Recently, there has been a growing awareness in public health research of the long-term impact on health of various events and exposures earlier in life. Last year this journal introduced a section with several papers applying such a ‘life course perspective’, which illustrated the contributions that this perspective is already making to the field of social epidemiology.1,2
The first proponents of the ‘life course perspective’ concentrated on events and exposures in fetal life,3 but later studies showed that circumstances throughout childhood and adult age influence health in old age.4 A number of chronic diseases such as coronary heart disease, stroke, and some cancers seem to be influenced by factors acting across the entire life course. For researchers into the health effects of smoking it is of course not really new to realize that long-term effects are important. The concept of pack-year to express the lifetime exposure of smokers has been around since at least the 1970s. But there is increasing evidence that a number of other factors, operating at special critical periods earlier in life, may also influence health at later periods of the life course. For instance, infection with Helicobacter pylori during childhood seems to be the predominant cause of gastric cancer, and growth before and during puberty may be important for breast cancer development.4
It is a challenge for future public health research to disentangle the health effects of the complex interplay of social, behavioural, biological, and genetic factors across the entire life course. Most of what is known about risk factors for chronic diseases today, however, is restricted to studies that measured exposures operating in adult life. Fortunately, it has been possible to reconstruct a number of longitudinal studies initiated decades ago with prospectively collected data on growth and development in childhood for investigating early life influences on later health. The potential of these studies has been outlined in a number of cohort profiles published in the International Journal of Epidemiology during the past years. Further, several investigators in Europe have established new large birth cohorts with the capacity to study health across the life course and across generations in the future.
The aim of this growing body of data is to analyse the relationship between social, behavioural, biological, and genetic factors as they develop throughout an individual's life, and to assess their association with later disease. This aim leads to a natural ordering among the variables of interest which is determined by their time sequence, but which standard analytical methods ignore. Although innovative methods are beginning to be applied to capture dynamic trajectories,5 life course epidemiology is still restricted by limited expertise on how to analyse the data it originates.
Information gathered from this research is important for the prevention of chronic diseases, which according to some studies seem to have their origins even before conception. The current evidence suggests that the living conditions for young families should allow mothers to start pregnancy in a health-promoting environment, including adequate housing and a healthy lifestyle. Lifestyles become set relatively early in life; parents, teachers, health policies, and services provide key guidance leading to the development of a healthy or unhealthy environment. Prevention programmes should take advantage of these new insights, and development of a ‘life course perspective’ to prevention holds promise for great health gains in the future.