Health inequalities: Is the foundation for these laid before the time of birth?
Dwyer T., Morley R., Blizzard L.
Introduction Barker’s original idea of the ‘foetal origins’ of cardiovascular disease (CVD) and chronic lung disease in adulthood relates to foetal under-nutrition in a malnourished mother. There is evidence suggesting that when the foetus receives an inadequate supply of nutrients, its growth is slowed and blood flow is redistributed preferentially towards the brain. It is hypothesised that these adaptions result in reduced weight at birth, and structural or metabolic adaptations that predispose the foetus to disease in adult life (Barker 1991). Lower socio-economic status (SES) is associated with lower birth weight (Pattenden et al. 1999), and it has been suggested that the harmful effects of low SES on adult health may be mediated via a pathway involving foetal under-nutrition and low birth weight (Barker and Martin 1992). The implication is that preventive efforts aimed at reducing diseases of adults need to embrace measures to alleviate social inequalities in women of reproductive age In this paper, we discuss the findings of our own research that suggest the link between social status and adult disease can be explained largely by differences in foetal development. Health effects of low birth weight There are now a very large number of studies that have shown that babies who are small at birth have a higher risk of adult cardiovascular disease (Leon et al. 1998) and diabetes (Hales 1997). The following data (table 16.1) from the Nurses Health Study in the United States (Rich-Edwards et al. 1997) demonstrate just how strong an effect this might be. Risk factors for these diseases such as higher blood pressure and impaired glucose tolerance are also found more commonly among children and adults who were small at birth. The association between low birth weight and SES Could this apparent effect of low birth weight explain the known associations of SES with CVD and diabetes, and possibly with other diseases? The available evidence does show that low birth weight is more common in lower SES families. For example, we have found that 30% of the occurrence of low birth weight (defined as less than 2500g) in a sample of British children can be attributed to the effects of social inequality. These subjects were 921 children recruited into two large infant nutrition studies (Lucas et al. 1999; Lucas and Morley personal communication) and randomised to bottle-feeding or to the breast-feeding ‘control’ arm.