Previous research has shown that a low socioeconomic status leaves people more likely to suffer from increased risk of heart disease, diabetes, cancer and infections. But now, scientists led by Professor Thomas McDade at Northwestern University have found that this may be because being poor affects genes at the DNA level.
What did you find in the study?
We’ve known for a long time that individuals who have a lower level of socioeconomic status suffer from worse health throughout their lives. They die earlier, they are at increased risk of cardiovascular diseases, metabolic diseases, infectious diseases – basically everything on the social gradient of health.
But it’s been a bit of a mystery how that happens. How is it that our bodies in a sense remember the experiences that we have had growing up? And how do those experiences – in this case experiences associated with socioeconomic status – affect cellular function and physiology with implications for health?
We found that lower levels of socioeconomic status were associated with DNA methylation on a large number of sites across a large number of genes – more than 1,500. To me, this was somewhat surprising. We are showing that socioeconomic status touches nearly 10 per cent of the genes in our bodies and has the potential to affect their structure and function.
We are finding that DNA methylation might provide this mechanism for memory, for translating the experiences with respect to socioeconomic environments into biology and then possibly downstream to health.
So what exactly is DNA methylation?
All of our cells contain DNA, which is a series of sequences of bases known as A, G, T and C. DNA methylation is a biochemical process where methyl groups are added to particular sites in the DNA sequence called ‘CPG sites’.
In the genome, there are areas where there are clusters of these CPG sites. The methyl groups get added to these sites and they affect the likelihood that a gene will be expressed. That’s what really matters. You can inherit a gene from your parents that might have some adverse consequences on your health, but if that gene is not expressed it doesn’t matter.
Where does this fit into the whole nature versus nurture argument?
We tend to think of genes as something that is fixed that defines our destiny. We inherit them from our parents, and therefore at conception our fate is sealed. That’s a relatively simplistic model of genetic determinism, which is surprisingly common.
But this idea is not up to date with contemporary genomics and how we know genes matter to health. The term ‘epigenetics’ literally means ‘on top of the genome’. It’s the broader class of modifications to the structure of genes that affect their function.
One of the fascinating opportunities in this line of research, especially when we talk about epigenetics, is to think about the genome as part of our biology that needs input from the environment to shape its development and function. It challenges us to think about genes a little bit differently, to think about the genome as a dynamic substance that literally changes its structure and function in relation to experience.
Experiences that you have as you grow up shape the biochemistry of your genes in altering their structure and function. So to me, the whole nature and nurture thing totally breaks down. Genes cannot function in a vacuum. Similarly, environments can’t have effects on our bodies and health independently of their impact on the genome without shaping patterns of gene expression. There is no nature versus nurture. It’s nature through nurture – nature and nurture working together in conversation through the course of development.
Did you manage to pinpoint any specific effects?
We can’t answer that with this study but that is where we are going next. We are following these participants so we will be able to see what patterns of methylation at one point in time during young adulthood predict health problems later in life.
We have a lot of data from multiple points in time where we can look at where individuals accessed healthcare, how much food they ate, what kind of food they ate, how frequently they were sick. That’s where we are going to go next.
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