THURSDAY, Dec. 4, 2014 (HealthDay News) -- Men who smoke may see more of their Y chromosomes disappear as they age, a new study suggests.
Scientists have long known that as men grow older, the Y chromosome can start to disappear from some of their body cells. And that was initially thought to be a normal part of aging.
But recent research has suggested that "loss of Y" might not be so benign. In a study reported earlier this year, researchers linked Y chromosome loss to a shorter life span and an increased risk of dying from cancer, specifically.
The new study, published online Dec. 4 in Science, adds to those results: It found that older men who smoke typically lose more Y chromosomes from their blood cells than non-smokers do.
The finding hints at one possible explanation for why male smokers tend to face higher cancer risks than female smokers, according to Lars Forsberg, a researcher at Uppsala University in Sweden who led the study.
There are smokers who don't show a loss in the chromosome, and non-smokers who do, Forsberg noted -- just as many smokers don't develop cancer, and many non-smokers do.
"But overall," he said, "smoking is associated with loss of Y, and loss of Y is associated with cancer."
Men have an X and a Y chromosome, while women have two X chromosomes. And experts used to think that the Y -- short and stumpy compared with the X -- did little more than determine male sex and ensure normal sperm production.
"The bottom two-thirds of the Y chromosome was seen as just repetitive DNA that doesn't code for anything," explained Dr. Martin Bialer, a medical geneticist at North Shore-LIJ Health System in Great Neck, N.Y.
"But now we're starting to think it may have more roles than just determining sex -- though that's a pretty important one," said Bialer, who was not involved in the study.
Recent research has shown that the Y chromosome actually contains a large number of genes. Their jobs are not fully understood yet, but a couple of those genes may help suppress tumors, according to Forsberg's team.
It's possible, Forsberg said, that the immune system's cancer "surveillance" is disrupted in cells that lack the Y chromosome.
But Bialer said that while that's plausible, it's also "a pretty big leap." For one, he noted, loss of the Y chromosome may just be a "marker" for other chromosome damage caused by smoking.
Plus, research into the functions of Y is really just beginning, Bialer pointed out. "What we can say from this," he said, "is that smoking seems to cause a loss of Y, but we're not really sure yet what the significance is."
For the study, the researchers analyzed blood samples from more than 6,000 older men taking part in three separate studies. Overall, about 15 percent of men aged 70 and older had a significant loss of the Y chromosome (affecting at least 10 percent of their blood cells), according to the study.
But current smokers were two to four times more likely to show loss of Y than non-smokers were, the investigators found.
The researchers also looked at some other potential risk factors for Y chromosome loss -- such as high blood pressure, excess weight, diabetes and lack of exercise. But only smoking and older age showed an effect.
And, the effect appeared to be more pronounced the more someone smoked, according to the study.
On the bright side, Forsberg pointed out, former smokers were similar to men who had never smoked. That might give male smokers some extra motivation to quit, he said.
And what about women? They lose X chromosomes in their cells as they age, Bialer said. But the possible health consequences are not known.
The U.S. National Library of Medicine has more on the Y chromosome.