Secrets to a long life may lie with long-lived smokers, but researchers warn that's not a reason to start the habit - or continue it.

Jeanne Calment, the French doyenne believed to be oldest person in the world when she died at the extreme age of 122, was known for three things: her quick wit, her fondness for bicycling around the small city where she grew up - and the fact that she was a daily smoker.

Before her death in 1997, Calment was often asked the secret to her good health. She would respond with a laugh and describe how she would frequently consume two pounds (900 grams) of chocolate a week, drank generous amounts of port wine and became a smoker at age 21.

At a time when public health messages emphasise just how important it is to carefully balance diets and fitness regimes in order to live long lives, Calment is a reminder of that no matter what we do there may always be a part of our health that is beyond our control.

In an intriguing study published this week, researchers delved into the genetic makeup of long-lived smokers like Calment and found that their survival may be due to an innate resilience they were born with.

Morgan Levine, a post-doctoral fellow in human genetics and biostatistics at the University of California-Los Angeles, and Eileen Crimmins, a gerontology professor at the University of Southern California, discovered a set of genetic markers in these smokers that they believe may allow them to better withstand and mitigate environmental damage from stressors.

Smoking is known to be one of the worst things you can do to your body, with drastic consequences on life span and the progression of disease. On average, smokers' life expectancy is 10 years less than non-smokers. The long-lived smokers are the exception and the researchers said that their findings suggest they may be a "biologically distinct group" that is endowed with genetic variants that allow them to respond differently to exposure.

"There is evidence that these genes may facilitate lifespan extension by increasing cellular maintenance and repair," Levine said.

The study, which was published Wednesday in the Journals of Gerontology, Series A: Biological Sciences & Medical Sciences, involved participants of the longitudinal Health and Retirement Study in the United States. The researchers compared 90 participants who were smokers and lived to past age 80, with 730 people who were smokers and lived to less than 70 years of age.

They found that those in the age 80-plus group had similar physiological function as measured by inflammation, blood pressure and immune function as non-smokers in their age group. Smokers who died at a younger age had had worse physiological function than their same-age non-smoking counterparts at the time they were measured.

Levine said the work is important because "the more we know about why we age, the more equipped we will be to intervene".

"Ageing is an extremely complex process, and I think we are only beginning to uncover some of the mechanisms that regulate it. However, it also happens to be the biggest risk factor for most of the diseases that people suffer and die from," she said.

While the study has a number of limitations - its small sample size for one and the fact that things like disease status were self-reported - the researchers had enough information to develop a genetic risk score for smokers. They reported they were not only able to predict an individual's likelihood of surviving to a very old age - but a person's risk of cancer, which, not surprisingly, was significantly lower in those with the protective gene variants.

An important question smokers may have is whether they carry the genetic variants identified in the study.

While there are a number of companies that offer direct-to-consumer tests for genetic information, Levine said not all of them measure the same markers and "therefore, they may not have all the markers we presented in this paper".

Such a test may possible in the future, however. Levine is collaborating with other researchers at the University of Southern California's Davis School of Gerontology to develop tools that would allow individuals to calculate their health risks based on information from blood tests and genetics.

Levine emphasised, however, that the "proportion of people who have a 'genetic signature' that would help them cope with the biological stresses of smoking is extremely small, and therefore, nobody should use this paper as an excuse to continue smoking".

"Even among those who are genetically predisposed to longevity, smoking cessation is likely still one of the best things they can do for their health," she said.

With the focus on wellness in modern society, Levine said she's currently working on new research into people's "health spans" (as opposed to life spans), a term that refers to the length of a person's life that is disease and disability free.

"Our society has been conditioned to associate a very negative image with being old," she said. "However, we have seen that some people are able to live to be centenarians without ever suffering from disease and disability. This is the goal."