Statin use and the level of cholesterol have already been linked to reduced colorectal cancer risk but until now, it has remained unclear which can be attributed to the apparent beneficial effects.

Now, a new study has shown that although a person's cholesterol levels may affect risk of colorectal cancer, long-term use of the cholesterol-lowering drug does not cut the odds of developing the disease, which is expected to kill more than 49,000 people in the U.S. in 2016.

For the new study published in the journal PLOS Medicine on April 26, University of Pennsylvania researchers compared the statin use and cholesterol levels of more than 22,000 people diagnosed with colorectal cancer and over 86,500 people without the disease.

They found that those who take statins have lower colorectal cancer risk, confirming findings from previous studies that showed a decreased risk of colorectal cancer in statin users compared to non-users.

The new study, however, found that the risk was not significantly different between the participants who continued using statins and those who stopped using them.

"Although the risk of colorectal cancer was lower in statin users versus nonusers, when we compared those who continued statin therapy versus those who discontinued the therapy, such that each group shared the same indication for statin therapy, there was no difference in risk," said study author Ronac Mamtani, from the University of Pennsylvania.

The observational analysis revealed that it is the cholesterol levels, and not statins, that influence the risk for the disease and that "indication bias" could be responsible for the association.

This bias happens when the indication, or the high cholesterol, being treated by the drug is linked to the outcome of interest, in this case, colorectal cancer.

"Although the risk of colorectal cancer was lower in statin users versus nonusers, no difference was observed among those who continued versus discontinued statin therapy, suggesting the potential for indication bias," the researchers wrote.

"We also demonstrate that increased serum total cholesterol is not a marker of long-term reduced risk of colorectal cancer; however, reduction in serum total cholesterol is a marker of short-term increased risk."

In related news, a 2015 study has shown that while statins may help lower cholesterol levels and risks for heart attack, taking the drug regularly may speed up the aging process that may cause decline in mental and physical health.

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