by Karen Switkowski, MS, MPH
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 studies – taller 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.