|Causes and Mechanisms of Linear Growth Retardation (International Dietary Energy Consultative Group - IDECG, 1993, 216 pages)|
|Is complete catch-up possible for stunted malnourished children?|
Clearly, if an insult sufficient to retard growth is imposed after the major components of growth have occurred, then there will be no discernable effect. Equally, if the insult operates for only a short time, then there are unlikely to be any sequelae, unless it permanently changes genetic expression. The insult has to be imposed for a sufficiently long time for a discernable difference from the normal child (the standard) to be established. Just how chronic the insult has to be is often not appreciated.
Suppose that a completely normal child, of a certain age, reduces his growth rate so that he either ceases growth altogether (0%) or continues to grow at either 30%,50% or 70% of the rate at which he should have grown. The curves in Fig. 1a show the length of time, at each starting age, before the child falls 2 SD below the reference. As he gets older, the reduction of growth has to last longer and longer for him to be recognised as stunted. Thus, if a child stops growth completely at 12 months he reaches -2 SD after nearly 6 months (age 17.7 months); if he stops at 36 months, it takes 13 months (age 49 months) to reach the same point. However, an insult usually retards but does not stop growth. If growth continues at a reduced rate, then it will take longer for a child to fall below -2 SD. This is illustrated in the figure for various degrees of reduced, but continued, growth. Thus, if the 12 months old child reduces his growth rate to 30% of normal (reduced by 70%) he will take 10 months to become stunted (age 22 months), if the growth rate is only reduced to 70% of normal (reduced by 30%) he cannot be diagnosed as stunted until he is 52 months old.
Fig. 1. The time necessary for a child to fall from the median height-for-age to more than 2 SD below the median, if not gaining height at all (dotted line 0%) or gaining at 30% (short dash), 50% (long dash) or 70% (continuous) of the normal rate. The upper graph (a) shows the number of months it will take for a child to become stunted, in the future, if he commences to grow more slowly than normal. The lower graph (b) shows the number of months it has taken a stunted child, during his past life, to become stunted if growing normally and then at a reduced rate.
Fig. 1b is similar except that, instead of looking forwards in time to predict when a child will fulfil the criterion for stunting, it is looking backwards in time to show for how long an already stunted child, of a certain age, has been stunting if he has not been growing at all (0%) or has been growing at a reduced rate relative to the standard.
It is quite clear that an insult has to substantially reduce the growth rate for most of the child's life for him to become stunted. Successful reversal will require a complete and permanent removal of the retarding factors. This rarely happens.
The sheer chronicity of the process means that intercurrent infections, of themselves, are unlikely to cause stunting even if they are repeated. One should not expect a few episodes of acute diarrhoea to cause stunting (Briend et al., 1989; Moy et al., 1990), although, when this was first proposed it caused a flurry of dissenting correspondence in The Lancet (Schorling & Guerrant, 1990). Even when diarrhoea is statistically associated with stunting, only a small proportion (10%) of the retardation can be ascribed to this cause (Martorell et al., 1975). On the other hand chronic dysentery and persistent diarrhoea are, as expected, associated with stunting (Henry et al., 1987; Briend et al., 1989).
This chronicity is also important for catch-up potential. If a child is 12 months behind in his height growth, then he will have to grow at twice the rate of a normal child of his current height-age for at least 12 months to catch up; this is faster than twice the rate of a normal child of his chronological age, because the rate of normal height gain decreases with age. The older, and the further behind, the longer he will have to maintain a greatly accelerated rate of growth for full catch-up. A stage may be reached where there is simply insufficient time remaining to make a full recovery. It is also clear that increased rates of height gain, to be maintained over a prolonged period, will usually require a permanent change in the subject's environment; an input for a few months is only likely to lead to the start of catch-up.