Did you know that a person has about one kilogram of calcium in the body? Yes, it’s true but the calcium is mostly found in the bones and very little in the blood. Besides being needed for bone growth calcium is also needed for functions like neuromuscular excitation, blood coagulation, and membrane permeability. The good thing is that the calcium present in the bones helps to maintain the calcium level in blood even if there is the dietary deficiency. Blood calcium level is also maintained through the interaction of Vitamin D with various hormones in the body. Perhaps you might not know that a lot of calcium is lost through urine, stools, bile, and sweat which could be as much as 700mg per day. Therefore the body needs calcium to make up for this loss and additionally, calcium is required during child’s growth and by mothers during lactation. The requirement for calcium and phosphorus are taken together because the requirement of phosphorus depends on the intake of calcium.
Dietary intake of calcium
In India, in some communities, milk intake is low and so most dietary calcium is obtained from cereals which keep intakes low at 300 to 600mg per day. In communities where the intake of milk is high calcium from the diet easily reaches an intake of1000mg per day. However, even in communities that have a low intake, the calcium balance is maintained as the body adapts to those levels. According to some studies it has been estimated that reducing animal protein from 60g to 20g or sodium from 150 to 50m mol/d could decrease calcium requirement by about 200mg/d and a combination of both could reduce requirement by 400mg/d.
In India, calcium requirement is determined by
- Calcium balance studies on subjects consuming variable amounts of calcium
- A factorial model using calcium accretion based on bone mineral accretion data obtained isotopically or by scanning,
- Clinical trials investigating the response of the change in calcium balance or bone mineral content/density or fracture rate to varying calcium intakes.
- With the advent of DXA measurements bone health can be measured at multiple points and an ICMR study has generated the large database on bone health of Indian population using DXA and some of the aspects of the study have been considered by ICMR for determining calcium requirement.
The adult requirement of calcium
Calcium is required because it is important to attain peak bone density so as to prevent osteoporotic fractures in later life. During puberty, calcium helps to optimize growth rate of bone mass for correct body size and skeletal maturity. Women are at a greater risk of developing bone abnormalities due to poor nutrition and so need correct calcium dosage. The earlier dosage of calcium was 400 mg per day but this was not able to protect bone health and some segments of the population had osteoporosis as a result. The ICMR Expert Committee is of the view that adults require 600 mg/d of calcium. In India, it is seen that with lower incomes, calcium intake in the diet also decreases which results in more chances of osteoporosis as compared to people in the same age group but with higher incomes.
Calcium requirement for children
A number of calcium balance studies are available which recommend various calcium intake requirements for children. However, to obtain a retention value of 200mg calcium, the dietary intake is expected to be 600mg. In children loss through waste is estimated to be around 100mg which is about 3 to 4mg per kg of body weight. If the factorial approach is used the requirement will be 253 mg keeping in mind faecal waste (50) + urine (48) + sweat (30) +retention (125) = 253 mg. For 253 mg to be retained at a rate of 40% absorption, the dietary calcium needed is 600 mg.
The adolescent requirement of calcium
According to studies it is found that between 12-14 years of age total adult bone mineral content of about 20% is already formed. Since there is no calcium balance data for adolescent boys and girls in India, calcium intake for this age group has therefore been based on American boys and girls. Adding loss through waste as well as calcium absorption rate as 60%, the need of dietary calcium has been worked out to about 487-701 mg/d for boys and 300-550 for girls in the age group of 11-16 years. An intake of 921 mg/d in the total group works out to about 980 mg of calcium per day in the pubertal group of over 10 years of age.
Women in this age group have an increase of urinary calcium of about 30mg daily. Besides this, they also have low absorption of calcium and bone resorption also requires more calcium. A study by Teotia and Teotia concludes that women with higher intake of calcium entered osteoporotic and fracture zones of bone density 10 years later than those with lower intake. In addition, women with hard work and those with lifetime vegetarian habit are stated to be at reduced risk of osteoporosis.
Studies on the 3 socioeconomic groups at NIN show that even after the age of 50 years, the extent of osteoporosis in the spine is only 16% in the HIG group as compared 65% in the LIG group with 65%. So women in this category require an additional 200 mg/d of calcium.
The Committee also considered alongside the desirable intake of phosphorus (P). Since P deficiency is unlikely to occur on the types of diets consumed in India, ensuring an adequate P intake may not present a problem. ICMR Committee suggests that an elemental Calcium: Phosphorus ratio can be maintained at 1:1 in most age groups, except in infancy, where the ratio suggested is 1:1.5.
Recommended intakes of calcium and phosphorous (mg/d)
|Children||1 – 9 years||600||600|
|10 – 18 years||800||800|
To achieve this level of intake, a minimum of 200 ml of milk/d would be essential on a cereal-legume diet.
NOTE: The guidelines and recommendations in the article and the table above are as per Indian Council of Medical Research (ICMR) criteria.