Tall is beautiful and heart-healthy?

A large number of studies have assessed the association between stature and coronary heart disease risk in many populations. Within a population, people of short stature seem to have a higher risk of coronary heart disease than taller people. Thus far, these data have not been subjected to a formal meta-analysis. Therefore, the systematic review and meta-analysis on this topic carried out by Paajanen and co-workers is well justified 60 years after the first observation and the hundreds of other papers which have been published since then on this topic. The results are unequivocal: short stature is associated with increased risk of coronary heart disease. This meta-analysis provides solid proof for this, but, as the authors conclude ‘The possible pathophysiological, environmental, and genetic background of this peculiar association is not known’. This systematic review of 52 observational studies comprising .3 million individuals is very impressive, and the full meta-analysis comprised 22 studies. The overall finding shows that short stature is associated with an increased coronary heart disease risk (95% confidence interval 1.37–1.55) compared with the tallest individuals in almost all studies included. There are, however, several issues that need to be discussed. First, observational studies are often prone to various confoundingeffects.Confoundingoccurs when two factors are associated with each other or ‘travel together’ and the effect of one is confused with or distorted by the effect of the other. A confounder is a variable which is associated with the exposure, and independently of that exposure is a risk factor for the disease. Observational studies are needed for the assessment of effects of factors that cannot be subjected to randomized controlled trials. Stature is in principle modifiable, and it varies between populations and over time, but it cannot be a target of a controlled trial. Short stature is associated with lower socio-economic status that in turn is related toan increased coronary heart disease risk. Secondly, it is well known that in all populations women have a lower incidence of coronary heart disease compared with men, although women are shorter—thus the ‘within population association does not hold’. Since the association between stature and coronary heart disease risk is found within each sex, sex is clearly just an effect modifier. Thirdly, in a between-population comparison, coronary heart disease risk is not higher among those populations that have shorter stature. Fourth, it is also important to pay attention to secular trends in both stature and coronary heart disease. For instance, in Finnish men, a linear increase in height of 1.3 cm per decade has been reported during the 20th century, in keeping with the data from other industrialized countries. However, a continuous increase in coronary heart disease mortality took place until 1970, followed by a steep decrease during the last 40 years both in Finland and in many other western countries. These discrepant trends indicate that short stature is biologically not causing coronary heart disease. Is this risk difference really due to short stature or do taller people carry some protective effects that lower their risk compared with their shorter fellow citizens? Very large differences in coronary heart disease incidence were observed between eastern (higher) and western (lower) Finland, especially in the second half of the 20th century. As a part of the Seven Countries Study it was noted that men in eastern Finland were shorter. Nevertheless, in both areas, short stature was an independent risk factor for coronary heart disease after the adjustment for major coronary risk factors such as serum cholesterol, blood pressure, and smoking. Interestingly, in taller men (.172 cm) no difference in incidence of coronary heart disease was observed between the two regions (Table 1). Thus, something related to short stature must have been involved in the risk of coronary heart disease in men in eastern Finland, and this is not explained by the major coronary risk factors alone. Various environmental, mainly nutritional, factors influence human growth at all stages of development, starting from the prenatal period, and postnatal conditions also have many effects on growth. It is well known that prenatal factors have a strong influence on foetal growth, in particular trunk growth, whereas legs grow more postnatally than the trunk. Intrauterine nutritional problems are related to many health problems in adulthood,