Early days in life can not only affect people's physiology,immune system,metabolism and structural development,but also can alter body cell functions in long term,which in turn has an impact on human's health and diseases both in short and long term.Thus,early days,especially the first thousand days in lifeplay an important role in human health and is thought to be a key period for preventing certain diseases later in life,which is under heated investigation.However,the mechanisms for this impact are not clear.This review emphasizes the importance of the first thousand days in humanlife and elucidates its association with human health from multiple aspects.