|Causes and Mechanisms of Linear Growth Retardation (International Dietary Energy Consultative Group - IDECG, 1993, 216 pages)|
|Adequacy of dietary mineral supply for human bone growth and mineralisation|
A. Prentice and C.J. Bates
Correspondence to: A. Prentice, MRC Dunn Nutrition Unit, Downhams Lane, Milton Road, Cambridge CB4 1XJ, UK.
MRC Dunn Nutrition Unit, Cambridge, UK, and Keneba, The Gambia
The evidence on the relationship between dietary mineral supply and bone development in children has been extensively reviewed. Data from children and primates suggest that overt deficiencies of Ca, P and Zn are likely to produce rickets and growth retardation, while the effects of Mg deficiency on human bone are unknown. The manifestations of marginal deficiencies are little understood. The biological needs for Ca, P. Mg and Zn in childhood have been calculated based on mineral deposition rates, using published values for the mineral content of the human body, and on obligatory endogenous losses. As a rough guide, the estimated biological requirements for the Ca, P. Mg and Zn can be taken as 200, 100, 4 and 1 mg/d respectively. A comparison of measured daily intakes of children in developing countries with biological requirements was made. This revealed that P and Mg intakes were many times higher than estimated needs. Ca intakes at all ages were found to be close to the biological requirement for children in many Third World societies, before any allowance for possible poor absorption. Zn intakes approach estimated needs in breast-fed infants, particularly during weaning, but are 4-5 times higher in older children. Poor absorption from phytate-rich diets could affect Zn supply. Supplementation studies indicate that raising Zn intakes can increase height gains in certain vulnerable groups, such as infant and adolescent boys. In conclusion, the evidence suggests that inadequate dietary intakes of Ca and Zn may contribute to linear growth retardation in children of developing countries but more research is needed.
We were asked to review the evidence on whether "deficiency or malabsorption of calcium, phosphorus, magnesium or zinc (Ca, P. Mg, Zn) affect linear growth and deposition of bone mineral in the human, given that the diets of Third World children tend to be low in these elements, even when breast-fed, and that this may be an important contributory factor in their poor growth performance."
This statement raises many fundamental questions that need to be examined:
1. What are the biological requirements of Ca, P. Mg and Zn for normal growth in the human?
2. What are the likely manifestations of an inadequate supply of Ca, P. Mg and Zn in the growing child? Do children in developing countries show signs that could be attributed to mineral deficiencies?
3. Are the mineral intakes of children in developing countries low in relation to the biological requirement or in comparison with well-nourished children in developed countries? Are diet composition and illness likely to affect mineral bioavailability? What is the contribution of breast-milk to mineral intakes in early childhood?
4. What evidence do we have that increasing the intakes of these minerals would improve growth or bone development in Third World children?
In the following paper, each of these questions will be discussed in detail and the evidence that is currently available will be reviewed.