American Journal of Epidemiology Advance Access originally published online on November 6, 2006
American Journal of Epidemiology 2007 165(1):114; doi:10.1093/aje/kwk096
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LETTERS TO THE EDITOR |
THE FIRST AUTHOR REPLIES
Department of Public Health, Faculty of Medicine, University of Helsinki, FIN-00014 Helsinki, Finland
(e-mail: karri.silventoinen{at}helsinki.fi)
We thank Mr. Samaras for his comments (1). We are well aware of the studies included in his and his colleagues' previous review article (2) but do not see any discrepancy between them and our current results (3). Samaras makes a fundamental error by assuming that the factors affecting the association between height and coronary heart disease (CHD) between populations would be the same as the factors affecting this association within populations. We found no reason to refer to the findings of the review, since they pertained to a totally different topic than we addressed in our article.
Virtually all of the studies referred to by Samaras analyzed the associations between height and CHD between populations—most of them between countries but some of them between ethnic groups or geographic subpopulations in the same country. It is clear that populations following westernized diets high in fat and energy content are, on average, taller and suffer more metabolic abnormalities such as obesity and hypercholesterolemia, leading to higher CHD mortality. Our study and many previous studies analyzed this association within populations following westernized diets. The association between short stature and high CHD risk indicates that in these populations, environmental factors affecting stature also affect CHD risk. The specific factors are not yet known, but insufficient nutrition in childhood, lack of important micronutrients, childhood diseases, smoking in the home during childhood, and fetal conditions—all known to be associated with shorter stature (4)—are likely candidates.
This fundamental error becomes even clearer when Samaras argues that the shorter stature and lower CHD risk in females versus males in some way contrasts with our results. It is clear that shorter stature in females is due to biologic factors, most likely the effects of hormonal differences during and after puberty (5), which have nothing to do with the environmental factors we suggest to be behind the association between height and CHD risk within populations.
In our article (3), we tried to make it clear that we do not assume—as suggested by Samaras—that short stature is a risk factor for CHD in the sense that, for example, obesity is a risk factor for CHD. It is important to note that 80–90 percent of variation in height within European populations is due to genetic differences (6), which, according to our study, are not associated with CHD risk. Thus, at the individual level, short stature should not be regarded as a risk factor for CHD. At the population level, however, height is an indicator of childhood environmental factors that also affect CHD risk in adulthood, at least in populations following westernized diets. It is likely that there are populations in which this association is reversed—if, for example, part of the population follows a westernized diet and part follows a traditional diet. However, this question was beyond the scope of our paper, in which we analyzed this association within European populations.
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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References |
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 TOP References |
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- Samaras TT. (2007) Re: "Association between height and coronary heart disease mortality: a prospective study of 35,000 twin pairs." (Letter). Am J Epidemiol 165:113–14.
[Free Full Text] - Samaras TT, Elrick H, Storms LH. (2004) Is short height really a risk factor for coronary heart disease and stroke mortality? A review. Med Sci Monit 10:RA63–76.[ISI][Medline]
- Silventoinen K, Zdravkovic S, Skytthe A, et al. (2006) Association between height and coronary heart disease mortality: a prospective study of 35,000 twin pairs. Am J Epidemiol 163:615–21.
[Abstract/Free Full Text] - Silventoinen K. (2003) Determinants of variation in adult body-height. J Biosoc Sci 35:263–85.[CrossRef][ISI][Medline]
- Silventoinen K, Kaprio J, Lahelma E, et al. (2001) Sex differences in genetics and environmental factors contributing to body-height. Twin Res 4:25–9.[CrossRef][Medline]
- Silventoinen K, Sammalisto S, Perola M, et al. (2003) Heritability of adult body height: a comparative study of twin cohorts in eight countries. Twin Res 6:399–408.[CrossRef][ISI][Medline]
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