Children from families with low income, whose mothers had not completed high school, and whose families scored highly on the study's 'harsh parenting index' had telomeres around 19 percent shorter than those from more nurturing environments.
'I'm not surprised we found such a relationship and I'm not surprised by the gene interaction. I'm surprised by the magnitude of the association', said Professor Daniel Notterman from Pennsylvania State University, who led the research.
Telomeres are strings of DNA that act as caps on chromosomes that prevent them from unravelling or joining to other chromosomes. They are linked to ageing because they become shorter each time a cell divides. As a person gets older and their cells have divided many times, telomere length is reduced.
The researchers studied the DNA of 40 nine-year-old African-American boys and discovered a strong correlation between social environment and telomere length. They also found that telomere length is mediated by a pair of genetic pathways that are involved with the mood-regulating neurotransmitters dopamine and serotonin, 5-HT (5-hydroxytryptamine).
Two genes have been suspected to cause sensitivity to environmental factors: TPH2, which has been implicated in depression, bipolar disorder and other mental health issues, and 5-HTT, a gene for a serotonin transporter. Some variants of these genes lead to greater environmental sensitivity, leading to significantly shorter telomeres in boys from disadvantaged families and longer ones in the children from more advantaged backgrounds.
The researchers believe that telomere length should be used as a biomarker for chronic stress exposure and may signal that intervention is needed to prevent long-term health effects. 'The demonstration that telomere length is shortened by age nine supports the idea of early intervention', said Professor Notterman.
The study was published in the journal Proceedings of the National Academy of Science.