Calcium accounts for 1-2% of the human body weight. Over 99% thereof is in bones and teeth. The remainder is in the blood, in fluids between cells, muscles and other tissue, where it is used in many processes.1
Deficiency as well as too much calcium is associated with negative consequences. But usually deficiency is the problem.
Calcium is involved in many processes in the body. If the intake is not sufficient, then the body will take it from the bones and releases it into the blood stream, so that these processes continue to have enough calcium available1. Therefore, the calcium content in the blood is always about steady, disregarding if the calcium intake is sufficient or not.
In the short term a calcium deficiency does not show any symptoms2, because the body stabilizes the calcium blood value. Not enough calcium in the blood (hypocalcemia) develops mostly as a consequence of other medical problems or treatments, such as kidney failure, removing the gut, or some medications2. The symptoms are numbness and tingling in the fingers, muscle cramps, convolutions, lethargy, poor appetite, and abnormal heart rhythms2. Without treatment, hypocalcemia will lead to death2.
Over the longer term a too low calcium intake leads to calcium reduction in the bones, what can lead to osteoporosis (bone fragility). Is is to be noted, that not every bone fragility is the result of calcium deficiency, there can also be other causes3.
A too high calcium intake can have negative consequences. The most important and best researched are: kidney stones, hypercalcemia with renal failure, and absorption problems for other minerals.
The exact cause and effect relationships between calcium intake and kidney stones are not yet researched in detail. It could be possible that calcium absorbed from normal food even helps against kidney stones, but enhances the risk of stones if taken alone. Generally, it appears that a too high calcium intake together with other factors increase the risk of kidney stones.1
Hypercalcemia with Renal Insufficiency (Milk-Alkali-Syndrome or also Burnett-Syndrome)
The occurrence of hypercalcemia with or without following renal insufficiency (with or without alkalosis) is a serious condition, which covers almost all organs. A renal failure can be without permanent damage, if the underlying cause is quickly resolved. If nothing is done then calcium might start to accumulate in tissue, including in the liver, which can be deadly. The Institute of Medicine (US) has found in a literature research 26 cases which would match hypercalcemia with renal failure and these cases occurred at a calcium intake between 1.5 to 16.5 g per day over 2 days to 30 years.1
Interaction of Calcium with Other Minerals
The calcium absorption has effects on other minerals, like iron, zinc, magnesium, and phosphor. Calcium reduces the iron absorption. But there are no known cases of iron deficiency due to calcium supplementation. The exact interactions between calcium intake and other minerals are insufficiently researched. An excess calcium intake may be a risk especially if there is already a deficiency in another mineral.1
To sum up, it can be said that excess calcium intake is not researched in detail. Excess calcium intake can have negative consequences and, therefore, it is advisable to calculate in a way that the daily intake from food and supplements stays around the recommended daily intake and below the recommended maximum dose (upper level - UL).
Recommended Daily Intake (Total)The following amounts are recommended for daily consumption with normal food and include any supplementation. That the body only absorbs a fraction of all calcium is already accounted for.4.
The US Institute of Medicine (US 1997) recommends the following intake (adequate intake) :
|USA AI 1997|
|Infants 0 to 3 months||210 mg1|
|Infants 4 to 6 months||210 mg1|
|Infants 7 to 11 months||270 mg1|
|Children 1-3 years||500 mg1|
|Children 4-6 years||800 mg1|
|Children 7-8 years||800 mg1|
|Children 9 years||1'300 mg1|
|Children 10-12 years||1'300 mg1|
|Children and young adults 13-18 years||1'300 mg1|
|Adults 19-50 years||1'000 mg1|
|Adults 51-70 years||1'200 mg1|
|Adults 71 years and older||1'200 mg1|
|Pregnant 14-18 years||1'300 mg1|
|Pregnant 19-50 years||1'000 mg1|
|Lactating 14-18 years||1'300 mg1|
|Lactating 19-50 years||1'000 mg1|
The US Institute of Medicine has derived these values by analyzing studies of the effect of additional calcium on the bone mineral density. A higher bone minerals density is associated with less fractures, meaning stronger bones.
These values are applicable for healthy individuals without known kidney, liver, or other diseases.
Vitamin D is important for calcium absorption. If there is a vitamin D deficiency, then additional vitamin D can also improve the calcium absorption.
More detailed tables by age and gender are available here.
Assessment of Status
The calcium in the blood is tightly regulated by the body5. If there is insufficient calcium in the blood, then the body releases it from the bones until there is again a normal level of calcium. Given that, a blood test is not suited to detect calcium deficiency, because the blood level can be normal while more and more calcium is being taken out of the bones.
It is possible with help of dual-energy X-ray absorptiometry (DXA) to estimate the bone mineral density6. If it is low, then the question for the cause arises. If the reason is insufficient calcium absorption then a higher intake of calcium or vitamin D might be helpful. Vitamin D is important for calcium absorption.
For calcium absorption from natural food, in general, the calcium content is more important than the bioavailability. Calcium is about equally well absorbed in most foods.1
The table below shows the calcium content of some selected food:
|Cheese, Brie||184 mg||8|
|Cheese, Camembert||388 mg||9|
|Cheese, Gruyere||1'011 mg||10|
|Cheese, Parmesan||1'184 mg||11|
|Vegetables and Fruits|
|Lettuce, green||36 mg||14|
|Ground beef||13 mg||19|
|Bread (Wheat)||125 mg||22|
|* Calcium from spinach is not well absorbed due|
to the oxalic acid in spinach.
Calcium is not absorbed well from foods with high content of oxalic acid (spinach, sweet potatoes, rhubarb and beans) or high content of phytic acid (unleavened bread - e.g. prepared without fermentation, raw beans, seeds, nuts, grains and soy-isolate). But the calcium of soy beans is well absorbed.1
A vitamin D deficiency worsens the absorption of calcium in the intestine23.
If high calcium containing cheese is regularly eaten, e.g. Gruyere, then the recommended daily intake can be achieved without too much difficulty. If that is not eaten, then it becomes more challenging. For example, one would have to eat 2.5kg broccoli daily (1000mg day intake / 40mg per 100g = 25; 25 * 100g = 2.5kg).
Types of Supplements
The two main types of supplements are2:
- Calcium carbonate
- Calcium citrate
Other types are:
- Calcium acetate
- Calcium lactate
- Calcium gluconate
- Calcium citrate malate
- Tri-calcium phosphate
Maximal DosageThe maximum dosage of calcium from normal food and supplements together is according to the US Institute of Medicine1:
|Maximum Daily Dose (Upper Level - UL)|
|Children 1-18 years||2'500 mg|
|Adults 19-70 years||2'500 mg|
|Adults older than 70 years||2'500 mg|
Adults are bigger, but children require more calcium due to them growing. Because of that, the values are not lower for children.
The maximum dose has been chosen such that the risk of hypercalcemia and kidney insufficiency (milk-alkali-syndrome) remains low. There is insufficient data to also take into account the formation of kidney stones.
For calcium mainly the deficiency plays a role. If much milk products are consumed, then it should not be a problem to achieve the recommended daily intake. If not many or no milk products are eaten, then can become challenging, because quite a large amount of other food has to be eaten to achieve the desired calcium intake.
A too low calcium intake is over the longer term a risk factor for osteoporosis (bone fragility).