Type of Papers: Reports completed by expert consultations and published by the World Health Organization jointly with the Food and Agriculture Organization of the United Nations (FAO).
Note: Two WHO reports were summarized together as they contain much of the same information. See references below.
- Calcium is required for bone mineralization (bone formation), maintaining strength in the skeleton and supporting skeletal growth in children.
- Calcium is particularly important during childhood due to the rapid rates of skeletal growth.
- Calcium is also involved in numerous metabolic processes, such as muscular contraction, enzyme-mediated processes, hormone and neurotransmitter release, and blood clotting.
Prevalence of Deficiency:
- The prevalence of calcium deficiency is not known due to insufficient data. However, the World Health Organization estimates that low intakes are common.
- Because there are no practical and reliable biochemical indicators of calcium status for population studies, dietary intake is currently the best method for estimating the prevalence of calcium deficiency.
- There is large variation in calcium intakes between countries, with the lowest intakes in developing countries. The highest intakes are in North America and Europe and the lowest in Asia.
Risk Factors for Deficiency:
- Low intakes of dairy products
- Infants and children under the age of 2 years are at particular risk for calcium deficiency due to the calcium required to support the rapid rates of skeletal growth.
- Pre-term infants may also be at particular risk for deficiency. Calcium accumulation occurs during the last trimester, and infants born early may not have laid down adequate calcium, resulting in inadequate calcium content at birth, increasing the risk for deficiency during infancy.
- There are no reliable biochemical indicators of calcium status. Serum calcium homeostasis is closely regulated and therefore does not reflect inadequate calcium status.
- Comparing dietary intake to the recommended nutrient intakes may be the best indicator of calcium status. However, there is variability in the recommended intake levels. For instance, the recommended calcium intake for infants is lower in Canada and the U.S. compared to the World Health Organization recommendations.
- Other methods, such as bone mineral density, bone mineral content, or measuring markers of bone resorption in urine or plasma, are expensive and are affected by other factors including vitamin D status, levels of physical activity, and hormone levels.
Dietary Sources and Bioavailability:
- Best dietary sources:
- Dairy products are the best source of dietary calcium. It is difficult to reach the recommended intake levels if dairy intake is low. In industrialized countries, dairy products provide 50-80% of dietary calcium.
- Plant foods supply a small amount of calcium. For instance in industrialized countries, plant foods supply about 25% of dietary calcium.
- Enhancers of absorption:
- Phosphate ion increases absorption and likely contributes to the increased absorption of calcium in human milk compared to cow’s milk.
- Vitamin D promotes calcium absorption.
- Inhibitors of absorption:
- Oxalates are the greatest inhibitors of calcium absorption. However, most diets do not contain large amounts of oxalates. Oxalates are found in plant foods, and high levels are present in spinach, sweet potatoes and beans.
- Phytates also inhibit calcium absorption. Phytates are found in legume and wholegrain cereals and are often consumed in large amounts.
- Sodium and animal protein decrease calcium status by increasing urinary excretion of calcium. However, this likely does not have a large effect on the calcium status in children whose dietary requirements are largely determined by the skeletal and growth requirements for calcium (rather than urinary excretion).
Recommended Nutrient Intakes (mg/day): The following are the Recommended Nutrient Intakes (RNI) as defined by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization.
- Toxic effects of excess calcium have only been observed when calcium is in the carbonate form and given in very high doses.
- The tolerable upper limit (UL) for calcium in children ages 1-3 years is 2500 mg/day.
- A variety of foods have been fortified with calcium, including wheat flour, juices, soy beverages, and other beverages.
- High calcium intakes through supplementation and fortification can interfere with iron absorption and need to be considered during any intervention.
Health Consequences of Deficiency and Benefits of Intervention:
- Health Consequences of Deficiency:
- Decreased bone mineralization: When calcium intake is inadequate, homeostasis of calcium concentrations in tissue fluids throughout the body are maintained at the expense of the skeleton. This results in bone demineralization which increases the risk for osteoporosis in adults and decreases skeletal growth in children.
- Calcium deficiency in children inhibits skeletal growth.
- There is also an increased risk for rickets in children.
- Bone mineral density increases until around age 30 years of age. Inadequate calcium intake during childhood and adolescents reduces peak bone density, increasing the risk for osteoporosis during adulthood.
- Health Outcomes Associated with Interventions in Children:
- Children in Gambia who were supplemented with 1000 mg of calcium per day, had improved bone mineralization.
Calcium. Vitamin and mineral requirements in human nutrition. Report of a joint FAO/WHO expert consultation on human vitamin and mineral requirements, Bangkok, Thailand, 21–30 September 1998. 2nd ed. Geneva: World Health Organization, 2004: 59-93.