Life-Course Epidemiology

Ben-Shlomo and Kuh distinguish three. The critical- or sensitive-period model holds that an exposure has a lasting effect only when it occurs in a particular developmental window, the basis of biological programming. The accumulation-of-risk model holds that effects build with the total dose or duration of adverse exposure across life, regardless of exact timing. The chains-of-risk model holds that exposures are linked in a sequence, with early adversity raising the chance of later adversity that bears on disease. Real processes can combine these, and much life-course analysis is about deciding which model best fits a given outcome.

Conventional risk-factor epidemiology tends to relate exposures measured near the time of disease to the outcome, implicitly ignoring earlier life. Life-course epidemiology makes the timing and sequence of exposures central, asking when an exposure acts and how its effects compound over decades. This requires longitudinal data spanning multiple life stages and a shift from a single snapshot of risk to explicit models of developmental and social trajectories. It also integrates biological and social explanations, treating chronic disease as the product of an entire life history rather than of proximal adult behavior alone.

Because exposures at different life stages are usually correlated, a disadvantaged person tends to be disadvantaged throughout, so an early-life exposure and the lifetime cumulative dose carry overlapping information. An association with early-life conditions can therefore reflect a genuine sensitive period or merely the early portion of an accumulating burden. Disentangling them requires repeated measures, careful modeling that conditions early exposure on later exposure and total dose, and large samples; even then the models can be nearly indistinguishable statistically, which is why life-course epidemiology emphasizes triangulation with biological and social theory.