Risk of getting lung cancer higher than that for fatter smokers, non-smokers: Study

SKINNY smokers, beware. Thinner smokers have a higher risk of lung cancer than their fatter counter parts, researchers found in a survey here.

And compared with slender non-smokers, slim people who light up are 11 times more likely to contract the disease.

But the study's lead author, National University of Singapore epidemiologist Koh Woon Puay, emphasised that those who smoke are still more likely to contract lung cancer overall than those who do not. Lung cancer is the second most common cancer in men here, and the third most common in women.

The research, published in the British Journal of Cancer in January, was part of the Singapore Chinese Health Study, which surveyed 63,257 middle-aged and elderly Chinese Singaporeans from 1993 onwards. It examined the relationship between smokers' body mass index (BMI) - a measure of obesity - and their chances of lung cancer. Normal ly, a higher BMI is a red flag for many diseases, such as diabetes, heart disease and colorectal cancer, Dr Koh explained.

Rut when it comes to puffing on cigarettes, the reverse is true. Pack-a-dav smokers with a BMI of at least 28 were six times as likely to get lung cancer as equally heavy people who had never lit up.

But thinner pack-a-day smokers, who had a BMI of less than 20, were 11 times as likely to get the disease as non-smokers of a similar weight and BMI.

That was true even when those with other respiratory diseases like tuberculosis and asthma, who were likely to be thinner than average, were removed to avoid skewing the data.

Among non-smokers, BMI had no effect on lung cancer risk.

Thee findings were especially worrying, said Dr Koh, as other research has shown that more young women are now lighting up to keep then weight down, due to the belief that nicotine suppresses the appetite and increases the metabolic rate. The proportion of young wom«n aged 18 to 29 who smoked every day rose to 6.6 per cent in 2004, up from 5.2 per cent in 1998.

"Young women may smoke ro stay slim, but that very factor - staying lean - may be the thing that will kill you with lung cancer," Dr Koh said.

She said researchers are not yet clear why thinness is a risk factor for lung cancer in smokers. It could be that leanness itself contributes somehow to the cell damage that leads to cancer.

But this does not mean skinny smokers should pile on the pounds to lower their cancer risk, as that makes them vulnerable to other diseases.

Oncologist Chin Tan Min, of the National University Cancer Institute Singapore, said; ''This can potentially lead to important insights for predisposing factors in lung cancer development.'' She was not involved in the recent research.

Dr Koh said further studies may try to identify the risk factors that make some smokers more vulnerable to lung cancer than other smokers.

This will improve screening and early detection for lung cancer, she said.