In the fifties, nutritionist Adelle Davis wrote in one of her books this poetic words about calcium: There are few nutrients which can increase the graciousness of a home as much as can calcium. Without it, tempers flare and irritabilities are constant. With it, serenity can at times prevail. The reason she wrote this is that one of the first symptoms of calcium suboptimal intake involves our nervous system.
We become restless, agitated, nervous, and have a hard time falling asleep. Give us some calcium, and we’ll calm down. As we shall see, however, the real consequences of a chronically suboptimal calcium intake are far more serious than simple restlessness and irritability.
Calcium is the most abundant mineral in ourbody, where it plays a fundamental structural role in our bones and teeth. Together with phosphorous, calcium forms hydroxyapatitecrystals that strengthen the protein matrix of our skeleton. Indeed, of the 12 hundred grams (1.2 kg) of calcium that the human body contains on average, 99% is found in our bones and teeth. The remaining 1% is found primarily in ourbloodstream and outside our cells, while the amount of calcium inside our cells is extremely limited and very strictly controlled.
This tiny amount of calcium, however, is extremely powerful and acts a little bit like dynamite: It is very powerful and can be very useful if used in a controlled way, but if it goes out of control, disasters result.
Calcium is necessary for muscle contraction, since it activates troponin in muscle cells. It is necessary for nerve impulses transmission (neurotransmission), since it allows release of neurotransmitters in the synaptic cleft. It is involved in blood clotting, as a co-factor of prothrombin. It is involved in blood pressure regulation, so much so that calcium deficiency is a risk factor for hypertension.
These are just a few of the many functions of calcium in our body. If we were to have no available calcium, our muscles could not contract and our nerves could not transmit signals: this conditionis called tetany, and can result in death. If on the other hand we were to have a large excess of calcium, this would also result in tetany and death. As you can see, calcium is no laughing matter.
It is not for nothing that calcium is the only mineral whose levels in our bloodstream are controlled not by one, not by two, but by three different hormones. To maintain blood calcium stable, these hormones can increase or decrease calcium absorption from food. Can increase or decrease calcium excretion via the kidneys, and can deposit or withdraw calcium from our bones. Indeed, calcium in our bones is in dynamic equilibrium with our blood.
If dietary calcium intake is chronically inadequate, these hormones can still maintain adequate blood levels of calcium by stealing it fromour bones, but our bones end up paying a very high price. By becoming depleted of calcium, they lose density and become more prone to fractures.
The three hormones involved in calcium homeostasis are parathyroid hormone (PTH), secreted by the parathyroid glands; calcitriol, which is the hormonally active form of vitamin D following activation in the kidneys; and calcitonin, produced by our thyroid. PTH is secreted when blood calcium drops, and in turn it tells the kidneys to activate vitamin D to calcitriol.
These two hormones will work to raise blood levels of calcium, by increasing its intestinal absorption, decreasing its urinary excretion, and taking some from our bones if necessary. In contrast, calcitonin is secreted when bloodcalcium raises, and it does the exact opposite. It will lower blood calcium by increasingits excretion and by promoting its deposition into our bones.
How much calcium do we need? The adult RDA for calcium is set at 1 gram. For women after 50 years of age, and for men after 70, the RDA is 1.2 grams.Calcium absorption from food is on average 25%, but can go as high as 60% if the body needs more. It is better absorbed in an acidic environment, for example with the stomach secretions during a meal, or with citric acid from lemon juice.
However, calcium absorption decreases with age, which is part of the reason why the recommended daily allowance for older adults is a little bit higher. A few dietary factors can decrease absorptionor increase excretion of calcium. Sudden increases in dietary fiber, phytate from whole grains, oxalate from some vegetables, and tannins from tea, red wine or chocolate will decrease calcium absorption. In contrast, if such substances form regular part of our diet, our body is able to adjust calcium absorption accordingly.
Other dietary factors can interfere with calcium, this time by increasing its excretion. The two major risk factors are high protein diets and high salt diets, in particular if consumption of fruits and vegetables is low. Catabolism of excess protein and chloride from salt, both create acids that need to be quickly buffered to maintain stable the pH of our bloodstream. The kidneys normally take care of that, but when their homeostatic ability is exceeded, calcium is stolen from our bones to buffer these acids and is subsequently excreted with the urines.
This is also very likely the reason why very high consumption of milk and dairy is associated not with a decrease, but with an increase in bone fractures. To a minor extent, caffeine abuse also leads to increased calcium excretion. As everybody knows, yogurt, milk and cheese are good sources of calcium, as long as they are not consumed in excessive amounts.
But there are equally as good calcium sources among plant foods. Most green leafy vegetables are excellent sources of calcium, among these bok choy (chinese cabbage), broccoli, kale, collard, turnipgreens, mustard green, brussels sprouts, cauliflower, head cabbage, kolhrabi, rutabaga and watercress. Calcium from all these vegetables is verywell absorbed, between 50% and 60%. Actually, it is absorbed more efficiently than calcium from dairy products, whose absorption is at about 30%. There are other vegetables, however, that although rich in calcium are not good sources of it, because absorption is limited by the presence of oxalates. For example spinach, rhubarb and swiss chardhave a lot of calcium, but absorption is lower than 5%. Chocolate is also a source of oxalate, so think twice before drinking chocolate flavored milk: you are not only getting an awful lot of added sugar, but you are also hindering calcium absorption. Nori seaweed, the one used for sushi, is a good source of calcium.
Whole grains can also significantly contributeto our calcium requirements, as well as almonds, beans and sesame seeds. Fish eaten with bones is a good source of calcium, think for examples small fish like sardines. Some waters are rich in calcium. Firm tofu has a lot of calcium because calciumcarbonate is used to make it. Finally, an increasing number of foods are fortified with calcium, for example some orange juices, soy milk and breakfast cereals. If foods are fortified with calcium, of course, this will be clearly stated on the food label.
Calcium also has a tolerable upper level, which is set at 2.5 grams per day for adults. If adequate calcium is undoubtedly important, excess calcium is also not a good thing. As soon as calcium starts being in excess, the first consequence is reduced vitamin D activation. Like we said before, the primary function of active vitamin D is to increase calcium absorption, so it makes perfect sense that if calcium intake is high, less vitamin D will be activated, since we don’t need to increase ca absorption. It is already high and this would be perfectly fine if the onlyfunction of vitamin D was to increase calcium absorption. But as it turns out, active vitamin D does a lot of other very important things that are potentially very very beneficial for ourhealth, it regulates expression of more than 40 genes, and may play important roles inpreventing a variety of diseases, as you already know.
if we over do it with calcium supplements, we suppress vitamin D activation and we end up missing on these secondary health-promoting effects of active vitamin D that are potentially very important. At higher intakes, calcium will then interfere with absorption of other minerals, such as zinc and iron. At even higher intakes, it will increase risk of kidney stones, and lead to calcification of soft tissues. Like we said before, acute calcium toxicity results in tetany and death. If you like my article subscribe for more information like this.
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