Telomeres, which prevent chromosomes from unravelling over time.

Telomeres, which prevent chromosomes from unravelling over time. Photo: Supplied

Children who grow up in poverty or an unstable family show early signs of genetic ageing that may make them more vulnerable to certain diseases, a study has found.

Telomeres, the protective caps that prevent the ends of chromosomes from unravelling over time, were shorter in children who had a severely disadvantaged upbringing compared with children from privileged backgrounds.

The research highlights the effect a stressful environment can have on health from a young age.

While it is well known that chronic stress has negative health effects, the exact mechanism remains elusive, although shortened telomeres are thought to be a ''biomarker'' of the effect of stress on the body.

The ends of telomeres shrink each time a cell divides, a sacrifice that protects the genetic information at the ends of chromosomes. But when telomeres get too short, cells can no longer divide, and die. Many age-related diseases including cancer have been linked to shortened telomeres.

US researchers studied 40 African American boys and found, by the time they were nine, the telomeres of the children who grew up in a harsh home environment were almost 20 per cent shorter than those from advantaged backgrounds.

Boys whose mothers had more than one partner by the time they were nine had telomeres 40 per cent shorter than boys who had grown up in a more stable family.

The level of education of mothers was also associated with longer telomeres in offspring.

''We document significant associations between low income, low maternal education, unstable family structure, harsh parenting and telomere length,'' said study leader Daniel Notterman, of Pennsylvania State University.

The group, who published their results in journal Proceedings of the National Academy of Sciences, also found that specific gene sequences could increase how sensitive a child was to their environment.

The effect of these genes, which code for the brain the neurotransmitters serotonin and dopamine,

could amplify the stress of harsh environments for some children and magnify the advantage of privileged environments for others.

''Our findings suggest that an individual's genetic architecture moderates the magnitude of the response to external stimuli, but it is the environment that determines the direction,'' University of Michigan researcher Colter Mitchell said.

Previous research has shown children in Romanian orphanages had shorter telomeres than children who grew up in foster care.

The researchers studied African American boys because previous studies had been conducted almost exclusively on white children and other research had found boys were more sensitive to a bad home situation than girls, they said.

A 2012 report by the Australian Institute of Health and Welfare said many aspects of health, such as diet and smoking status, were related to wealth. In 2010, one quarter of people living in the lowest socioeconomic areas smoked tobacco, twice the rate of people living in wealthy areas.

In NSW, males born to well-off parents were expected to live about four years longer than babies born into poor, uneducated families.