If you have heard of Medicine Direct, then you know about their calcium products. The most abundant cation in our body system is calcium. This mineral is essential for the preservation of neuromuscular function. It makes up 2 percent of our entire body weight and 26 percent of our teeth and bones dry weight, as carbonates and phosphates. Every day, there is an exchange of bone calcium with about 0.5g of serum calcium.
The factors that determine how calcium is absorbed are listed below:
The body requirement of a normal person is 30% of calcium but is more in a deficient person. A higher calcium concentration in the food means a higher absorption. Intestinal rush e.g. diarrhoea reduces calcium absorption of calcium. Reduced fat absorption also diminishes calcium absorption. Amino acids and milk sugar (lactose) improve calcium absorption. Vitamin D is an essential factor in stimulating calcium absorption. The proportion of calcium to phosphorus in food has a significant effect on absorption.
Calcium is absent in red blood cells but present in plasma. The level of the serum is 2.4mmol/l, in which half is protein bound and the other half ionized. Ionized calcium can be diffused. The parathyroid glands maintain its usual level of serum. Alkalosis can decrease the serum calcium level that can be ionized. Reduction of ionic calcium results in higher muscle tetany and irritability. The remaining serum calcium is protein bound, mostly albumin. Hence, when the plasma albumin drops the serum calcium level is low. However, tetany does not develop because the drop is in the non-diffusible form.
Parathyroid hormone (PTH) from the bones assembles phosphorus and calcium to preserve blood level. Hyperparathyroidism causes minerals to be reabsorbed. PTH also rouses the kidney mitochondria to raise calcidiol to calcitriol conversion, which improves calcium absorption in the intestine. C cells of the thyroid gland produce a peptide hormone called Calcitonin. It has a short life and is secreted always. As the serum calcium rises, the secretion rises. It helps to preserve blood level by inhibiting the release of calcium from the bones and boosting urinary excretion. In therapeutics, calcitonin is used for high serum calcium level. Estrogen increases calcitonin level and inhibits bone loss. Loss of bone post menopause is attributed to estrogen decrease.
99 percent of the calcium in the body is stored in the teeth and bones. The bones are the reservoir where calcium is always stored and reabsorbed. This activity happens more in the young and drops with age. About one percent of the entire calcium in the body circulates and is in soft tissue. During puberty, under the stimulus of sex hormones, girls and boys amass calcium of nearly 200 mg, and 400 mg, respectively, a day. Positive calcium balance takes place only when the calcium intake is more than 1000 mg per day.
Nearly half of calcium taken daily is not absorbed and goes out in the faeces. Vitamin D taken in high dose can reduce the calcium content in the faeces. It can also be passed out through the urine. The usual range of urinary calcium in adults on a standard diet is 100-300 mg and100-250 mg for men and women respectively. The proper functioning of the kidney will excrete nearly 8% of filtered calcium. Diets high in protein reduce calcium reabsorption by the kidney and increases excretion of urinary calcium.
Calcium and phosphorus are essential for the formation of the bones. Bones contain a protein matrix that has calcium phosphate stored in it. For this matrix to be formed there is the need for sex hormones, vitamins A and C, and proteins. The calcium deposited in the bones is constantly turned over with the one in the blood and other tissues at a 0.5g daily rate. Ionic calcium influences neuromuscular impulsiveness of the controlled and uncontrolled muscles. If the ionic serum calcium concentration is reduced, neuromuscular impulsiveness is significantly raised, as in tetany. Calcium is also needed for blood clotting and preservation of tube permeability.
Milk and products from milk are good calcium sources. Fatty products such as ghee, cream and butter, have low calcium but enough vitamin D that aids the absorption of calcium. Calcium is found in molasses and vegetables like cauliflowers, potatoes, pulses and peas. The calcium content of a pumpkin leaf is about 240300 mg. When betel leaves are chewed with lime, dietary calcium is augmented. Calcium is also found in hard water. Chewing fishbone is another good source of calcium. The most affordable commercial source of calcium is calcium carbonate.
The daily dose required for calcium intake depends on a lot of factors favourable or unfavourable to its absorption. In the tropical zone, with sunlight exposure, a good calcium balance can be sustained even if the intake is lower than normally recommended. With athletes undergoing physical activity, the requirement is higher. The requirement is also higher for pregnant women and American girls in puberty stage. To make room for losses and everyday needs, a lactating mother needs 1.2 g of calcium every day. Children that are breastfeeding need 50 mg calcium per kg of their daily body weight.
The following situations can lead to deficiencies:
Hypoparathyroidism and pseudohypoparathyroidism. Deficiency in Vitamin D due to non-exposure to sunlight, bad diet and reduced absorption in steatorrhea. Hypoproteinemia (Low serum proteins).
Ingestion of viomycin, fluoride and sodium. After Hypothermia for cardiac surgery. Certain cases of hypocalcemia following gastric surgery maybe because of hypoproteinemia. A high-protein diet, increasing urinary calcium secretion. Rheumatoid arthritis.