Calcium is an important mineral that is necessary to maintain our health. Adequate calcium intake is necessary for the prevention and treatment of osteoporosis, which becomes a serious global health problem. However, only few people realize that high or inappropriate doses of calcium supplements can cause side effects and health concerns. That is why calcium supplementation should be used with caution and always take into account risks and benefits of each individual. In this article, we take a closer look at what the potential health risks of calcium supplementation can be.
Article at a glanc:
- Calcium metabolism in human body
- Calcium sources and recommended intake
- Interaction of calcium with other substances
- How to recognize calcium deficiency?
- Calcium excess
- Risks of calcium supplementation
- Calcium and cardiovascular disease
- Calcium and kidney stones
- Calcium and osteoporosis
Calcium metabolism in human body
Calcium is the most abundant mineral element in the human body. Almost 99% of calcium is found in our bones and teeth, where it occurs together with phosphorus in the form of hydroxyapatite. Calcium plays a key role in maintaining healthy bones, but it is also involved in other biological functions in our body. It is needed for proper blood clotting, muscle contraction, transmission of nerve impulses, regulation of hormone production and secretion of certain enzymes.
It is therefore necessary to maintain a balanced level of calcium in the blood. This is regulated by parathormone from parathyroid glands and calcitonin produced by thyroid gland. If the levels of calcium in the bloodstream are high, calcitonin will promote its incorporation into the bones and increase its excretion by the kidneys. On the contrary, if the level of calcium in the blood drops below the desired level, parathyroid hormone will support the resorption of calcium by the kidneys, with the help of vitamin D it will increase the absorption of calcium from the intestines and at the same time cause the release of calcium from the bones. Bones therefore represent a calcium reservoir in our body. But if the calcium intake is low over a long period of time, too much calcium is removed from our skeleton and the bones become more fragile, weak and thin, which may lead to osteoporosis.
Calcium sources and recommended intake
Calcium is one of the essential substances, which means that our body cannot synthesize calcium and we are dependent on its intake from the diet. Foods rich in calcium include mainly dairy products, sardines, anchovies, nuts, seeds (especially almonds and sesame seeds), some vegetables such as cabbage or broccoli, and green leafy vegetables in general.
According to the European Food Safety Authority (EFSA), the recommended daily intake for an adult is 1000 mg of calcium. For children from 11 years of age, requirements for calcium intake slightly increase to 1150 mg per day. This is related to the period of growth and building of bone tissue.
Interaction of calcium with other substances
Calcium easily binds to certain substances such as phytates and oxalates and forms insoluble compounds with them, which reduces its absorption.
Magnesium is an element that works closely with calcium in regulation of nerve impulses and muscle contractions. The recommended intake ratio of these two minerals should be 2:1 in favor of calcium. When supplementing calcium alone, the balance between calcium and magnesium can be disrupted and can lead to possible health complications.
Calcium balance in our body is also influenced by sodium. High sodium intake increases calcium excretion in urine and sweat. That's why high salt intake leads to increased calcium losses.
In the elderly population, calcium deficiency is multifactorial. Overall, it is caused by a reduction of dietary energy intake (including calcium sources), lower calcium absorption from the small intestine due to low vitamin D levels and also by reduced calcium retention by the kidneys.
In general, we can increase calcium absorption from the diet by an adequate amount of vitamin D, the presence of vitamin C, a sufficiently acidic environment in the small intestine or by physical activities.
On the contrary, inappropriate pH of the small intestine, presence of antinutrients in the diet, vitamin D deficiency and also high intakes of refined sugar, salt, coffee, alcohol, smoking or lack of exercise and aging reduce the level of calcium in the body.
We covered the topic of mineral absorption and antinutrients in food in more detail in the article entitled "The absorption of mineral substances in the human body and what can we do to improve it?”
How to recognize calcium deficiency?
Calcium deficiency, or hypocalcemia, can manifest itself in the form of muscle cramps, muscle twitches, nervous sensitivity, insomnia, fatigue, dry skin, brittle nails or dental problems such as irritated gums, brittle teeth or dental caries. In the long term, calcium deficiency can lead to osteopenia (=reduction of bone mineral density), which can lead to the development of osteoporosis (=thinning of bones and their susceptibility to fractures).
Groups at risk of calcium deficiency include people who eliminate dairy products from their diet, people with lactose intolerance or allergies to cow's milk proteins and vegans. However, calcium deficiency doesn´t have to be caused by a lack of calcium in the diet, but rather by health problems such as kidney and intestinal diseases or by the use of certain drugs such as diuretics.
Excess of calcium, or hypercalcemia, is not very common. The absorption of calcium is limited and the body excretes calcium excess through the kidneys. The upper tolerable limit of calcium intake is 2500 mg per day and the intake of this amount is considered safe.
The cause of hypercalcemia can be caused by diseases such as chronic kidney failure, hyperparathyroidism or oncological diseases. Symptoms of calcium excess include constipation, excessive thirst, frequent urination, muscle weakness, fatigue, exhaustion, cardiac arrhythmias and palpitations.
Risks of calcium supplementation
Although calcium supplementation makes sense in justified cases and brings health benefits, it is also necessary to take into account possible risks. Excessive calcium supplementation is often connected to digestive tract issues like constipation, bloating and flatulence.
Regarding health risks, calcium is most often associated with cardiovascular diseases or kidney stones.
Calcium and cardiovascular disease
One of the most discussed risks of calcium intake is cardiovascular health. Some studies  have confirmed that the use of calcium, especially without the simultaneous supplementation of vitamin D, increases the risk of heart-attack by up to 30%. Another study , conducted on 1,471 healthy postmenopausal women, points to the fact that calcium supplementation higher than 1000 mg/day increases the incidence of cardiac events.
It is remarkable that dietary calcium intake does not have the same effect on cardiovascular health compared to calcium supplements. A study  comparing dietary calcium intake with calcium supplementation showed that the risk of heart-attack increased significantly only with calcium supplementation. It is not that surprising that calcium supplementation increases the risk of cardiovascular diseases. Taking calcium increases its serum levels, which contributes to the probability of vascular calcification. The calcification of blood vessels is one of the factors by which doctors assess the risk of a heart-attack.
Calcium and kidney stones
Kidney stones belong among urinary system diseases. They are hard objects that form inside your kidney when urine is oversaturated with stone-forming substances such as calcium, oxalates or uric acid. The main component of kidney stones is calcium and it occurs mainly in the form of calcium oxalate or calcium phosphate.
Some studies show   that the use of calcium supplements increases the risk of kidney stones, while the intake of calcium from the diet can reduce the risk. This can be explained by the fact that eating food rich in oxalates together with calcium rich food binds these substances to each other already in the digestive tract, which can prevent the formation of stones in kidneys. Taking into account the possible risks of cardiovascular diseases and kidney stones development, it is more beneficial to take calcium from the diet.
Calcium and osteoporosis
As we explained in the previous article dedicated to osteoporosis, the most important period in the prevention of this disease is the period of growth and adolescence. According to the National Osteoporosis Foundation (NOF), calcium intake and physical activity have the biggest impact during this period, when bone mass is formed. There are a large number of studies showing that dietary calcium intake or calcium supplementation has a positive effect on bone health by people of different ages, genders and ethnicities.
Regarding osteoporosis and bone health, it should be emphasized that it is not just about getting enough calcium, but about overall lifestyle and nutrition. Other nutrients needed for building strong and healthy bones include for example protein, vitamin D3, vitamin K2 and magnesium. Last but not least physical activity and adequate weight-bearing exercises have beneficial effects on bone health for people of all ages. By children and adolescents, it stimulates the increase of bone minerals, while by adults its primary goal is to maintain bone mass.
To conclude, although calcium supplements are beneficial in the treatment of certain health complications, they should be used with caution with regards to the possible risks.
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