Calcium: Its importance, food, absorption and side effects

What is calcium?

It is important to consume calcium-rich foods as part of your balanced diet.

Calcium is the main component of bones with the largest percentage (up to 99%) being found within the bones in the form of hydroxyapatite, while the rest of the calcium is in the bloodstream in a water-soluble form and contributes to cell signaling. [1]

What are the properties of calcium?

Calcium, in addition to being an element of our skeleton, has important properties and participates in many biochemical processes of the body. For example, it helps muscle proteins perform the work of contraction. When a nerve stimulates a muscle, the muscle cell “opens” channels and releases calcium. When calcium moves out of the muscle cell, the muscle relaxes.

The role of calcium in muscle function also includes maintaining the action of the heart muscle. Calcium relaxes the smooth muscle that surrounds blood vessels and this helps regulate blood pressure.

The metal plays a key role in blood clotting, a complex process that has many steps involving various substances. It is also a cofactor for many enzymes (mainly digestive) which cannot function effectively without it.

In particular, calcium contributes to normal blood clotting, normal energy-giving metabolism, normal muscle function, normal neurotransmission, the proper functioning of digestive enzymes, it has a role in the process of cell division and specialization. Finally, it is required to maintain the normal composition of bones and teeth.

How much calcium do I need?

The Recommended Daily Intake depends on many factors. Based on age we have the following doses: [1]

The above amounts of calcium are the recommended intake from the diet and not what the body absorbs. When you get 1 gram of calcium in the diet, the net absorption is about 300 mg (30%). This is the amount of calcium the body actually needs, however absorption can vary considerably between foods.

Who needs more calcium?

Calcium needs depend on several factors such as: [1]

• the age,
• pregnancy or stage of pregnancy,
• breastfeeding
• and hormonal status.

Children and teenagers

Children and teenagers have a greater need for calcium than adults (most of the time). Calcium is essential in children’s nutrition, as it plays an important role in bone development and protects against the onset of osteoporosis in adulthood. [2]

Studies show that young children and babies who do not get adequate amounts of calcium and vitamin D are at increased risk of developing rickets.

It is also important to get calcium from other food groups such as: green leafy vegetables, fish, tofu and calcium-fortified foods.

Postmenopausal women

It is worth noting that after menopause, women usually need calcium with vitamin D to keep their bones healthy and avoid the decrease in bone density that often leads to osteoporosis. [2]

They need plenty of calcium and in most cases when the calcium in their food does not cover them, they have to take supplemental calcium in the form of tablets. The doses most often recommended by experts are 1000 mg of Calcium with 400-800 IU of Vitamin D per day. [2]

Pregnancy

Based on studies, calcium supplementation in pregnant women who did not get enough from their diet was shown to reduce the risk of pre-eclampsia and gestational hypertension when used in doses of 1g/day. [2][9][10]

At the same time, studies support the protective role of calcium in the cardiovascular system of the fetus that continues into childhood, while they observed that women who used calcium minimized the chances of premature birth and complications during the 2nd half of pregnancy. [2]

During pregnancy and breastfeeding women need 1,300 mg at age 14-18 years old and 1,000 mg at other ages.

Other categories

People who may not be getting enough calcium from their diet are: [8]

• Vegetarians who avoid milk and dairy products
• People with lactose intolerance
• People with eating disorders
• People with irritable bowel syndrome and inflammatory bowel disease
• People receiving cortisone medication
• Women who exercise excessively, where they end up with menstrual disorders

These people may need to take calcium supplements regularly.

What are the forms of calcium?

Calcium, in its natural form, does not exist as a free element but only in compounds with other components (salts). These salts are mainly: [5]

• Calcium Carbonate (40% elemental calcium)
• Calcium Citrate (21% elemental calcium)
• Calcium Gluconate (9% elemental calcium)
• Calcium Lactate (13% elemental calcium)

The two main forms of calcium supplements are carbonate and citrate.

Calcium Carbonate: This type is the most available and the most economic. It contains 40% elemental calcium which is a significant amount. If a pill has 500 mg of calcium carbonate, then it has 200 mg of elemental calcium. Calcium carbonate requires stomach acid in order to be absorbed, so these supplements should be taken with meals. However, this form is more likely to cause side effects such as gas, bloating and constipation.

Calcium Citrate: Contains 21% elemental calcium which means you will need to take more pills. Its advantage is that it is not dependent on gastric acid, so it can be taken at any time, with or without food. It is useful for people who suffer from inflammatory bowel disease or whose stomach does not produce much acid. If you are taking medications that block stomach acids (H2 blockers or proton pump inhibitors), then calcium citrate is your choice.

Another form of calcium in supplements includes calcium phosphate.

Foods rich in calcium

Dairy products are a good source of calcium. One serving is equivalent to a glass of milk (250 ml), a cup of yogurt (200 g) or a slice of cheese (40 g). Hard cheeses, such as Parmesan, have a higher concentration of calcium than softer varieties. Small fish (sardines, atherina) eaten with their bones are also rich

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Fruits rich in calcium are figs, raisins, apricots, orange (as well as orange juice), berries, qiwi, pineapple and papaya. Bananas do not contain much calcium, but they are rich in FOS, that improve gut microbioma and so calcium absorption.

What affects calcium absorption?

However, calcium bioavailability (absorption by the body) must be taken into account. There are a number of factors that can affect bioavailability. [3]

• Phytic and oxalic acid. Phytic acid is found in the bran of cereals and binds calcium and other minerals, making them insoluble and therefore unabsorbable from the gut. If you eat a lot of bread and other whole grains you will need more calcium from your diet. Oxalic acid is a more potent inhibitor of calcium absorption than phytic acid. Found in cocoa, spinach, soy. In the case of calcium, it prevents intestinal absorption because it forms calcium oxalate. Less than 5% of the calcium in spinach is absorbed by the body. Also, a study showed that if you consume spinach and milk at the same time, the absorption of calcium from the milk is reduced. From broccoli, which has little oxalate, more than 50% of calcium is absorbed.
• Vitamin D deficiency. Vitamin D is critical for calcium absorption. It is produced in the body due to exposure to UV radiation but is also found in fatty fish and in small amounts in eggs. [7]
• Caffeine. The caffeine in coffee and tea acts as a mild diuretic and the calcium is excreted before the body can use it. Consuming these drinks in small quantities, a couple of cups a day, is relatively harmless as 240 ml of coffee leads to the urine about 4 mg of calcium.
• Salt. Sodium intake causes an increase in urinary calcium excretion. An increase of 2.3 g. of sodium in the diet leads to 40 mg of calcium in the urine. This is a large amount. Over a period of 20 years, assuming the body has 1 kg of calcium, this equates to a 15% loss of bone mass.
• Proteins. Increased protein intake helps calcium absorption but at the same time causes increased urinary excretion. A few years ago, it was believed that eating too much protein contributed to osteoporosis because it caused calcium to be excreted in the urine. Newer research has shown that proteins stimulate the release of acid in the stomach, which, in turn, enhances calcium absorption. Proteins are probably neutral in their role in osteoporosis. They may even play a positive role as a part of the bones consists of protein (minerals make up 60% and water 10%). [4]
• Alcohol. Drinking alcohol can affect calcium status by reducing calcium absorption and inhibiting enzymes in the liver that help convert vitamin D into its active form. However, what amount of alcohol is required to affect calcium status is unknown.
• Magnesium. This mineral plays a role in building strong bones. It is needed for the secretion of parathyroid hormone which increases the absorption of calcium. [7]
• Smoking. Studies show reduced bone mass among smokers. The reason is not well understood but it may be that smoking interferes with the absorption of calcium from the intestine.
• Diseases. For example, celiac disease in which the absorption of fat-soluble vitamins and minerals is affected. Also, if you don’t have good kidney function, calcium deficiency can occur through increased urinary loss.

 What does calcium deficiency cause?

According to the latest statistics from the UK government’s National Nutrition Survey, 5% of men and 8% of women are deficient in calcium and 14% of teenagers do not get enough. The most common symptoms that indicate a lack of this metal are:

• Frequent injuries: Low calcium levels result in weakened bones and therefore frequent injuries.
• Frequent cramps: Chronic lack of calcium leads to dysfunction of the muscular system. We must not ignore that it is a very important electrolyte.
• Hypertension: Rarely, the cause behind high blood pressure is a low concentration of calcium in the body.
• Neurological symptoms: In some cases of lack of the metal, there is intense irritability and numbness in the fingertips. In extreme cases hallucinations and confusion occur.[6]
• Brittle nails
• “Easy” bleeding: For example, frequent nosebleeds.

Chronic calcium deficiency can lead to rickets (bones become soft and pliable and misshapen), osteoporosis (bones wear out, become porous and spongy) and osteopenia, as well as disturbances in metabolic rate and the normal functioning of other bodily processes. [6]

Contraindications-Interactions

People with hypothyroidism who are on medication should avoid taking calcium supplements, as absorption may be affected its absorption.

In addition, fluoride as well as zinc is recommended to be taken at a distance from food supplements containing calcium, as the absorption of the latter may be reduced. Finally, calcium supplements should be taken away from iron preparations. [7]

Calcium: Side effects

Increased calcium intake may lead to undesirable effects. As with any other minerals or vitamins it is important to get the right amount.

Sometimes blood calcium levels can become too high, leading to hypercalcemia characterized by stomach pain, nausea, irritability, and other symptoms. This condition can be caused by many conditions, including dehydration, thyroid disease and malignancy. However, the use of high-dose calcium or vitamin D supplementation increases the risk, especially in postmenopausal women. [11]

Calcium supplements are usually well tolerated but some people may experience bloating or constipation (a more common side effect of calcium carbonate). If this happens, contact your doctor. [7]

To avoid constipation eat more fiber (from fruits, vegetables and whole grains), drink six to eight glasses of water a day and be physically active.

Rarely, calcium supplements can cause kidney stones in predisposed individuals. The risk, however, is considered very small and begins when the intake is above 3,000 mg per day.

High calcium intake from either dairy products or supplements has been associated with increased risk for prostate problems and cardiovascular events in some, but not all, observational and interventional studies. There is currently no evidence of such harmful effects when people consume 1,000-1,200 mg of calcium per day (diet and supplements combined). [1]

The use of calcium supplements at levels of 500-600 mg per day is considered safe but you should only take the supplements as directed and after consulting your doctor.

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References

1. Calcium Intake and Health
2. The good, the bad, and the ugly of calcium supplementation: a review of calcium intake on human health
3. Caffeine, urinary calcium, calcium metabolism and bone
4. The impact of dietary protein on calcium absorption and kinetic measures of bone turnover in women
5. Calcium supplementation in clinical practice: a review of forms, doses, and indications
6. Calcium Deficiency Causes
7. All About Calcium Supplements 
8. Calcium and calcium supplements: Achieving the right balance
9. Calcium supplementation during pregnancy for preventing hypertensive disorders and related problems
10. Risk factors for pre-eclampsia at antenatal booking: systematic review of controlled studies
11. Calcium revisited: part II calcium supplements and their effects
12. calcium citrate