Contents - Previous - Next

5. Discussion

In this chapter we have discussed the three phases of linear growth in relation to the faltering process in length that is present in early life in most developing communities. The three phases of growth have been termed infancy, childhood and puberty, and they can be described mathematically in terms of the ICP growth model. Each of these three phases can be regarded in isolation, as being additive, and they are likely to represent three distinct endocrine phases.

Table 4. Weight and height of Hong Kong infants. Weight was taken at the monthly examinations in almost all infants, while length was measured at around 1, 7, 13 and 21 months of age in most of the infants. Mean and SD have been given for ages with 10 observations or more

Fig. 15. Mean weight SDS over the ages of Hong Kong infants based on the NCHS reference. Boys and girls are pooled.

Fig. 16. The incidence of stunting and low weight at different ages for the Hong Kong infants based on the NCHS reference. Both sexes are pooled and for each age and measure 180 to 220 observations were available.

Fig. 17. The distribution of length SDS at different ages based on the NCHS reference: the +0.5 SDS group, for instance, includes all infants with a length SDS of 0.0-0.99. Boys and girls are pooled.

The infancy phase is nutrition-dependent, the childhood phase GH-supported and the puberty portion driven by sex steroids, a hypothesis that is supported by current knowledge in endocrinology. One key point that is still very much debated is the time when GH starts to influence growth; some researchers believe that GH makes a major contribution to fetal growth, while others believe that it does not. In this chapter we have presented some empirical support for the view that GH may start to influence linear growth significantly at 6 to 12 months after birth, and that the onset of its action could very well correspond to the onset of the childhood phase of growth. Further research work is clearly needed to confirm this.

A delay in the onset of the childhood phase of growth seems to be the main determinant of the faltering in early growth. The reasons why the start of this phase is delayed in some children are still unclear. In normal Swedish infants, no relationship exists between the age at onset and season, feeding patterns, the age at which infants start walking, mid-parental height, or social group; only the growth rate prior to the age at onset is negatively related to the age at onset (Karlberg, 1989a; Karlberg et al., 1987a; Karlberg, Hägglund & Strömquist, 1991). In populations with a disturbed, or delayed onset, like the one in Lahore, we have not been successful in identifying any causal factors, when using information such as pattern of disease, feeding, or weight-for-length (unpublished observations). Further research is clearly needed in this area.

The incidence of faltering reflects socioeconomic standards, as shown in the Lahore study. These children lived in the same city and had the same ethnic background, but were brought up under very different conditions, from the privileged upper middle class group with good health care, housing standard and high parental education level to the very poor mud hut area in the periphery of the city with little or no health care provided and often illiterate parents. The upper middle class infants grew normally, without any clear signs of faltering, while the incidence of stunting reached 80% at 24 months of age in the poorer areas.

Clearly, environmental factors are a more likely cause of the stunting process than the ethnic or genetic background. Maternal illiteracy, poor hygiene, overcrowding, a high disease load and improper and/or contaminated food are all interacting in such environments. Whatever the causative factors are for the faltering process, they will remain if the general living conditions and educational level are not improved. Hong Kong has experienced a rapid socio-economic development during the last 40 years and is in many respects similar to Western European countries and North America. Despite this, some Hong Kong infants who are brought up under crowded conditions and belong to low or lower middle income families show growth faltering in early life, although to a much lesser degree than infants in poorer areas of developing countries. This suggests that it will take generations before the stunting problem has been eliminated, even in communities with fine financial resources and a well developed health care system.

Acknowledgements - This study was supported by grants from SAREC (the Swedish Agency for Research Collaboration with Developing Countries), the University of Hong Kong and the King Edward Medical College, Lahore, Pakistan.

Contents - Previous - Next