Calcium is one of the most important components of the human body and is found mainly in the skeleton and in the teeth, about 99%, while the remaining 1% is circulating in the blood. Bones and teeth are made up of strong and resistant tissues thanks to calcium but they also have a very precise function, they are in fact a reserve and a source of calcium for the organism that uses this precious element, once it has entered the blood flow, in different biological processes.
Calcium, properties and benefits of this important element
Calcium plays a key role in the health and functioning of the human body. In fact, this element participates in nerve transmission, vascular contraction and vasodilation, in the synthesis of hormones and in the sending of signals between cells (Dietary Reference Intakes for Calcium and Vitamin D, National Academies press, 2011). In addition to this, a proper calcium intake could be useful in case of polycystic ovary syndrome, or PCOS. Indeed, according to a study (Kia et al, Health Promot Perspect, 2015), it was found that women with PCOS had lower calcium levels than women without PCOS and that this deficiency was due to a low calcium diet. These results suggest that an improvement in polycystic ovary syndrome may occur with a varied diet that includes food sources of calcium. Finally, a correct calcium intake is also connected to a reduced risk of developing osteoporosis and incurring bone fractures. Indeed, it was observed that people who followed a vegan diet with a low calcium intake had a higher risk of bone fractures than the rest of the studied population, which included both vegetarians and people who ate fish and meat (Appleby et al, Eur J Clin Nutr, Dec 2007).
Calcium food sources and daily requirements
And how can an adequate supply of calcium be guaranteed? With the diet. Main sources of calcium are milk and dairy products such as yogurt and cheese, but also vegetables, cereals, legumes and some fish that are eaten with fishbone. For example, 100 grams of sardines provide about 320 mg of calcium, 250 ml of skimmed milk around 300 mg, just like 230 ml of yogurt. 60 grams of cooked turnip tops contain 100 mg of calcium, the same amount contained in about 120 grams of raw cabbage while 120 grams of raw Chinese cabbage bring about 70 mg (Bone Health and Osteoporosis: A Report of the Surgeon General, Office of the Surgeon General, 2004). There are also various calcium fortified foods, that is, that have calcium added to them, such as plant milks or fruit juices. According to the guidelines, the daily calcium requirement is 1000 mg in adults, 1200 mg in menopausal women and 1300 mg in children and teenagers between 4 and 18 years (NIH).
Calcium supplements, side effects and benefits
Another way to take calcium is through supplements that should always be prescribed by a doctor. Generally, a varied diet is sufficient to guarantee the right amount of calcium, however there are some conditions such as a vegan diet or a lactose intolerance that could benefit from calcium supplementation. In fact, in case of a deficiency of this mineral, the body takes calcium from bones that become excessively fragile. Calcium supplements are typically found in the form of calcium carbonate, which is less expensive but often the cause of gastric disorders, and calcium citrate. However, as anticipated, supplements should only be taken under medical supervision, avoid DIY as, although calcium is fundamental for different biological processes, even an excessive amount of it is harmful. Too high levels of calcium would be connected to an increased cardiovascular risk even if the basic mechanism has not yet been understood and not all researches are in agreement (Reid et al, Endocrinol Metab, 2017 - Shi et al, Endocrinol Metab, 2015). Finally, it should be emphasized that high levels of calcium are generally not reached with nutrition but are almost always caused by supplements.
Calcium and vitamin D
Finally, the availability of calcium is not only linked to diet but also to the presence of vitamin D, which regulates calcium metabolism and determines its absorption by the bones. A deficiency of vitamin D is reflected in a lack of calcium in the bones and consequently in the body. Therefore, a diet that includes calcium is not sufficient to guarantee correct levels of this mineral but the presence of vitamin D is also necessary (Beto, Clin Nutr Res, Jan 2015). The sun, taken with due precautions, is an excellent source of vitamin D. Food sources of vitamin D are, for example, salmon, red of eggs, some mushrooms and fortified foods, such as milk, in this case it is indicated on the label (Dietary Reference Intakes for Calcium and Vitamin D, National Academies press, 2011).