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Cells exposed to
low doses of X-rays may delay or completely avoid repairing
damaged DNA, raising questions about the safety of routine
X-rays.
Surprisingly, cells
exposed to higher doses of X-rays repaired damage at a faster
rate. The study’s results were unexpected, but, according
to researchers, it is not known whether the reduced repair
capacity after low-dose X-rays is a good thing or a bad thing.
While unrepaired
breaks in DNA can result in cells becoming cancerous, faulty
repairs are also problematic. It may be that allowing a cell
to die and be replaced is safer than repairing the cell, researchers
said.
This is in-line
with the finding that cells exposed to higher doses repair
themselves faster; since more cells are damaged by the higher
doses, repair becomes a necessity.
In the study, researchers
exposed human lung cells to varying X-ray doses. Doses ranged
from levels typically received from routine medical and dental
X-rays (1.2 milligrays) to levels 10 times higher than are
received by patients undergoing CT scans (200 milligrays).
Cells that received
high doses repaired 95 percent of their damage within a day.
When cells were exposed to doses of 5.0 milligrays, the DNA
repaired fell to 80 percent. However, cells exposed to the
lowest doses either delayed repair for days or avoided repairs
entirely.
Researchers suggest
that chemical signals within or between cells could determine
whether repairs are essential or can be ignored. They note
that while further research is needed to explain these findings,
there doesn’t appear to be an immediate effect on X-ray
risk estimates and people should not stop having them.
Journal
Reference: Proceedings
of the National Academy of Sciences April 4, 2003 (doi/10.1073/pnas.0830918100)
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