Results of a new study published in the prestigious journal Science show that male smokers are at a greater risk of developing more cancers than female smokers, and the cause lies in their chromosomes.
Men carry an X and a Y chromosome in all their cells, as against women who have two X chromosomes. Male smokers are at a greater risk for developing more cancers because smoking causes their blood cells to lose the Y chromosomes.
The Y chromosome carries ‘tumor suppressor’ genes, therefore, a loss of the chromosome results in the loss of these essential genes making the cell prone to developing cancer. Previous studies have shown that the abnormal loss of the Y chromosomes from cells results in an increased risk to develop non-blood cancers. However, the cause for this loss of Y chromosomes from cells was not understood.
To understand the reason behind this loss of Y chromosomes, researchers at Uppsala University in Sweden examined the effects of several factors such as age, exercise status, diabetes, cholesterol, education, alcohol etc., and found that age and smoking were the only factors associated with Y chromosome loss.
In an earlier study published in April this year, this team of researchers studied 1150 elderly mean and showed that the loss of the Y chromosome from one-fifth of their blood cells almost doubled their risk of early death, shortening their life expectancy by an average of 5.5 years. This loss of Y chromosomes also quadrupled their risk of developing certain types of cancer.
In this follow up study in 6000 men, this team of researchers studied the effects of smoking on Y chromosomes in blood cells and found that smokers were, on average, three times as likely as non-smokers to lose Y chromosomes from their blood cells.
They also found that smoking causes a dose-dependent loss of Y chromosomes from blood cells, i.e., greater the number of cigarettes smoked, more the number of blood cells that lost the Y chromosome.
However, the good news is that this effect is reversible, if smokers quit, and former smokers had the same numbers of Y chromosomes as those in non-smokers.
Another reason to kick the butt!
In summary, the results of this study explained two long standing conundrums: 1) why is smoking a greater risk factor for cancer in men compared to women, and, 2) why do men have a higher incidence and mortality from most non-sex-specific cancers relative to women.
- Smoking is associated with mosaic loss of chromosome Y. Science, December 4, 2014 http://www.sciencemag.org/content/early/2014/12/03/science.1262092.abstract
Nature Genetics, April 28, 2014. http://www.nature.com/ng/journal/v46/n6/full/ng.2966.html