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Smoking may kill off the Y chromosome in men’s blood cells, researchers said Thursday — a finding that may explain why men are more likely to die from smoking-related illnesses than women.

The team of Finnish researchers had already shown that men who are missing the Y chromosome from their red blood cells have a higher risk of cancer. They’re not sure why. For the latest study, published in Science, they looked at blood samples from about 6,000 men taking part in other health studies and looked at their blood samples and lifestyle factors including age, blood pressure, diabetes and drinking.

The more the men smoked, the more likely they were to be missing the Y chromosome in blood cells. But men who had quit smoking seemed to get the Y chromosome back, they found.

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“This discovery could be very persuasive for motivating smokers to quit,” Lars Forsberg, a researcher at Sweden'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.

IN-DEPTH

— Maggie Fox