Smoking can 'erase' the Y chromosome

Smoking can accelerate the loss of the Y chromosome in blood cells, a study claims. The findings may explain why smoking is a greater risk factor for cancer among men than it is for women. 

The researchers - who have previously demonstrated a link between loss of the Y chromosome and a risk of cancer - carried out DNA analysis of blood samples taken from 6,014 men in an attempt to identify clinical or lifestyle factors associated with this chromosome loss. They found that men who smoked had a lower Y chromosome count in their blood cells compared to those who did not.

'Out of a large number of factors that were studied, such as age, blood pressure, diabetes, alcohol intake and smoking, we found that loss of the Y chromosome in a fraction of the blood cells was more common in smokers than in non-smokers,' said Lars Forsberg, a researcher at Uppsala University, Sweden, and co-author of the study.

This loss is 'dose-dependent', meaning that men who smoked more had a greater proportion of their blood cells missing their Y chromosome. The scientists also observed that the proportion of blood cells without the Y chromosome was similar in men who quit smoking and in those who had never smoked, suggesting that the Y chromosome loss due to smoking may be reversible. This reversibility 'could be very persuasive for motivating smokers to quit', said Forsberg.

Tobacco smoking is a major risk factor for cancers, heart disease and other illnesses in both men and women. Epidemiological studies have shown that the incidence of cancer other than lung cancer is higher for male smokers than it is for women who smoke. Since the Y chromosome is found only in males, Professor Jan Dumanski, also of Uppsala University and who was involved in the study, suggested the findings may provide an explanation for why smoking is a greater risk factor for many cancers in men than women.

'In summary, we have shown that 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,' Professor Dumanski said. 'This finding may in part explain why men in general have a shorter life span than women, and why smoking is more dangerous for men.'

The exact mechanism through which Y chromosome loss precipitates non-lung cancer is not clear, but it is thought that Y chromosome loss in immune cells could make them unable to fight off invading cancer cells.

The study was published in the journal Science.