8 CHAPTER 1 Importance of the first thousand days of life The period from conception to a child’s second birthday (i.e. the first thousand days of life) is crucial to children’s further physical, mental and social development (1-3). During these first thousand days, the foundations for optimal later health and wellbeing are established (3, 4). The body grows, the immune system develops and all vital organs are formed. The pace of development far exceeds that of any other phase in life. Moreover, it is the period in which our developmental plasticity, the ability to adapt to environmental factors and exposures, is highest (5, 6). Although our experiences across the lifespan can still influence our development to some extent, the first thousand days form the basis for who we are and have lifelong effects (7, 8). The well-studied Developmental Origins of Health and Disease concept (originally the ‘Barker hypothesis’) explains how early life experiences and exposures - both positive and negative - can influence later health and wellbeing (9, 10). There is an abundance of studies that show that many (chronic) health conditions such as diabetes, asthma, obesity, cardiovascular diseases, cancer and depression can trace their origins to early life (e.g. 11-18). This was demonstrated for instance by the findings of the Dutch Famine Birth Cohort study in which also timing of exposure appeared important (12, 19, 20). One of the described mechanisms of how early life exposures influence later health and wellbeing is through epigenetic programming. Epigenetic programming states that during critical times of development several factors can ‘program’ the bodily structures and functions to anticipate the environment it will face in the future (9, 10). Negative factors such as smoking during pregnancy, stress, pollutants and malnutrition can thereby lead to more susceptibility to diseases (21). For example, if a foetus is exposed to poor nutrition, it may adapt its metabolic system by storing more fat, which would be beneficial in case of food scarcity in adulthood, but can lead to obesity and other chronic diseases in an environment with abundant food (9, 10). These epigenetic changes can also be passed down from parents or grandparents to their offspring (8, 10). A better physical, mental, and social development during early life can lead to various positive outcomes in the future for both the individual as well as society, and thus should be at the centre of investments (22, 23). Some of those positive outcomes include improved learning and behaviour, enhanced educational opportunities, better job prospects, more productivity and greater participation in the workforce or society later in life (8). The Nobel prize-winning economist James Heckman showed that the best return on investment that society can achieve is by focusing its efforts on these first few years (24, 25). Investing early means that the benefits can be enjoyed for longer, and have a compounding effect. These benefits result from both higher revenues as well as savings in costs related to social welfare, poverty, crime and negative health outcomes. Moreover, early interventions are generally less costly compared to later remedial programs (24). Hence, early life investments are the most efficient and effective public investments.
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