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Male smokers are three times more likely than non-smoking men to lose their Y chromosomes, a new study has found.

The research may explain why men develop and die from many cancers at disproportionate rates compared to women.

A recent study found an association between Y chromosome loss and a shorter life span, as well as a higher risk of multiple cancers. 

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Since only men have Y chromosomes, the new finding offers a possible answer to why smoking is a greater risk factor for cancer among men than women.

In a study in the journal Science, researchers at Sweden's Uppsala University found that Y chromosomes, which are important for sex determination and sperm production, more often disappear from blood cells of smokers than those of men who have never smoked or of men who have kicked the habit. 

Since only men have Y chromosomes, the finding offers a possible answer to why smoking is a greater risk factor for cancer among men than women.

Women have two X chromosomes; males have an X and a Y. 

'There is a correlation between a common and avoidable risk factor, that is smoking, and the most common human mutation -- loss of the Y chromosome,' said Jan Dumanski, an Uppsala professor who worked on the study.

'This ... may in part explain why men in general have a shorter life span than women and why smoking is more dangerous for men.

'This discovery could be very persuasive for motivating smokers to quit.' 

Besides lung cancer, which is caused by smoking and is often fatal, tobacco smoking is known to be a major risk factor for a range of serious illnesses. 

It is the world's leading preventable cause of premature death from chronic conditions such as heart disease, strokes and high blood pressure.

Epidemiological data show male smokers have a higher risk of developing non-lung forms of cancer than women who smoke.

The team analysed data on more than 6,000 men, taking into account their ages, exercise habits, cholesterol levels, education status, alcohol intake and many other health and behavioural factors.

Besides lung cancer, which is caused by smoking and is often fatal, tobacco smoking is known to be a major risk factor for a range of serious illnesses.

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They discovered that in smokers, the loss of Y chromosomes appeared to be dose-dependent -- in other words, men who smoked more lost more -- and that some men who went on to quit smoking appeared to regain their Y chromosomes.

Lars Forsberg, who also worked on the study, said this suggested Y chromosome loss due to smoking might be reversible

'This discovery could be very persuasive for motivating smokers to quit,' he said.

The scientists are not sure how loss of Y chromosomes in blood cells is linked with the development of cancer, although one possibility is that immune cells in blood that have lost their Y chromosome have a reduced capacity to fight cancer cells.  

'This discovery could be very persuasive for motivating smokers to quit,' Lars Forsberg, a researcher at Finland's Uppsala University who led the study, said in a statement.

The Y chromosome is of course the stretch of DNA that makes a man. Women have two X chromosomes; males have an X and a Y. But the Y chromosome controls more than the production of male hormones. It may affect how the body fights cancer, the Finnish team said.

And other studies have shown that men are more likely to get non-lung cancers from smoking than women are — from bladder cancer to colon cancer.

It might be that smoking damages DNA in general and that the Y chromosome, which is one of the smallest chromosomes in the human genome and already mutation-prone, is just more vulnerable, the researchers say. More research is needed to get the answer.