Harsh socio-economic conditions affect the genetic health of children

Environmental health practitioners, particularly those who studied and qualified in the last twenty years, will be very familiar with Margaret Whitehead and Göran Dahlgren’s model of the social determinants of health, shown below in the well-known model from their 1991 publication.

Social determinants of health - Dahlgren and Whitehead 1991

Environmental health as a profession works at the interfaces between, generally, people’s living and working conditions and their health and wellbeing. But these are only one set of environmental factors that affect health in terms of morbidity and mortality, and there are other governmental and social actors that can work together to intervene and change the outcomes for real people in the real world. That’s why the new public health arrangements in England are game-changing for the profession and for the health of the public generally, and that’s why finding an evidence-base to target suitable and effective interventions that will really make a difference for people is so important.

A recent paper by Daniel Notterman and colleagues from Penn State University, and published in the Proceedings of the National Academy of Sciences of the United States of America, studied the genetic effects of harsh socio-economic environments on a group of children over a nine-year period. What they found was very striking – there was a statistically-significant shortening of the telomeres on the chromosomes of children who experienced a harsher socio-economic environment than those children who grew up in a more advantaged environment. And these effects were visible by the age of nine.

The story was picked up by several news outlets and New Scientist carried an article on it this week, which caught my attention and drew me to read the original paper.  I wanted to find out what was actually meant by “harsh environment” in the context of the research.

The authors chose a study group of African American children, and boys specifically, for this study. Choosing a single-sex group from a single racial cohort, as in this case, reduces some of the potentially-confounding factors for the study. The authors refer to research which indicates that boys may be more sensitive to negative family factors that girls.

In the context of this study, “harsh environment” means poorer, harsher parenting styles as against more nurturing styles, more changes in family structure particularly parental transitions, a younger mother at birth and poorer maternal educational achievement. A study group of 40 boys was chosen distributed between the harsh environment and more advantaged environments, where there was more stability in the family, a more nurturing parenting style, an older mother at birth and a mother with more educational achievement.

Telomeres are the repeating strings of TTAGGG bases at the ends of the chromosomes which are thought to protect functional genes  from damage during mitosis. Telomere length is a measure of the number of these repeats. Telomere length decreases over lifespan and are thought to be associated with aging and mortality. Therefore, the identification of factors which affect the telomere length in children and at such an early age is important in public health terms.

This study found as follows:

Model 1 (M1) of Table 2 shows that living in a disadvantaged environment was associated with a 19%shorter TL (P = 0.02). The next set of models (M2–M5) show the associations between boys’ TL and each of the environmental measures separately. Model 2 (M2) shows that a
doubling of the family income/needs ratio was associated with a 5% increase in the boys’ TL (P = 0.03). To provide more context for this estimate, in the larger Fragile Families sample the mean income/needs ratio is 0.7 for children at the 25th percentile and 2.7 for children at the 75th percentile, which is equivalent to an 8% difference in TL under this model. As a robustness test for economic conditions, we also examined the association between a boy’s TL and his mother’s education (see M5 in Table 2). Compared with children of mothers with less
than a high school education, having a mother with a high school degree is associated with a 32% increase in a child’s TL (P = 0.006), and having a mother with at least some postsecondary education is associated with a 35% increase in TL (P = 0.005). In sum, family economic status was a significant predictor of a boy’s TL measured in middle childhood. Model 3 shows that a low score on the parenting quality index was associated with a 3% decrease in a boy’s TL. Finally, model 4 shows that being exposed to multiple changes in family structure was associated with a 40% decline in a boy’s TL (P = 0.010).

As Dahlgren and Whitehead also write (Levelling up (part 1): a discussion paper on concepts and principles for tackling social inequities in health, WHO 2007),

… a stepwise, or linear, decrease in health – and not just an extreme group in poor health and the rest in reasonably good health – is seen with decreasing social position and is referred to as the social gradient (Marmot,2004). For example, the health of the populations of Florence, Leghorn and Turin has been followed over a number of years, and the findings clearly show that mortality increases linearly with increasing degree of social disadvantage. This is so both when social disadvantage is measured by the characteristics of individuals, such as education, employment or social class, and when it is measured by deprivation of the area in which people live …

This is a small study, and has some methodological problems, but it strongly suggests that public health workers need to look as closely at interventions in the family circumstances of children as at their physical environments if those children are to achieve their potential for long lives. Making them long, healthy lives is another challenge.

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