Male smokers run higher health risks than women, say researchers whose genetic study could explain why men die from various cancers at a disproportionate rate when compared to women.

Male smokers are three times more likely than non-smoking men to lose Y chromosomes as they age, say scientists at Uppsala University in Sweden.

Its long been known that as men age the Y chromosome, important for sperm production and sex determination, can begin to disappear from cells in the body, a phenomenon once considered a normal process of aging.

However, some recent studies have suggested the process might not be benign, linking Y chromosome loss to a shorter life span and an increase of cancer.

The new study, published in Science, found older men who are smokers typically lose more Y chromosomes from their blood cells than non-smokers do.

That may explain why cancer risks among male smokers tend to be higher than in female smokers, says study leader Lars Forsberg of the university's Department of Immunology, Genetics and Pathology.

Data gathered by epidemiologists has shown male smokers face a greater risk of developing non-lung forms of cancer than do women who smoke.

Forsberg acknowledges that not all smokers show chromosome loss while some non-smokers do, and likewise many smokers do not develop cancer while many non-smokers do.

"But overall," he says, "smoking is associated with loss of Y, and loss of Y is associated with cancer."

The Y chromosome contains a large number of genes, and while the function of all those genes is not fully understood yet, some of them may help suppress tumors, Forsberg and his research colleagues suggest.

It may be that the "surveillance" for cancer carried out by the body's immune system is disrupted in those cells that have lost the Y chromosome, they suggest.

"The cells that lose the Y chromosome ... They don't die," says Forsberg. "But we think that they would have a disrupted biological function."

In analyzing data on more than 6,000 men, the researchers found that the amount of Y chromosome loss in smokers was apparently dose-dependent; in other words, the more a man smoked, the more Y chromosome loss he experienced.

The researchers also noted that in some men who successfully quit smoking there was an increase in levels of Y chromosomes as cells that had lost the chromosome disappeared from circulation.

"This discovery could be very persuasive for motivating smokers to quit," says Forsberg.