Calcium is the most abundant among the minerals in the body. The total content of calcium in an adult man is about 1 to 1.5 kg. As much as 99% of it is present in the bones and teeth. A small fraction of the calcium, found outside the skeletal tissue, performs a wide variety of function. Most of the blood Ca is present in the plasma since the blood cells contain very little of it. The normal concentration of plasma or serum Ca is 9-11 mg/dl. The hormones calcitriol, parathyroid hormone and calcitonin are the major factors that regulate the plasma calcium within a narrow range
What are the functions of Calcium in the body?
- Development of bones and teeth:- calcium along with phosphate, is required for the formation of hydroxyapatite and physical strength of skeletal tissue. Bones which are in a dynamic state serve as reservoir of Ca. Osteoblasts are responsible for bone formation while osteoclasts result in demineralization.
- Muscle contraction:– calcium interacts with troponin C to trigger muscle contraction. Calcium also activates ATPase, increases the interaction between actin and myosin
- Blood coagulation:– several reactions in the cascade of blood clotting process are dependent on calcium
- Nerve transmission:– calcium is necessary for the transmission of nerve impulse
- Membrane integrity and permeability:– calcium influences the membrane structure and transport of water and several ions across it.
- Activation of enzymes:– calcium is needed for the direct activation of enzymes such as lipase, ATPase and succinate dehydrogenase
- Calcium as intracellular messenger:– certain hormones exert their action through the mediation of calcium
- Release of hormones:– the release of certain hormones insulin, PTH, calcitonin from the endocrine glands is facilitated by calcium
What is the daily Recommended Dietary Allowance of calcium?
|0–6 months*||200 mg||200 mg|
|7–12 months*||260 mg||260 mg|
|1–3 years||700 mg||700 mg|
|4–8 years||1,000 mg||1,000 mg|
|9–13 years||1,300 mg||1,300 mg|
|14–18 years||1,300 mg||1,300 mg||1,300 mg||1,300 mg|
|19–50 years||1,000 mg||1,000 mg||1,000 mg||1,000 mg|
|51–70 years||1,000 mg||1,200 mg|
|71+ years||1,200 mg||1,200 mg|
What are the food sources of calcium?
Calcium rich foods are
- Cheese, Milk, yogurt
- Green leafy vegetables such as spinach, kale, turnips, and collard greens
- Fortified cereals
- Fortified orange juice
- Soy beans
- Fortified soy milk
- Fish, egg yolk
the absorption of calcium mostly occurs in the duodenum by an energy dependent active process. It is influenced by several factors
Factors promoting Ca absorption
- Vitamin D induces the synthesis of calcium binding protein in the intestinal epithelial cells and promotes Ca absorption.
- Parathyroid hormone enhances Ca absorption through the increased synthesis of calcitriol
- Acidity is more favourable for Ca absorption
- Lactose promotes calcium uptake by intestinal cellos
- The amino acids lysine and arginine facilitate Ca absorption
Factors inhibiting Ca absorption:-
- High content of dietary phosphate results in the formation of insoluble calcium phosphate and prevents calcium uptake
- The free fatty acids react with Ca to form insoluble calcium soaps. This is particularly observed when the fat absorption is impaired
- Alkaline condition is unfavourable for Ca absorption
- High content of dietary fiber interferes with Ca absorption
- Phytates and oxalates interfere with Ca absorption
What are the diseases associated with calcium?
Hypocalcemia:- is a more serious and life threatening condition. It is characterized by a fall in the serum Ca to below 7 mg/dl, causing tetany. The symptoms of tetany include neuromuscular irritability, spasms and convulsions. Hypothyroidism is associated with a decrease in serum Ca and an increase in serum phosphate, besides the reduced urinary excretion of both Ca and phosphrous
Hypercalcemia:- the serum cxalcium level is increased in hypercalcemia. It is associated with hyperparathyroidism caused by increased activity of parathyroid glands. Decrease in serum phosphate is noticed in this condition.
Rickets:- rickets is a disorder of defective calcification of bones. This may be due to a low levels of vitamin D in the body due to a dietary deficiency of Ca and P or both. The concentration of serum Ca and P may be low or normal.
Osteoporosis:- it is characterized by demineralization of bone resulting in the progressive loss of bone mass. The elderly people of both sexes are at risk for osteoporosis. However, it is most predominantloy occurs in the postmenopausal women. Osteoporosis results in frequent bone fractures which are a major cause of disability among the elderly. So higher dietary intake of Ca is recommended for elderly people.
What are the risks of taking calcium?
Side effects:- At normal doses, calcium supplements may cause bloating, gas, and constipation. Very high doses of calcium can cause kidney stones. Research has found an increased risk of heart attacks and strokes in some people taking calcium supplements in addition to a diet high in calcium, though the true accuracy of these findings is being actively debated by experts.
Interactions:-If you take any prescription or over-the-counter medicines regularly, ask your doctor if it’s safe to use calcium supplements. Calcium can interact with drugs for heart disease, diabetes, epilepsy, and other conditions. Excessive doses of vitamin D can result in dangerously high levels of calcium. High doses of calcium can also interfere with the absorption of other minerals, like iron and zinc. In general, take calcium one to two hours apart from other supplements or medications. When taken at the same time, calcium can bind those products and pass them unabsorbed from the body.
Risks:- People with kidney disease, heart problems, sarcoidosis, or bone tumors should not take calcium supplements unless their doctors suggest it.
Overdose:- Excessive levels of calcium in the blood can cause nausea, dry mouth, abdominal pain, irregular heartbeat, confusion, and even death.