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National Study of Health and Growth. By Rona RJ, Chinn S. (Pp 133, hardback; £49.50.) Oxford: Oxford University Press, 1999. ISBN 0 19262 919 0
The youth of today are not what they were: they are bigger. Rona and Chinn, in their long and meticulous study of the health and growth of some 87 000 children, have documented the continuing trend to increasing height for age in primary school children over a 20 year period. This is generally thought to be a good thing and indicative of ever improving health and nutrition. The trend has been rumoured to be at an end many times, but in fact continues. Similarly, poverty was thought to be at an end in the 1970s when this study had its beginnings, only to be reluctantly rediscovered after the Black report. The two clearly go hand in hand: when there is no more poverty and perfect health and nutrition have been achieved, there will be no further gain in height. The effect of poverty is illustrated in this study, as in many others, by the social class gradient in height. Yet the exact mechanism of the relationship is mysterious as most of the gradient disappears after adjustment for parental height. The authors argue that most of the variation must therefore be genetic, others argue that there has been overadjustment.
The other secular trend observed has been of increasing obesity: a worrying trend in light of the much larger epidemic in adult obesity. But then again all is not what it seems. Mean weight for height is referred to throughout as “obesity”. Yet, as this is the age when children pass through the thinnest phase of their growth, few if any will be actually obese and presumably a proportion were actually underweight. When does less undernutrition become too much overnutrition, and how do we tell? So a paradox: the secular trend to increasing height is good and is due to improved overall nutrition. The parallel trend to increasing weight for height is bad and is due to improved overall nutrition.
No dataset can provide all the answers. By collating their long work and summarising all their analyses in this well structured and admirably slim volume, the authors make it possible for the idle and speculative like myself to argue with their conclusions. The range of the work is vast: from heart disease risk factors and asthma prevalence, to the prevalence of enuresis and food intolerance. It may come as no surprise that the last has a strong inverse relation with level of education, but the adverse impact of food exclusion on height certainly surprised me. No doubt future generations will dip into this rich dataset and pick out many more plums to inform both research and practice. We can be grateful to Rona and Chinn for making it possible.