MONDAY, July 6, 2020 (HealthDay News) -- Millions of Americans take medication to keep their blood pressure down. A new study suggests that two types of blood pressure drugs might do double-duty, keeping colon cancer away, too.
Angiotensin converting enzyme inhibitors (often called ACE inhibitors) and angiotensin II receptor blockers (ARBs) help lower blood pressure by relaxing and opening up narrowed blood vessels, allowing blood to flow freely.
Researchers analyzed the health records of almost 200,000 adult patients in Hong Kong from 2005 to 2013. Compared to nonusers of the drugs, those who took ACE inhibitors or ARBs had a 22% lower risk of developing colon cancer in the three years following a colonoscopy that declared them cancer-free, they found.
The researchers, from the University of Hong Kong, excluded all patients who had a prior history of colon cancer.
The benefit was especially true for patients 55 or older, and those with a history of colon polyps -- potentially cancerous growths.
In the three years following a clean colonoscopy, there is already low risk of developing colon cancer. Still, study author Dr. Wai Leung, a professor of medicine at the University of Hong Kong, said that cancer can develop during this period.
"We found that there's a very strong, protective effect, particularly within that short period of time after a negative colonoscopy," Leung explained.
But the protective effects only lasted for those first three years.
The results were published July 6 in the journal Hypertension. They showed that the drugs do not reduce the risk of all colon cancer, but are particularly beneficial in preventing colon cancer that arrives soon after a colonoscopy.
Colon cancer is the third most common cancer and the second leading cause of cancer death worldwide.
If commonly prescribed drugs could be repurposed to prevent colon cancer, it would have a significant public health impact, said Dr. Raymond Townsend, director of the hypertension program and a professor of medicine at the Hospital of the University of Pennsylvania.
Townsend said the results of this study are significant, especially since the researchers looked at such a large population.
"A 22% reduction is not trivial, so I think there's a story here," added Townsend, who had no role in the study.
The study also found that the longer you use the medications, the more likely you are to experience a benefit.
For every year that the patients took the drugs, the risk of developing colon cancer in the three years following a clear colonoscopy was lowered by 5%.
But Townsend emphasized that studies like this generate more questions than answers.
The population of people who take medications to lower their blood pressure are often older and have other risk factors for cancer.
As people age, their chances of developing high blood pressure go up dramatically -- as do their chances of developing cancer.
"You've got a population that is primed to develop the problem in the first place," Townsend said.
Since the study looked at people in the real world, there are risk factors and variables that naturally affect the results.
"Is it the person, or is it the medication?" Townsend wondered.
And prior research has shown the opposite effect -- that medications for high blood pressure could cause cancer, instead of preventing it.
"Since 1976 or so, this issue of cancer in patients on blood pressure medicines has been in the literature repeatedly," Townsend explained.
Based on how these blood pressure medications work, there is some reason to believe they could prevent cancer.
For cancers to grow, they have to develop new blood vessels, and blood pressure medications may block the formation of these new vessels.
"It's possible that these medications really cut off the blood supply of these tumors and prevent them from growing," said Dr. Andrew Chan, a colon cancer specialist and professor at Harvard Medical School. He was not involved in the study.
However, the study cannot show a direct cause-and-effect relationship. And Chan added, "one study is not enough to sway clinical practice, and you really need to verify that you have similar associations in other studies."
There's more about colon cancer at the American Cancer Society.
SOURCES: Wai K. Leung, M.D., clinical professor, medicine, University of Hong Kong; Andrew Chan, M.D., M.P.H., professor, medicine, Harvard Medical School, Boston; Raymond R. Townsend, M.D., director, Hypertension Program, Hospital of the University of Pennsylvania, and professor, medicine, Hospital of the University of Pennsylvania; Hypertension, July 6, 2020, online