains Bioavailable Calcium
Paradoxically, soy bean products are valuable sources of bioavailable calcium despite their high oxalate and phytate levels. Soy foods have received both positive and negative press over recent years; positive due to their high nutritional value, but negative due to the phytoestrogen content linked in some studies to certain cancers and hormonal disturbances.
Factors Preventing Absorption of Calcium
Despite the wide availability of choices for obtaining beneficial sources of calcium, including a vast range of supplements, there are some very common causes of calcium loss from the body. Calcium can be excreted from the body in large quantities by a high salt intake, caffeine and even protein. In our modern society it seems impossible to avoid these factors entirely, but we can limit our intake of salt and caffeine, and also regulate consumption by paying attention to food combination.
The Effect of Salt
Excess sodium in table salt is excreted by the kidneys taking with it significant quantities of calcium. Therefore high salt diets increase the loss of calcium loss and risk of osteoporosis. It is recommended that, for a daily intake of 1200mg dietary calcium, no more than 2.3g sodium be consumed.
Balancing Protein and Calcium
Protein consumption and its inhibitory effect on calcium absorption is a problem for both vegetarians and non-vegetarians. Sulfur-containing amino acids are the worst offenders which are found in high quantities in meat products, nuts, seeds and cereals; therefore avoiding sulfur-containing protein sources can be difficult. A calcium to protein ratio of 16:1 has been recommended as an alternative to reducing protein consumption particularly for vegetarians.
Calcium Supplements
In general it seems that a normal healthy diet will decrease the ability of our body to absorb enough bioavailable calcium for optimal bone health. Consequently the easiest course of action for the average individual may be to consider a high quality calcium supplement. Calculation of appropriate dosage depends on individual circumstances. People who consume high levels of salt, vegetables high in oxalate and phytate, and protein rich in sulfur may need to increase their calcium supplement to exceed the daily average recommended level in order to counteract the loss of calcium.
References
Weaver CM, Proulx WR and Heaney R, 1999, Choices for achieving adequate dietary calcium with a vegetarian diet, American Journal of Clinical Nutrition, vol 70, no. 3, p543S-548S.
