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 Some of these molecular changes revert to their original state when
a smoker quits, but others persist in the long term, the researchers
found.
Experts have known for some time that smoking causes changes of the
DNA molecule, but they are now learning more about how widespread
the changes are, and what they may mean, said senior author Dr.
Stephanie J. London, chief of the Epidemiology Branch at the
National Institute of Environmental Health Sciences in Research
Triangle Park, North Carolina.
“We don’t really know whether it means ‘damage’ to the DNA,” London
told Reuters Health. “That requires more study, using data outside
what we have here. What we’re saying is that it’s a change to your
DNA that can have a downstream effect on what genes are expressed at
what levels.”
The researchers combined data from 16 sets of participants in a
previous study of aging, totaling more than 15,000 people who had
provided blood samples that were analyzed for a type of DNA change
known as methylation.
The DNA molecule contains instructions for growth and development in
the form of genes, and so-called methyl groups along the molecule's
surface - collections of hydrogen and carbon atoms - can determine
which genes get activated.
The study team compared 2,433 current smokers - those who said they
smoked at least once a day sometime over the last year - to 6,518
former smokers who had stopped at least one year before the blood
draw and 6,596 never smokers.
Current smokers had 2,623 different methylated locations on their
genes compared to never smokers.
That corresponds to 7,000 potentially affected genes, many of which
are implicated in various cancers, high blood pressure and other
health outcomes of smoking, said lead study author Roby Joehanes of
Beth Israel Deaconess Medical Center and Harvard Medical School in
Boston. But future studies will need to complete the chain from DNA
changes to gene expression to disease outcome, he said.
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Only 185 of the methylated locations were still significantly
different between former smokers and never smokers, according to the
results reported in Circulation: Cardiovascular Genetics.
“Many people think that after five years your health is mostly back
to that of a nonsmoker, but that may not be the case,” Joehanes told
Reuters Health.
“Stop smoking now because many, many, many of the effects of smoking
will go away,” London said.
Since so many genes were involved, the researchers didn’t look at
individual changes and their possible health effects, she noted.
In future studies of other environmental influences on health, using
methylated DNA as a marker of former smoking may help rule out
tobacco as a confounding cause, she said. There is already an
effective test to detect recent smoking, but not one for smoking
that happened decades ago.
SOURCE: http://bit.ly/2cKnCJp Circulation: Cardiovascular Genetics,
online September 20, 2016.
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