Physiologic programming of the fetus

In contrast to conventional theories, a series of provocative epidemiologic findings reported over the last decade suggest that environmental factors in early life are of substantial importance to disease risk in later years. To explain these findings, the idea of early life physiologic programming or imprinting has been advanced. Such programming has been documented in a variety of systems and reflects the action of a factor during a sensitive period or window of development to exert organizational effects that persist throughout life. Programming agents might include growth factors, hormones, and nutrients. These factors may produce adaptations that permanently alter adult metabolism and responses in a direction optimizing survival under continued conditions of malnutrition, stress, or other deprivation, but such responses might be detrimental when the later environment is unexpectedly less challenging.