The team looked at epigenetic changes, which are modifications to DNA that turn genes 'on' or 'off.'
With epigenetic changes, the underlying DNA sequence remains unchanged, but cells start to 'read' genes differently, almost like switching programmes on washing machine, or dimming a light. The changes alter how the body functions and can trigger disease.
Damaging environmental factors such as smoking, stress, pollution or obesity cause the alterations, and the culmination of epigenetic changes can be used like a clock to determine how fast a person is ageing.
Dr Eileen Crimmins, Professor of Gerontology, at the University of Southern California, said: "Some people who are 57 or older look like they're in their twenties, while some people look like they're over 100, and there's a big range in between.
"We think that adverse social experiences can change your epigenetic profile in ways that may subsequently influence your health adversely.
"There were people who looked 36 years younger, while some look 48 years older.
"We're trying to understand ageing health changes and the biological pathways so that we can better understand what we're really interested in, which is social differentials and ageing.
"People believe that the underlying process of ageing is one that underlies all the different health outcomes link to age, such as cognitive decline, disease, disability, frailty and mortality."
Researchers took blood samples from participants and tested them against three 'epigenetic clocks' which have been devised by scientists in recent years, to measure DNA changes at different points of the genetic code.
Their goal was to find out which social factors were speeding up or slowing the ageing process and so they compared the clock results to participants' education, life traumas, mental health, race and sex to see if they could tease out which events were contributing to ageing.
"We have lots of evidence that these social factors are linked across the board to the major health outcomes associated with age, and we're attempting to try to understand the biology of how social factors affect ageing outcomes," added Prof Crimmins.
They found that being female slowed down the ageing clock by up to two years, while obesity speeded it up by up to 18 months. Suffering psychological distress also increased biological age by around four months, and poor childhood health was also found to accelerate ageing.
However the results threw up some unexplainable findings. The clocks appeared to show that low socioeconomic status in childhood and having a drinking problem delayed ageing.
"Across the board the clocks related being female to decelerated ageing which makes sense, given what we know about mortality," added Prof Crimmins.
"Childhood health problems and negative psychological problems both make you look epigenetically somewhat older.
"Drinking problems are actually in the wrong direction but we find that obesity increases epigenetic age by about one and a half years. So some of it makes sense, and some of it sort of doesn't."
The research was presented at the AAAS meeting in Seattle and full findings are due to be published in March.
