by Karen Switkowski, MS, MPH

Height is about more than physical appearance or the ability to reach items on the upper shelves of the grocery store. Economics research indicates that taller people make more money, even after controlling for factors such as age, gender, weight, education, and experience. In public health research, we often use height and growth rate as a study outcome when looking at the effects of various exposures, particularly nutritional factors. Height is an easily measured variable that can be used as a general marker of nutritional status and also predict health and developmental outcomes. What are some of the research questions that height is used to study?
A few weeks ago, Emily Oken wrote an interesting post about the link between stunting (i.e., impaired linear growth), early nutrition and brain development, and how stunting may impact future cognition and school performance in developing countries. Similarly, a recent analysis of data from five birth cohort studies from low- and middle-income countries indicated that more rapid linear growth in early life (before age 2) was associated with higher educational attainment.

Linear growth is also interesting as a research outcome in another context – one that is more relevant to studying populations that are not at risk of malnutrition. Height has been consistently associated with cancer risk in epidemiologic studiestaller people have a higher risk of cancer. This is probably due to the fact that height reflects a variety of other factors associated with cancer risk, such as energy intake, hormone levels, and genetics. Additionally, linear growth rate, or how fast someone grows in a given period of time, is associated with obesity and timing of onset of puberty, both of which have implications for future chronic disease risk.

While height and growth certainly have a strong genetic component, nutrition also plays an important role. In extreme circumstances, children who lack basic nutrition before and shortly after birth are at risk for impaired growth and its effects on future health and development. Even when babies are adequately nourished, their diet plays an important role in growth. For example, babies who are breastfed tend to grow slower (gain less weight, length, and adiposity) during their first year of life than formula-fed infants. Later on, they grow faster than children who were formula-fed as infants. This seems to be related to the protein content of the infant diet – breast milk contains a lower protein:fat ratio than does formula – and at least in part to the effects of protein on a growth-regulating hormone called insulin-like growth factor I (IGF-I).

Height is certainly an imperfect research measure. It may only be a marker of certain exposures that are truly responsible for the disease risk. However, the usefulness of height as a measure is its simplicity.  It is much easier to ask someone to stand on a height board than it is to take a blood sample and measure their hormone levels or gene patterns, or to assess the adequacy of their diet. For this reason, height and linear growth will probably continue to serve as key outcomes and exposures in a variety of public health research studies. 



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